diff --git a/src/Cargo.lock b/src/Cargo.lock
index c22187ee13e8e..7756801a46c45 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -1392,6 +1392,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "proc_macro"
 version = "0.0.0"
 dependencies = [
+ "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
@@ -1753,6 +1754,7 @@ dependencies = [
  "graphviz 0.0.0",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc 0.0.0",
+ "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
  "rustc_mir 0.0.0",
  "syntax 0.0.0",
@@ -1948,6 +1950,7 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_const_eval 0.0.0",
  "rustc_const_math 0.0.0",
+ "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
@@ -1973,6 +1976,7 @@ name = "rustc_privacy"
 version = "0.0.0"
 dependencies = [
  "rustc 0.0.0",
+ "rustc_data_structures 0.0.0",
  "rustc_typeck 0.0.0",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
@@ -2374,6 +2378,7 @@ version = "0.0.0"
 dependencies = [
  "fmt_macros 0.0.0",
  "proc_macro 0.0.0",
+ "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
diff --git a/src/libproc_macro/Cargo.toml b/src/libproc_macro/Cargo.toml
index cfd83e348a8e2..c1b2622520b11 100644
--- a/src/libproc_macro/Cargo.toml
+++ b/src/libproc_macro/Cargo.toml
@@ -11,3 +11,4 @@ crate-type = ["dylib"]
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc_errors = { path = "../librustc_errors" }
+rustc_data_structures = { path = "../librustc_data_structures" }
diff --git a/src/libproc_macro/lib.rs b/src/libproc_macro/lib.rs
index 41ccd88b4a887..66fabcb73d95b 100644
--- a/src/libproc_macro/lib.rs
+++ b/src/libproc_macro/lib.rs
@@ -43,6 +43,7 @@
 extern crate syntax;
 extern crate syntax_pos;
 extern crate rustc_errors;
+extern crate rustc_data_structures;
 
 mod diagnostic;
 
@@ -50,7 +51,7 @@ mod diagnostic;
 pub use diagnostic::{Diagnostic, Level};
 
 use std::{ascii, fmt, iter};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::str::FromStr;
 
 use syntax::ast;
@@ -277,7 +278,7 @@ pub struct LineColumn {
 #[unstable(feature = "proc_macro", issue = "38356")]
 #[derive(Clone)]
 pub struct SourceFile {
-    filemap: Rc<FileMap>,
+    filemap: Lrc<FileMap>,
 }
 
 impl SourceFile {
@@ -327,7 +328,7 @@ impl fmt::Debug for SourceFile {
 #[unstable(feature = "proc_macro", issue = "38356")]
 impl PartialEq for SourceFile {
     fn eq(&self, other: &Self) -> bool {
-        Rc::ptr_eq(&self.filemap, &other.filemap)
+        Lrc::ptr_eq(&self.filemap, &other.filemap)
     }
 }
 
diff --git a/src/librustc/dep_graph/graph.rs b/src/librustc/dep_graph/graph.rs
index 96d6b0f79cfff..6dd525f79580c 100644
--- a/src/librustc/dep_graph/graph.rs
+++ b/src/librustc/dep_graph/graph.rs
@@ -13,10 +13,9 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
                                            StableHashingContextProvider};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
-use std::cell::{Ref, RefCell};
+use rustc_data_structures::sync::{Lrc, RwLock, ReadGuard, Lock};
 use std::env;
 use std::hash::Hash;
-use std::rc::Rc;
 use ty::TyCtxt;
 use util::common::{ProfileQueriesMsg, profq_msg};
 
@@ -32,7 +31,7 @@ use super::prev::PreviousDepGraph;
 
 #[derive(Clone)]
 pub struct DepGraph {
-    data: Option<Rc<DepGraphData>>,
+    data: Option<Lrc<DepGraphData>>,
 
     // At the moment we are using DepNode as key here. In the future it might
     // be possible to use an IndexVec<DepNodeIndex, _> here. At the moment there
@@ -41,7 +40,7 @@ pub struct DepGraph {
     //   we need to have a dep-graph to generate DepNodeIndices.
     // - The architecture is still in flux and it's not clear what how to best
     //   implement things.
-    fingerprints: Rc<RefCell<FxHashMap<DepNode, Fingerprint>>>
+    fingerprints: Lrc<Lock<FxHashMap<DepNode, Fingerprint>>>
 }
 
 
@@ -71,50 +70,50 @@ struct DepGraphData {
     /// tracking. The `current` field is the dependency graph of only the
     /// current compilation session: We don't merge the previous dep-graph into
     /// current one anymore.
-    current: RefCell<CurrentDepGraph>,
+    current: Lock<CurrentDepGraph>,
 
     /// The dep-graph from the previous compilation session. It contains all
     /// nodes and edges as well as all fingerprints of nodes that have them.
     previous: PreviousDepGraph,
 
-    colors: RefCell<FxHashMap<DepNode, DepNodeColor>>,
+    colors: Lock<FxHashMap<DepNode, DepNodeColor>>,
 
     /// When we load, there may be `.o` files, cached mir, or other such
     /// things available to us. If we find that they are not dirty, we
     /// load the path to the file storing those work-products here into
     /// this map. We can later look for and extract that data.
-    previous_work_products: RefCell<FxHashMap<WorkProductId, WorkProduct>>,
+    previous_work_products: RwLock<FxHashMap<WorkProductId, WorkProduct>>,
 
     /// Work-products that we generate in this run.
-    work_products: RefCell<FxHashMap<WorkProductId, WorkProduct>>,
+    work_products: RwLock<FxHashMap<WorkProductId, WorkProduct>>,
 
-    dep_node_debug: RefCell<FxHashMap<DepNode, String>>,
+    dep_node_debug: Lock<FxHashMap<DepNode, String>>,
 
     // Used for testing, only populated when -Zquery-dep-graph is specified.
-    loaded_from_cache: RefCell<FxHashMap<DepNodeIndex, bool>>,
+    loaded_from_cache: Lock<FxHashMap<DepNodeIndex, bool>>,
 }
 
 impl DepGraph {
 
     pub fn new(prev_graph: PreviousDepGraph) -> DepGraph {
         DepGraph {
-            data: Some(Rc::new(DepGraphData {
-                previous_work_products: RefCell::new(FxHashMap()),
-                work_products: RefCell::new(FxHashMap()),
-                dep_node_debug: RefCell::new(FxHashMap()),
-                current: RefCell::new(CurrentDepGraph::new()),
+            data: Some(Lrc::new(DepGraphData {
+                previous_work_products: RwLock::new(FxHashMap()),
+                work_products: RwLock::new(FxHashMap()),
+                dep_node_debug: Lock::new(FxHashMap()),
+                current: Lock::new(CurrentDepGraph::new()),
                 previous: prev_graph,
-                colors: RefCell::new(FxHashMap()),
-                loaded_from_cache: RefCell::new(FxHashMap()),
+                colors: Lock::new(FxHashMap()),
+                loaded_from_cache: Lock::new(FxHashMap()),
             })),
-            fingerprints: Rc::new(RefCell::new(FxHashMap())),
+            fingerprints: Lrc::new(Lock::new(FxHashMap())),
         }
     }
 
     pub fn new_disabled() -> DepGraph {
         DepGraph {
             data: None,
-            fingerprints: Rc::new(RefCell::new(FxHashMap())),
+            fingerprints: Lrc::new(Lock::new(FxHashMap())),
         }
     }
 
@@ -196,8 +195,8 @@ impl DepGraph {
                                     cx: C,
                                     arg: A,
                                     task: fn(C, A) -> R,
-                                    push: fn(&RefCell<CurrentDepGraph>, DepNode),
-                                    pop: fn(&RefCell<CurrentDepGraph>, DepNode) -> DepNodeIndex)
+                                    push: fn(&Lock<CurrentDepGraph>, DepNode),
+                                    pop: fn(&Lock<CurrentDepGraph>, DepNode) -> DepNodeIndex)
                                     -> (R, DepNodeIndex)
         where C: DepGraphSafe + StableHashingContextProvider<ContextType=HCX>,
               R: HashStable<HCX>,
@@ -384,13 +383,13 @@ impl DepGraph {
 
     /// Access the map of work-products created during this run. Only
     /// used during saving of the dep-graph.
-    pub fn work_products(&self) -> Ref<FxHashMap<WorkProductId, WorkProduct>> {
+    pub fn work_products(&self) -> ReadGuard<FxHashMap<WorkProductId, WorkProduct>> {
         self.data.as_ref().unwrap().work_products.borrow()
     }
 
     /// Access the map of work-products created during the cached run. Only
     /// used during saving of the dep-graph.
-    pub fn previous_work_products(&self) -> Ref<FxHashMap<WorkProductId, WorkProduct>> {
+    pub fn previous_work_products(&self) -> ReadGuard<FxHashMap<WorkProductId, WorkProduct>> {
         self.data.as_ref().unwrap().previous_work_products.borrow()
     }
 
diff --git a/src/librustc/dep_graph/raii.rs b/src/librustc/dep_graph/raii.rs
index 5728bcc7d2771..8bb8840836020 100644
--- a/src/librustc/dep_graph/raii.rs
+++ b/src/librustc/dep_graph/raii.rs
@@ -10,14 +10,14 @@
 
 use super::graph::CurrentDepGraph;
 
-use std::cell::RefCell;
+use rustc_data_structures::sync::Lock;
 
 pub struct IgnoreTask<'graph> {
-    graph: &'graph RefCell<CurrentDepGraph>,
+    graph: &'graph Lock<CurrentDepGraph>,
 }
 
 impl<'graph> IgnoreTask<'graph> {
-    pub(super) fn new(graph: &'graph RefCell<CurrentDepGraph>) -> IgnoreTask<'graph> {
+    pub(super) fn new(graph: &'graph Lock<CurrentDepGraph>) -> IgnoreTask<'graph> {
         graph.borrow_mut().push_ignore();
         IgnoreTask {
             graph,
diff --git a/src/librustc/hir/map/mod.rs b/src/librustc/hir/map/mod.rs
index 014e57716562c..84cb679303feb 100644
--- a/src/librustc/hir/map/mod.rs
+++ b/src/librustc/hir/map/mod.rs
@@ -29,9 +29,10 @@ use hir::print::Nested;
 use util::nodemap::{DefIdMap, FxHashMap};
 
 use arena::TypedArena;
-use std::cell::RefCell;
 use std::io;
 
+use rustc_data_structures::sync::Lock;
+
 pub mod blocks;
 mod collector;
 mod def_collector;
@@ -255,7 +256,7 @@ pub struct Map<'hir> {
     definitions: &'hir Definitions,
 
     /// Bodies inlined from other crates are cached here.
-    inlined_bodies: RefCell<DefIdMap<&'hir Body>>,
+    inlined_bodies: Lock<DefIdMap<&'hir Body>>,
 
     /// The reverse mapping of `node_to_hir_id`.
     hir_to_node_id: FxHashMap<HirId, NodeId>,
@@ -1090,7 +1091,7 @@ pub fn map_crate<'hir>(sess: &::session::Session,
         map,
         hir_to_node_id,
         definitions,
-        inlined_bodies: RefCell::new(DefIdMap()),
+        inlined_bodies: Lock::new(DefIdMap()),
     };
 
     hir_id_validator::check_crate(&map);
diff --git a/src/librustc/ich/caching_codemap_view.rs b/src/librustc/ich/caching_codemap_view.rs
index 3caf308d65268..e5bf384d253c5 100644
--- a/src/librustc/ich/caching_codemap_view.rs
+++ b/src/librustc/ich/caching_codemap_view.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::codemap::CodeMap;
 use syntax_pos::{BytePos, FileMap};
 
@@ -18,7 +18,7 @@ struct CacheEntry {
     line_number: usize,
     line_start: BytePos,
     line_end: BytePos,
-    file: Rc<FileMap>,
+    file: Lrc<FileMap>,
     file_index: usize,
 }
 
@@ -51,7 +51,7 @@ impl<'cm> CachingCodemapView<'cm> {
 
     pub fn byte_pos_to_line_and_col(&mut self,
                                     pos: BytePos)
-                                    -> Option<(Rc<FileMap>, usize, BytePos)> {
+                                    -> Option<(Lrc<FileMap>, usize, BytePos)> {
         self.time_stamp += 1;
 
         // Check if the position is in one of the cached lines
diff --git a/src/librustc/ich/hcx.rs b/src/librustc/ich/hcx.rs
index 2945b1ab91245..f9b1eee4bf796 100644
--- a/src/librustc/ich/hcx.rs
+++ b/src/librustc/ich/hcx.rs
@@ -357,6 +357,8 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Span {
             // Since the same expansion context is usually referenced many
             // times, we cache a stable hash of it and hash that instead of
             // recursing every time.
+            use std::cell::RefCell;
+            // FIXME: Move this to Session or a syntax_pos global
             thread_local! {
                 static CACHE: RefCell<FxHashMap<hygiene::Mark, u64>> =
                     RefCell::new(FxHashMap());
diff --git a/src/librustc/lint/context.rs b/src/librustc/lint/context.rs
index 32ab458cb91de..d60ee5f514678 100644
--- a/src/librustc/lint/context.rs
+++ b/src/librustc/lint/context.rs
@@ -27,6 +27,7 @@
 use self::TargetLint::*;
 
 use std::slice;
+use rustc_data_structures::sync::{RwLock, ReadGuard};
 use lint::{EarlyLintPassObject, LateLintPassObject};
 use lint::{Level, Lint, LintId, LintPass, LintBuffer};
 use lint::levels::{LintLevelSets, LintLevelsBuilder};
@@ -39,7 +40,6 @@ use ty::layout::{LayoutError, LayoutOf, TyLayout};
 use util::nodemap::FxHashMap;
 
 use std::default::Default as StdDefault;
-use std::cell::{Ref, RefCell};
 use syntax::ast;
 use syntax_pos::{MultiSpan, Span};
 use errors::DiagnosticBuilder;
@@ -77,7 +77,7 @@ pub struct LintStore {
 
 pub struct LintSession<'a, PassObject> {
     /// Reference to the store of registered lints.
-    lints: Ref<'a, LintStore>,
+    lints: ReadGuard<'a, LintStore>,
 
     /// Trait objects for each lint pass.
     passes: Option<Vec<PassObject>>,
@@ -317,7 +317,7 @@ impl<'a, PassObject: LintPassObject> LintSession<'a, PassObject> {
     /// Creates a new `LintSession`, by moving out the `LintStore`'s initial
     /// lint levels and pass objects. These can be restored using the `restore`
     /// method.
-    fn new(store: &'a RefCell<LintStore>) -> LintSession<'a, PassObject> {
+    fn new(store: &'a RwLock<LintStore>) -> LintSession<'a, PassObject> {
         let mut s = store.borrow_mut();
         let passes = PassObject::take_passes(&mut *s);
         drop(s);
@@ -328,7 +328,7 @@ impl<'a, PassObject: LintPassObject> LintSession<'a, PassObject> {
     }
 
     /// Restores the levels back to the original lint store.
-    fn restore(self, store: &RefCell<LintStore>) {
+    fn restore(self, store: &RwLock<LintStore>) {
         drop(self.lints);
         let mut s = store.borrow_mut();
         PassObject::restore_passes(&mut *s, self.passes);
diff --git a/src/librustc/lint/mod.rs b/src/librustc/lint/mod.rs
index f4abc54ad2e4e..42074d64d3c65 100644
--- a/src/librustc/lint/mod.rs
+++ b/src/librustc/lint/mod.rs
@@ -31,7 +31,7 @@
 pub use self::Level::*;
 pub use self::LintSource::*;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::{Send, Sync, Lrc};
 
 use errors::{DiagnosticBuilder, DiagnosticId};
 use hir::def_id::{CrateNum, LOCAL_CRATE};
@@ -257,8 +257,8 @@ pub trait EarlyLintPass: LintPass {
 }
 
 /// A lint pass boxed up as a trait object.
-pub type EarlyLintPassObject = Box<EarlyLintPass + 'static>;
-pub type LateLintPassObject = Box<for<'a, 'tcx> LateLintPass<'a, 'tcx> + 'static>;
+pub type EarlyLintPassObject = Box<EarlyLintPass + Send + Sync + 'static>;
+pub type LateLintPassObject = Box<for<'a, 'tcx> LateLintPass<'a, 'tcx> + Send + Sync + 'static>;
 
 /// Identifies a lint known to the compiler.
 #[derive(Clone, Copy, Debug)]
@@ -480,7 +480,7 @@ pub fn struct_lint_level<'a>(sess: &'a Session,
 }
 
 fn lint_levels<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, cnum: CrateNum)
-    -> Rc<LintLevelMap>
+    -> Lrc<LintLevelMap>
 {
     assert_eq!(cnum, LOCAL_CRATE);
     let mut builder = LintLevelMapBuilder {
@@ -493,7 +493,7 @@ fn lint_levels<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, cnum: CrateNum)
         intravisit::walk_crate(builder, krate);
     });
 
-    Rc::new(builder.levels.build_map())
+    Lrc::new(builder.levels.build_map())
 }
 
 struct LintLevelMapBuilder<'a, 'tcx: 'a> {
diff --git a/src/librustc/middle/cstore.rs b/src/librustc/middle/cstore.rs
index 9708afd204593..ea11930ae89d4 100644
--- a/src/librustc/middle/cstore.rs
+++ b/src/librustc/middle/cstore.rs
@@ -37,13 +37,12 @@ use util::nodemap::NodeSet;
 use std::any::Any;
 use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
-use std::rc::Rc;
-use rustc_data_structures::owning_ref::ErasedBoxRef;
 use syntax::ast;
 use syntax::ext::base::SyntaxExtension;
 use syntax::symbol::Symbol;
 use syntax_pos::Span;
 use rustc_back::target::Target;
+use rustc_data_structures::sync::{MetadataRef, Lrc};
 
 pub use self::NativeLibraryKind::*;
 
@@ -139,7 +138,7 @@ pub struct NativeLibrary {
 
 pub enum LoadedMacro {
     MacroDef(ast::Item),
-    ProcMacro(Rc<SyntaxExtension>),
+    ProcMacro(Lrc<SyntaxExtension>),
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -187,11 +186,11 @@ pub trait MetadataLoader {
     fn get_rlib_metadata(&self,
                          target: &Target,
                          filename: &Path)
-                         -> Result<ErasedBoxRef<[u8]>, String>;
+                         -> Result<MetadataRef, String>;
     fn get_dylib_metadata(&self,
                           target: &Target,
                           filename: &Path)
-                          -> Result<ErasedBoxRef<[u8]>, String>;
+                          -> Result<MetadataRef, String>;
 }
 
 #[derive(Clone)]
@@ -206,7 +205,7 @@ pub struct ExternConstBody<'tcx> {
 
 #[derive(Clone)]
 pub struct ExternBodyNestedBodies {
-    pub nested_bodies: Rc<BTreeMap<hir::BodyId, hir::Body>>,
+    pub nested_bodies: Lrc<BTreeMap<hir::BodyId, hir::Body>>,
 
     // It would require a lot of infrastructure to enable stable-hashing Bodies
     // from other crates, so we hash on export and just store the fingerprint
@@ -225,7 +224,7 @@ pub struct ExternBodyNestedBodies {
 /// (it'd break incremental compilation) and should only be called pre-HIR (e.g.
 /// during resolve)
 pub trait CrateStore {
-    fn crate_data_as_rc_any(&self, krate: CrateNum) -> Rc<Any>;
+    fn crate_data_as_rc_any(&self, krate: CrateNum) -> Lrc<Any>;
 
     // access to the metadata loader
     fn metadata_loader(&self) -> &MetadataLoader;
@@ -234,7 +233,7 @@ pub trait CrateStore {
     fn def_key(&self, def: DefId) -> DefKey;
     fn def_path(&self, def: DefId) -> hir_map::DefPath;
     fn def_path_hash(&self, def: DefId) -> hir_map::DefPathHash;
-    fn def_path_table(&self, cnum: CrateNum) -> Rc<DefPathTable>;
+    fn def_path_table(&self, cnum: CrateNum) -> Lrc<DefPathTable>;
 
     // "queries" used in resolve that aren't tracked for incremental compilation
     fn visibility_untracked(&self, def: DefId) -> ty::Visibility;
@@ -297,7 +296,7 @@ pub struct DummyCrateStore;
 
 #[allow(unused_variables)]
 impl CrateStore for DummyCrateStore {
-    fn crate_data_as_rc_any(&self, krate: CrateNum) -> Rc<Any>
+    fn crate_data_as_rc_any(&self, krate: CrateNum) -> Lrc<Any>
         { bug!("crate_data_as_rc_any") }
     // item info
     fn visibility_untracked(&self, def: DefId) -> ty::Visibility { bug!("visibility") }
@@ -325,7 +324,7 @@ impl CrateStore for DummyCrateStore {
     fn def_path_hash(&self, def: DefId) -> hir_map::DefPathHash {
         bug!("def_path_hash")
     }
-    fn def_path_table(&self, cnum: CrateNum) -> Rc<DefPathTable> {
+    fn def_path_table(&self, cnum: CrateNum) -> Lrc<DefPathTable> {
         bug!("def_path_table")
     }
     fn struct_field_names_untracked(&self, def: DefId) -> Vec<ast::Name> {
@@ -398,7 +397,7 @@ pub fn used_crates(tcx: TyCtxt, prefer: LinkagePreference)
         })
         .collect::<Vec<_>>();
     let mut ordering = tcx.postorder_cnums(LOCAL_CRATE);
-    Rc::make_mut(&mut ordering).reverse();
+    Lrc::make_mut(&mut ordering).reverse();
     libs.sort_by_key(|&(a, _)| {
         ordering.iter().position(|x| *x == a)
     });
diff --git a/src/librustc/middle/expr_use_visitor.rs b/src/librustc/middle/expr_use_visitor.rs
index 3bcde93fde502..02100514a5f6e 100644
--- a/src/librustc/middle/expr_use_visitor.rs
+++ b/src/librustc/middle/expr_use_visitor.rs
@@ -27,7 +27,7 @@ use middle::region;
 use ty::{self, TyCtxt, adjustment};
 
 use hir::{self, PatKind};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax::ptr::P;
 use syntax_pos::Span;
@@ -279,7 +279,7 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx, 'tcx> {
                param_env: ty::ParamEnv<'tcx>,
                region_scope_tree: &'a region::ScopeTree,
                tables: &'a ty::TypeckTables<'tcx>,
-               rvalue_promotable_map: Option<Rc<ItemLocalSet>>)
+               rvalue_promotable_map: Option<Lrc<ItemLocalSet>>)
                -> Self
     {
         ExprUseVisitor {
diff --git a/src/librustc/middle/mem_categorization.rs b/src/librustc/middle/mem_categorization.rs
index 0d4429de22a84..ce396276c98e2 100644
--- a/src/librustc/middle/mem_categorization.rs
+++ b/src/librustc/middle/mem_categorization.rs
@@ -85,6 +85,7 @@ use syntax::ast;
 use syntax_pos::Span;
 
 use std::fmt;
+use rustc_data_structures::sync::Lrc;
 use std::rc::Rc;
 use util::nodemap::ItemLocalSet;
 
@@ -286,7 +287,7 @@ pub struct MemCategorizationContext<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
     pub region_scope_tree: &'a region::ScopeTree,
     pub tables: &'a ty::TypeckTables<'tcx>,
-    rvalue_promotable_map: Option<Rc<ItemLocalSet>>,
+    rvalue_promotable_map: Option<Lrc<ItemLocalSet>>,
     infcx: Option<&'a InferCtxt<'a, 'gcx, 'tcx>>,
 }
 
@@ -395,7 +396,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx, 'tcx> {
     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                region_scope_tree: &'a region::ScopeTree,
                tables: &'a ty::TypeckTables<'tcx>,
-               rvalue_promotable_map: Option<Rc<ItemLocalSet>>)
+               rvalue_promotable_map: Option<Lrc<ItemLocalSet>>)
                -> MemCategorizationContext<'a, 'tcx, 'tcx> {
         MemCategorizationContext {
             tcx,
diff --git a/src/librustc/middle/reachable.rs b/src/librustc/middle/reachable.rs
index 6f457c9d1e1b2..5d61544f3c6b9 100644
--- a/src/librustc/middle/reachable.rs
+++ b/src/librustc/middle/reachable.rs
@@ -18,7 +18,7 @@
 use hir::map as hir_map;
 use hir::def::Def;
 use hir::def_id::{DefId, CrateNum};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use ty::{self, TyCtxt};
 use ty::maps::Providers;
 use middle::privacy;
@@ -378,7 +378,7 @@ impl<'a, 'tcx: 'a> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a,
 // We introduce a new-type here, so we can have a specialized HashStable
 // implementation for it.
 #[derive(Clone)]
-pub struct ReachableSet(pub Rc<NodeSet>);
+pub struct ReachableSet(pub Lrc<NodeSet>);
 
 
 fn reachable_set<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum) -> ReachableSet {
@@ -426,7 +426,7 @@ fn reachable_set<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum) ->
     reachable_context.propagate();
 
     // Return the set of reachable symbols.
-    ReachableSet(Rc::new(reachable_context.reachable_symbols))
+    ReachableSet(Lrc::new(reachable_context.reachable_symbols))
 }
 
 pub fn provide(providers: &mut Providers) {
diff --git a/src/librustc/middle/recursion_limit.rs b/src/librustc/middle/recursion_limit.rs
index 6c87f750376fa..85592353c8977 100644
--- a/src/librustc/middle/recursion_limit.rs
+++ b/src/librustc/middle/recursion_limit.rs
@@ -18,7 +18,7 @@
 use session::Session;
 use syntax::ast;
 
-use std::cell::Cell;
+use rustc_data_structures::sync::LockCell;
 
 pub fn update_limits(sess: &Session, krate: &ast::Crate) {
     update_limit(sess, krate, &sess.recursion_limit, "recursion_limit",
@@ -27,7 +27,7 @@ pub fn update_limits(sess: &Session, krate: &ast::Crate) {
                  "type length limit");
 }
 
-fn update_limit(sess: &Session, krate: &ast::Crate, limit: &Cell<usize>,
+fn update_limit(sess: &Session, krate: &ast::Crate, limit: &LockCell<usize>,
                 name: &str, description: &str) {
     for attr in &krate.attrs {
         if !attr.check_name(name) {
diff --git a/src/librustc/middle/region.rs b/src/librustc/middle/region.rs
index d3aa80e5585e2..d1feb8e9a07de 100644
--- a/src/librustc/middle/region.rs
+++ b/src/librustc/middle/region.rs
@@ -20,7 +20,7 @@ use ty;
 
 use std::fmt;
 use std::mem;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::codemap;
 use syntax::ast;
 use syntax_pos::{Span, DUMMY_SP};
@@ -1350,7 +1350,7 @@ impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
 }
 
 fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
-    -> Rc<ScopeTree>
+    -> Lrc<ScopeTree>
 {
     let closure_base_def_id = tcx.closure_base_def_id(def_id);
     if closure_base_def_id != def_id {
@@ -1392,7 +1392,7 @@ fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
         ScopeTree::default()
     };
 
-    Rc::new(scope_tree)
+    Lrc::new(scope_tree)
 }
 
 pub fn provide(providers: &mut Providers) {
diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
index 8b302dbe67a42..b3096703f8c2f 100644
--- a/src/librustc/middle/resolve_lifetime.rs
+++ b/src/librustc/middle/resolve_lifetime.rs
@@ -23,7 +23,7 @@ use ty::{self, TyCtxt};
 
 use std::cell::Cell;
 use std::mem::replace;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax::attr;
 use syntax::ptr::P;
@@ -212,10 +212,10 @@ struct NamedRegionMap {
 
 /// See `NamedRegionMap`.
 pub struct ResolveLifetimes {
-    defs: FxHashMap<LocalDefId, Rc<FxHashMap<ItemLocalId, Region>>>,
-    late_bound: FxHashMap<LocalDefId, Rc<FxHashSet<ItemLocalId>>>,
+    defs: FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Region>>>,
+    late_bound: FxHashMap<LocalDefId, Lrc<FxHashSet<ItemLocalId>>>,
     object_lifetime_defaults:
-        FxHashMap<LocalDefId, Rc<FxHashMap<ItemLocalId, Rc<Vec<ObjectLifetimeDefault>>>>>,
+        FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
 }
 
 impl_stable_hash_for!(struct ::middle::resolve_lifetime::ResolveLifetimes {
@@ -363,7 +363,7 @@ pub fn provide(providers: &mut ty::maps::Providers) {
 fn resolve_lifetimes<'tcx>(
     tcx: TyCtxt<'_, 'tcx, 'tcx>,
     for_krate: CrateNum,
-) -> Rc<ResolveLifetimes> {
+) -> Lrc<ResolveLifetimes> {
     assert_eq!(for_krate, LOCAL_CRATE);
 
     let named_region_map = krate(tcx);
@@ -372,29 +372,29 @@ fn resolve_lifetimes<'tcx>(
     for (k, v) in named_region_map.defs {
         let hir_id = tcx.hir.node_to_hir_id(k);
         let map = defs.entry(hir_id.owner_local_def_id())
-            .or_insert_with(|| Rc::new(FxHashMap()));
-        Rc::get_mut(map).unwrap().insert(hir_id.local_id, v);
+            .or_insert_with(|| Lrc::new(FxHashMap()));
+        Lrc::get_mut(map).unwrap().insert(hir_id.local_id, v);
     }
     let mut late_bound = FxHashMap();
     for k in named_region_map.late_bound {
         let hir_id = tcx.hir.node_to_hir_id(k);
         let map = late_bound
             .entry(hir_id.owner_local_def_id())
-            .or_insert_with(|| Rc::new(FxHashSet()));
-        Rc::get_mut(map).unwrap().insert(hir_id.local_id);
+            .or_insert_with(|| Lrc::new(FxHashSet()));
+        Lrc::get_mut(map).unwrap().insert(hir_id.local_id);
     }
     let mut object_lifetime_defaults = FxHashMap();
     for (k, v) in named_region_map.object_lifetime_defaults {
         let hir_id = tcx.hir.node_to_hir_id(k);
         let map = object_lifetime_defaults
             .entry(hir_id.owner_local_def_id())
-            .or_insert_with(|| Rc::new(FxHashMap()));
-        Rc::get_mut(map)
+            .or_insert_with(|| Lrc::new(FxHashMap()));
+        Lrc::get_mut(map)
             .unwrap()
-            .insert(hir_id.local_id, Rc::new(v));
+            .insert(hir_id.local_id, Lrc::new(v));
     }
 
-    Rc::new(ResolveLifetimes {
+    Lrc::new(ResolveLifetimes {
         defs,
         late_bound,
         object_lifetime_defaults,
diff --git a/src/librustc/mir/cache.rs b/src/librustc/mir/cache.rs
index efc2f647cfdf5..8fed58a178862 100644
--- a/src/librustc/mir/cache.rs
+++ b/src/librustc/mir/cache.rs
@@ -8,8 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::cell::{Ref, RefCell};
 use rustc_data_structures::indexed_vec::IndexVec;
+use rustc_data_structures::sync::{RwLock, ReadGuard};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
                                            StableHasherResult};
 use ich::StableHashingContext;
@@ -19,7 +19,7 @@ use rustc_serialize as serialize;
 
 #[derive(Clone, Debug)]
 pub struct Cache {
-    predecessors: RefCell<Option<IndexVec<BasicBlock, Vec<BasicBlock>>>>
+    predecessors: RwLock<Option<IndexVec<BasicBlock, Vec<BasicBlock>>>>
 }
 
 
@@ -46,7 +46,7 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Cache {
 impl Cache {
     pub fn new() -> Self {
         Cache {
-            predecessors: RefCell::new(None)
+            predecessors: RwLock::new(None)
         }
     }
 
@@ -55,12 +55,12 @@ impl Cache {
         *self.predecessors.borrow_mut() = None;
     }
 
-    pub fn predecessors(&self, mir: &Mir) -> Ref<IndexVec<BasicBlock, Vec<BasicBlock>>> {
+    pub fn predecessors(&self, mir: &Mir) -> ReadGuard<IndexVec<BasicBlock, Vec<BasicBlock>>> {
         if self.predecessors.borrow().is_none() {
             *self.predecessors.borrow_mut() = Some(calculate_predecessors(mir));
         }
 
-        Ref::map(self.predecessors.borrow(), |p| p.as_ref().unwrap())
+        ReadGuard::map(self.predecessors.borrow(), |p| p.as_ref().unwrap())
     }
 }
 
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index f410865a6cd7f..ba0b19f7df274 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -14,6 +14,7 @@ use graphviz::IntoCow;
 use middle::const_val::ConstVal;
 use middle::region;
 use rustc_const_math::{ConstUsize, ConstInt, ConstMathErr};
+use rustc_data_structures::sync::{Lrc};
 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 use rustc_data_structures::control_flow_graph::dominators::{Dominators, dominators};
 use rustc_data_structures::control_flow_graph::{GraphPredecessors, GraphSuccessors};
@@ -30,11 +31,10 @@ use std::slice;
 use hir::{self, InlineAsm};
 use std::ascii;
 use std::borrow::{Cow};
-use std::cell::Ref;
+use rustc_data_structures::sync::ReadGuard;
 use std::fmt::{self, Debug, Formatter, Write};
 use std::{iter, u32};
 use std::ops::{Index, IndexMut};
-use std::rc::Rc;
 use std::vec::IntoIter;
 use syntax::ast::{self, Name};
 use syntax::symbol::InternedString;
@@ -184,13 +184,13 @@ impl<'tcx> Mir<'tcx> {
     }
 
     #[inline]
-    pub fn predecessors(&self) -> Ref<IndexVec<BasicBlock, Vec<BasicBlock>>> {
+    pub fn predecessors(&self) -> ReadGuard<IndexVec<BasicBlock, Vec<BasicBlock>>> {
         self.cache.predecessors(self)
     }
 
     #[inline]
-    pub fn predecessors_for(&self, bb: BasicBlock) -> Ref<Vec<BasicBlock>> {
-        Ref::map(self.predecessors(), |p| &p[bb])
+    pub fn predecessors_for(&self, bb: BasicBlock) -> ReadGuard<Vec<BasicBlock>> {
+        ReadGuard::map(self.predecessors(), |p| &p[bb])
     }
 
     #[inline]
@@ -1788,10 +1788,10 @@ pub struct UnsafetyViolation {
 #[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub struct UnsafetyCheckResult {
     /// Violations that are propagated *upwards* from this function
-    pub violations: Rc<[UnsafetyViolation]>,
+    pub violations: Lrc<[UnsafetyViolation]>,
     /// unsafe blocks in this function, along with whether they are used. This is
     /// used for the "unused_unsafe" lint.
-    pub unsafe_blocks: Rc<[(ast::NodeId, bool)]>,
+    pub unsafe_blocks: Lrc<[(ast::NodeId, bool)]>,
 }
 
 /// The layout of generator state
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 0de1c20dbde1e..c7f1e0da91e73 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -23,6 +23,8 @@ use ty::tls;
 use util::nodemap::{FxHashMap, FxHashSet};
 use util::common::{duration_to_secs_str, ErrorReported};
 
+use rustc_data_structures::sync::{self, Lrc, RwLock, Lock, LockCell, ReadGuard};
+
 use syntax::ast::NodeId;
 use errors::{self, DiagnosticBuilder, DiagnosticId};
 use errors::emitter::{Emitter, EmitterWriter};
@@ -39,13 +41,11 @@ use rustc_back::target::Target;
 use rustc_data_structures::flock;
 use jobserver::Client;
 
-use std::cell::{self, Cell, RefCell};
 use std::collections::HashMap;
 use std::env;
 use std::fmt;
 use std::io::Write;
 use std::path::{Path, PathBuf};
-use std::rc::Rc;
 use std::sync::{Once, ONCE_INIT};
 use std::time::Duration;
 
@@ -62,10 +62,10 @@ pub struct Session {
     pub opts: config::Options,
     pub parse_sess: ParseSess,
     /// For a library crate, this is always none
-    pub entry_fn: RefCell<Option<(NodeId, Span)>>,
-    pub entry_type: Cell<Option<config::EntryFnType>>,
-    pub plugin_registrar_fn: Cell<Option<ast::NodeId>>,
-    pub derive_registrar_fn: Cell<Option<ast::NodeId>>,
+    pub entry_fn: Lock<Option<(NodeId, Span)>>,
+    pub entry_type: LockCell<Option<config::EntryFnType>>,
+    pub plugin_registrar_fn: LockCell<Option<ast::NodeId>>,
+    pub derive_registrar_fn: LockCell<Option<ast::NodeId>>,
     pub default_sysroot: Option<PathBuf>,
     /// The name of the root source file of the crate, in the local file system.
     /// `None` means that there is no source file.
@@ -73,88 +73,88 @@ pub struct Session {
     /// The directory the compiler has been executed in plus a flag indicating
     /// if the value stored here has been affected by path remapping.
     pub working_dir: (PathBuf, bool),
-    pub lint_store: RefCell<lint::LintStore>,
-    pub buffered_lints: RefCell<Option<lint::LintBuffer>>,
+    pub lint_store: RwLock<lint::LintStore>,
+    pub buffered_lints: Lock<Option<lint::LintBuffer>>,
     /// Set of (DiagnosticId, Option<Span>, message) tuples tracking
     /// (sub)diagnostics that have been set once, but should not be set again,
     /// in order to avoid redundantly verbose output (Issue #24690, #44953).
-    pub one_time_diagnostics: RefCell<FxHashSet<(DiagnosticMessageId, Option<Span>, String)>>,
-    pub plugin_llvm_passes: RefCell<Vec<String>>,
-    pub plugin_attributes: RefCell<Vec<(String, AttributeType)>>,
-    pub crate_types: RefCell<Vec<config::CrateType>>,
-    pub dependency_formats: RefCell<dependency_format::Dependencies>,
+    pub one_time_diagnostics: Lock<FxHashSet<(DiagnosticMessageId, Option<Span>, String)>>,
+    pub plugin_llvm_passes: Lock<Vec<String>>,
+    pub plugin_attributes: Lock<Vec<(String, AttributeType)>>,
+    pub crate_types: RwLock<Vec<config::CrateType>>,
+    pub dependency_formats: Lock<dependency_format::Dependencies>,
         /// The crate_disambiguator is constructed out of all the `-C metadata`
     /// arguments passed to the compiler. Its value together with the crate-name
     /// forms a unique global identifier for the crate. It is used to allow
     /// multiple crates with the same name to coexist. See the
     /// trans::back::symbol_names module for more information.
-    pub crate_disambiguator: RefCell<Option<CrateDisambiguator>>,
-    pub features: RefCell<feature_gate::Features>,
+    pub crate_disambiguator: Lock<Option<CrateDisambiguator>>,
+    pub features: RwLock<feature_gate::Features>,
 
     /// The maximum recursion limit for potentially infinitely recursive
     /// operations such as auto-dereference and monomorphization.
-    pub recursion_limit: Cell<usize>,
+    pub recursion_limit: LockCell<usize>,
 
     /// The maximum length of types during monomorphization.
-    pub type_length_limit: Cell<usize>,
+    pub type_length_limit: LockCell<usize>,
 
     /// The metadata::creader module may inject an allocator/panic_runtime
     /// dependency if it didn't already find one, and this tracks what was
     /// injected.
-    pub injected_allocator: Cell<Option<CrateNum>>,
-    pub allocator_kind: Cell<Option<AllocatorKind>>,
-    pub injected_panic_runtime: Cell<Option<CrateNum>>,
+    pub injected_allocator: LockCell<Option<CrateNum>>,
+    pub allocator_kind: LockCell<Option<AllocatorKind>>,
+    pub injected_panic_runtime: LockCell<Option<CrateNum>>,
 
     /// Map from imported macro spans (which consist of
     /// the localized span for the macro body) to the
     /// macro name and definition span in the source crate.
-    pub imported_macro_spans: RefCell<HashMap<Span, (String, Span)>>,
+    pub imported_macro_spans: Lock<HashMap<Span, (String, Span)>>,
 
-    incr_comp_session: RefCell<IncrCompSession>,
+    incr_comp_session: RwLock<IncrCompSession>,
 
     /// Some measurements that are being gathered during compilation.
     pub perf_stats: PerfStats,
 
     /// Data about code being compiled, gathered during compilation.
-    pub code_stats: RefCell<CodeStats>,
+    pub code_stats: Lock<CodeStats>,
 
-    next_node_id: Cell<ast::NodeId>,
+    next_node_id: LockCell<ast::NodeId>,
 
     /// If -zfuel=crate=n is specified, Some(crate).
     optimization_fuel_crate: Option<String>,
     /// If -zfuel=crate=n is specified, initially set to n. Otherwise 0.
-    optimization_fuel_limit: Cell<u64>,
+    optimization_fuel_limit: LockCell<u64>,
     /// We're rejecting all further optimizations.
-    out_of_fuel: Cell<bool>,
+    out_of_fuel: LockCell<bool>,
 
     // The next two are public because the driver needs to read them.
 
     /// If -zprint-fuel=crate, Some(crate).
     pub print_fuel_crate: Option<String>,
     /// Always set to zero and incremented so that we can print fuel expended by a crate.
-    pub print_fuel: Cell<u64>,
+    pub print_fuel: LockCell<u64>,
 
     /// Loaded up early on in the initialization of this `Session` to avoid
     /// false positives about a job server in our environment.
     pub jobserver_from_env: Option<Client>,
 
     /// Metadata about the allocators for the current crate being compiled
-    pub has_global_allocator: Cell<bool>,
+    pub has_global_allocator: LockCell<bool>,
 }
 
 pub struct PerfStats {
     /// The accumulated time needed for computing the SVH of the crate
-    pub svh_time: Cell<Duration>,
+    pub svh_time: LockCell<Duration>,
     /// The accumulated time spent on computing incr. comp. hashes
-    pub incr_comp_hashes_time: Cell<Duration>,
+    pub incr_comp_hashes_time: LockCell<Duration>,
     /// The number of incr. comp. hash computations performed
-    pub incr_comp_hashes_count: Cell<u64>,
+    pub incr_comp_hashes_count: LockCell<u64>,
     /// The number of bytes hashed when computing ICH values
-    pub incr_comp_bytes_hashed: Cell<u64>,
+    pub incr_comp_bytes_hashed: LockCell<u64>,
     /// The accumulated time spent on computing symbol hashes
-    pub symbol_hash_time: Cell<Duration>,
+    pub symbol_hash_time: LockCell<Duration>,
     /// The accumulated time spent decoding def path tables from metadata
-    pub decode_def_path_tables_time: Cell<Duration>,
+    pub decode_def_path_tables_time: LockCell<Duration>,
 }
 
 /// Enum to support dispatch of one-time diagnostics (in Session.diag_once)
@@ -652,9 +652,9 @@ impl Session {
         };
     }
 
-    pub fn incr_comp_session_dir(&self) -> cell::Ref<PathBuf> {
+    pub fn incr_comp_session_dir(&self) -> ReadGuard<PathBuf> {
         let incr_comp_session = self.incr_comp_session.borrow();
-        cell::Ref::map(incr_comp_session, |incr_comp_session| {
+        ReadGuard::map(incr_comp_session, |incr_comp_session| {
             match *incr_comp_session {
                 IncrCompSession::NotInitialized => {
                     bug!("Trying to get session directory from IncrCompSession `{:?}`",
@@ -669,7 +669,7 @@ impl Session {
         })
     }
 
-    pub fn incr_comp_session_dir_opt(&self) -> Option<cell::Ref<PathBuf>> {
+    pub fn incr_comp_session_dir_opt(&self) -> Option<ReadGuard<PathBuf>> {
         if self.opts.incremental.is_some() {
             Some(self.incr_comp_session_dir())
         } else {
@@ -839,14 +839,14 @@ pub fn build_session(sopts: config::Options,
     build_session_with_codemap(sopts,
                                local_crate_source_file,
                                registry,
-                               Rc::new(codemap::CodeMap::new(file_path_mapping)),
+                               Lrc::new(codemap::CodeMap::new(file_path_mapping)),
                                None)
 }
 
 pub fn build_session_with_codemap(sopts: config::Options,
                                   local_crate_source_file: Option<PathBuf>,
                                   registry: errors::registry::Registry,
-                                  codemap: Rc<codemap::CodeMap>,
+                                  codemap: Lrc<codemap::CodeMap>,
                                   emitter_dest: Option<Box<Write + Send>>)
                                   -> Session {
     // FIXME: This is not general enough to make the warning lint completely override
@@ -866,7 +866,7 @@ pub fn build_session_with_codemap(sopts: config::Options,
 
     let external_macro_backtrace = sopts.debugging_opts.external_macro_backtrace;
 
-    let emitter: Box<Emitter> = match (sopts.error_format, emitter_dest) {
+    let emitter: Box<Emitter + sync::Send> = match (sopts.error_format, emitter_dest) {
         (config::ErrorOutputType::HumanReadable(color_config), None) => {
             Box::new(EmitterWriter::stderr(color_config, Some(codemap.clone()), false))
         }
@@ -906,7 +906,7 @@ pub fn build_session_with_codemap(sopts: config::Options,
 pub fn build_session_(sopts: config::Options,
                       local_crate_source_file: Option<PathBuf>,
                       span_diagnostic: errors::Handler,
-                      codemap: Rc<codemap::CodeMap>)
+                      codemap: Lrc<codemap::CodeMap>)
                       -> Session {
     let host = match Target::search(config::host_triple()) {
         Ok(t) => t,
@@ -929,10 +929,10 @@ pub fn build_session_(sopts: config::Options,
     });
 
     let optimization_fuel_crate = sopts.debugging_opts.fuel.as_ref().map(|i| i.0.clone());
-    let optimization_fuel_limit = Cell::new(sopts.debugging_opts.fuel.as_ref()
+    let optimization_fuel_limit = LockCell::new(sopts.debugging_opts.fuel.as_ref()
         .map(|i| i.1).unwrap_or(0));
     let print_fuel_crate = sopts.debugging_opts.print_fuel.clone();
-    let print_fuel = Cell::new(0);
+    let print_fuel = LockCell::new(0);
 
     let working_dir = match env::current_dir() {
         Ok(dir) => dir,
@@ -948,44 +948,44 @@ pub fn build_session_(sopts: config::Options,
         opts: sopts,
         parse_sess: p_s,
         // For a library crate, this is always none
-        entry_fn: RefCell::new(None),
-        entry_type: Cell::new(None),
-        plugin_registrar_fn: Cell::new(None),
-        derive_registrar_fn: Cell::new(None),
+        entry_fn: Lock::new(None),
+        entry_type: LockCell::new(None),
+        plugin_registrar_fn: LockCell::new(None),
+        derive_registrar_fn: LockCell::new(None),
         default_sysroot,
         local_crate_source_file,
         working_dir,
-        lint_store: RefCell::new(lint::LintStore::new()),
-        buffered_lints: RefCell::new(Some(lint::LintBuffer::new())),
-        one_time_diagnostics: RefCell::new(FxHashSet()),
-        plugin_llvm_passes: RefCell::new(Vec::new()),
-        plugin_attributes: RefCell::new(Vec::new()),
-        crate_types: RefCell::new(Vec::new()),
-        dependency_formats: RefCell::new(FxHashMap()),
-        crate_disambiguator: RefCell::new(None),
-        features: RefCell::new(feature_gate::Features::new()),
-        recursion_limit: Cell::new(64),
-        type_length_limit: Cell::new(1048576),
-        next_node_id: Cell::new(NodeId::new(1)),
-        injected_allocator: Cell::new(None),
-        allocator_kind: Cell::new(None),
-        injected_panic_runtime: Cell::new(None),
-        imported_macro_spans: RefCell::new(HashMap::new()),
-        incr_comp_session: RefCell::new(IncrCompSession::NotInitialized),
+        lint_store: RwLock::new(lint::LintStore::new()),
+        buffered_lints: Lock::new(Some(lint::LintBuffer::new())),
+        one_time_diagnostics: Lock::new(FxHashSet()),
+        plugin_llvm_passes: Lock::new(Vec::new()),
+        plugin_attributes: Lock::new(Vec::new()),
+        crate_types: RwLock::new(Vec::new()),
+        dependency_formats: Lock::new(FxHashMap()),
+        crate_disambiguator: Lock::new(None),
+        features: RwLock::new(feature_gate::Features::new()),
+        recursion_limit: LockCell::new(64),
+        type_length_limit: LockCell::new(1048576),
+        next_node_id: LockCell::new(NodeId::new(1)),
+        injected_allocator: LockCell::new(None),
+        allocator_kind: LockCell::new(None),
+        injected_panic_runtime: LockCell::new(None),
+        imported_macro_spans: Lock::new(HashMap::new()),
+        incr_comp_session: RwLock::new(IncrCompSession::NotInitialized),
         perf_stats: PerfStats {
-            svh_time: Cell::new(Duration::from_secs(0)),
-            incr_comp_hashes_time: Cell::new(Duration::from_secs(0)),
-            incr_comp_hashes_count: Cell::new(0),
-            incr_comp_bytes_hashed: Cell::new(0),
-            symbol_hash_time: Cell::new(Duration::from_secs(0)),
-            decode_def_path_tables_time: Cell::new(Duration::from_secs(0)),
+            svh_time: LockCell::new(Duration::from_secs(0)),
+            incr_comp_hashes_time: LockCell::new(Duration::from_secs(0)),
+            incr_comp_hashes_count: LockCell::new(0),
+            incr_comp_bytes_hashed: LockCell::new(0),
+            symbol_hash_time: LockCell::new(Duration::from_secs(0)),
+            decode_def_path_tables_time: LockCell::new(Duration::from_secs(0)),
         },
-        code_stats: RefCell::new(CodeStats::new()),
+        code_stats: Lock::new(CodeStats::new()),
         optimization_fuel_crate,
         optimization_fuel_limit,
         print_fuel_crate,
         print_fuel,
-        out_of_fuel: Cell::new(false),
+        out_of_fuel: LockCell::new(false),
         // Note that this is unsafe because it may misinterpret file descriptors
         // on Unix as jobserver file descriptors. We hopefully execute this near
         // the beginning of the process though to ensure we don't get false
@@ -1003,7 +1003,7 @@ pub fn build_session_(sopts: config::Options,
             });
             (*GLOBAL_JOBSERVER).clone()
         },
-        has_global_allocator: Cell::new(false),
+        has_global_allocator: LockCell::new(false),
     };
 
     sess
@@ -1056,7 +1056,7 @@ pub enum IncrCompSession {
 }
 
 pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
-    let emitter: Box<Emitter> = match output {
+    let emitter: Box<Emitter + sync::Send> = match output {
         config::ErrorOutputType::HumanReadable(color_config) => {
             Box::new(EmitterWriter::stderr(color_config, None, false))
         }
@@ -1071,7 +1071,7 @@ pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
 }
 
 pub fn early_warn(output: config::ErrorOutputType, msg: &str) {
-    let emitter: Box<Emitter> = match output {
+    let emitter: Box<Emitter + sync::Send> = match output {
         config::ErrorOutputType::HumanReadable(color_config) => {
             Box::new(EmitterWriter::stderr(color_config, None, false))
         }
diff --git a/src/librustc/traits/mod.rs b/src/librustc/traits/mod.rs
index 94605d895a554..c7bef6c6e2c6b 100644
--- a/src/librustc/traits/mod.rs
+++ b/src/librustc/traits/mod.rs
@@ -25,6 +25,7 @@ use ty::{self, AdtKind, Ty, TyCtxt, TypeFoldable, ToPredicate};
 use ty::error::{ExpectedFound, TypeError};
 use infer::{InferCtxt};
 
+use rustc_data_structures::sync::Lrc;
 use std::rc::Rc;
 use syntax::ast;
 use syntax_pos::{Span, DUMMY_SP};
@@ -693,11 +694,11 @@ pub fn normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 fn vtable_methods<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>)
-    -> Rc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>
+    -> Lrc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>
 {
     debug!("vtable_methods({:?})", trait_ref);
 
-    Rc::new(
+    Lrc::new(
         supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
             let trait_methods = tcx.associated_items(trait_ref.def_id())
                 .filter(|item| item.kind == ty::AssociatedKind::Method);
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index e70de0e566e41..c724db448a8eb 100644
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -41,10 +41,10 @@ use ty::fast_reject;
 use ty::relate::TypeRelation;
 use middle::lang_items;
 
+use rustc_data_structures::sync::Lock;
 use rustc_data_structures::bitvec::BitVector;
 use rustc_data_structures::snapshot_vec::{SnapshotVecDelegate, SnapshotVec};
 use std::iter;
-use std::cell::RefCell;
 use std::cmp;
 use std::fmt;
 use std::marker::PhantomData;
@@ -148,7 +148,7 @@ struct TraitObligationStack<'prev, 'tcx: 'prev> {
 
 #[derive(Clone)]
 pub struct SelectionCache<'tcx> {
-    hashmap: RefCell<FxHashMap<ty::TraitRef<'tcx>,
+    hashmap: Lock<FxHashMap<ty::TraitRef<'tcx>,
                                WithDepNode<SelectionResult<'tcx, SelectionCandidate<'tcx>>>>>,
 }
 
@@ -413,7 +413,7 @@ impl EvaluationResult {
 
 #[derive(Clone)]
 pub struct EvaluationCache<'tcx> {
-    hashmap: RefCell<FxHashMap<ty::PolyTraitRef<'tcx>, WithDepNode<EvaluationResult>>>
+    hashmap: Lock<FxHashMap<ty::PolyTraitRef<'tcx>, WithDepNode<EvaluationResult>>>
 }
 
 impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
@@ -3303,7 +3303,7 @@ impl<'tcx> TraitObligation<'tcx> {
 impl<'tcx> SelectionCache<'tcx> {
     pub fn new() -> SelectionCache<'tcx> {
         SelectionCache {
-            hashmap: RefCell::new(FxHashMap())
+            hashmap: Lock::new(FxHashMap())
         }
     }
 }
@@ -3311,7 +3311,7 @@ impl<'tcx> SelectionCache<'tcx> {
 impl<'tcx> EvaluationCache<'tcx> {
     pub fn new() -> EvaluationCache<'tcx> {
         EvaluationCache {
-            hashmap: RefCell::new(FxHashMap())
+            hashmap: Lock::new(FxHashMap())
         }
     }
 }
diff --git a/src/librustc/traits/specialize/mod.rs b/src/librustc/traits/specialize/mod.rs
index afe29cc0e7baf..7973aae979b8b 100644
--- a/src/librustc/traits/specialize/mod.rs
+++ b/src/librustc/traits/specialize/mod.rs
@@ -28,7 +28,7 @@ use traits::{self, Reveal, ObligationCause};
 use traits::select::IntercrateAmbiguityCause;
 use ty::{self, TyCtxt, TypeFoldable};
 use syntax_pos::DUMMY_SP;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use lint;
 
@@ -306,7 +306,7 @@ impl SpecializesCache {
 // Query provider for `specialization_graph_of`.
 pub(super) fn specialization_graph_provider<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                       trait_id: DefId)
-                                                      -> Rc<specialization_graph::Graph> {
+                                                      -> Lrc<specialization_graph::Graph> {
     let mut sg = specialization_graph::Graph::new();
 
     let mut trait_impls = Vec::new();
@@ -390,7 +390,7 @@ pub(super) fn specialization_graph_provider<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx
         }
     }
 
-    Rc::new(sg)
+    Lrc::new(sg)
 }
 
 /// Recovers the "impl X for Y" signature from `impl_def_id` and returns it as a
diff --git a/src/librustc/traits/specialize/specialization_graph.rs b/src/librustc/traits/specialize/specialization_graph.rs
index 834389e5d009c..e55d4614a2ee3 100644
--- a/src/librustc/traits/specialize/specialization_graph.rs
+++ b/src/librustc/traits/specialize/specialization_graph.rs
@@ -17,7 +17,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
 use traits;
 use ty::{self, TyCtxt, TypeFoldable};
 use ty::fast_reject::{self, SimplifiedType};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast::Name;
 use util::nodemap::{DefIdMap, FxHashMap};
 
@@ -330,7 +330,7 @@ impl<'a, 'gcx, 'tcx> Node {
 
 pub struct Ancestors {
     trait_def_id: DefId,
-    specialization_graph: Rc<Graph>,
+    specialization_graph: Lrc<Graph>,
     current_source: Option<Node>,
 }
 
diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index b233156cf7fc6..9475e45f52e74 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -55,16 +55,15 @@ use rustc_data_structures::stable_hasher::{HashStable, hash_stable_hashmap,
 use arena::{TypedArena, DroplessArena};
 use rustc_const_math::{ConstInt, ConstUsize};
 use rustc_data_structures::indexed_vec::IndexVec;
+use rustc_data_structures::sync::{Sync, Lrc, Lock, LockCell};
 use std::any::Any;
 use std::borrow::Borrow;
-use std::cell::{Cell, RefCell};
 use std::cmp::Ordering;
 use std::collections::hash_map::{self, Entry};
 use std::hash::{Hash, Hasher};
 use std::mem;
 use std::ops::Deref;
 use std::iter;
-use std::rc::Rc;
 use std::sync::mpsc;
 use std::sync::Arc;
 use syntax::abi;
@@ -127,26 +126,26 @@ pub struct CtxtInterners<'tcx> {
 
     /// Specifically use a speedy hash algorithm for these hash sets,
     /// they're accessed quite often.
-    type_: RefCell<FxHashSet<Interned<'tcx, TyS<'tcx>>>>,
-    type_list: RefCell<FxHashSet<Interned<'tcx, Slice<Ty<'tcx>>>>>,
-    substs: RefCell<FxHashSet<Interned<'tcx, Substs<'tcx>>>>,
-    region: RefCell<FxHashSet<Interned<'tcx, RegionKind>>>,
-    existential_predicates: RefCell<FxHashSet<Interned<'tcx, Slice<ExistentialPredicate<'tcx>>>>>,
-    predicates: RefCell<FxHashSet<Interned<'tcx, Slice<Predicate<'tcx>>>>>,
-    const_: RefCell<FxHashSet<Interned<'tcx, Const<'tcx>>>>,
+    type_: Lock<FxHashSet<Interned<'tcx, TyS<'tcx>>>>,
+    type_list: Lock<FxHashSet<Interned<'tcx, Slice<Ty<'tcx>>>>>,
+    substs: Lock<FxHashSet<Interned<'tcx, Substs<'tcx>>>>,
+    region: Lock<FxHashSet<Interned<'tcx, RegionKind>>>,
+    existential_predicates: Lock<FxHashSet<Interned<'tcx, Slice<ExistentialPredicate<'tcx>>>>>,
+    predicates: Lock<FxHashSet<Interned<'tcx, Slice<Predicate<'tcx>>>>>,
+    const_: Lock<FxHashSet<Interned<'tcx, Const<'tcx>>>>,
 }
 
 impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
     fn new(arena: &'tcx DroplessArena) -> CtxtInterners<'tcx> {
         CtxtInterners {
-            arena,
-            type_: RefCell::new(FxHashSet()),
-            type_list: RefCell::new(FxHashSet()),
-            substs: RefCell::new(FxHashSet()),
-            region: RefCell::new(FxHashSet()),
-            existential_predicates: RefCell::new(FxHashSet()),
-            predicates: RefCell::new(FxHashSet()),
-            const_: RefCell::new(FxHashSet()),
+            arena: arena,
+            type_: Lock::new(FxHashSet()),
+            type_list: Lock::new(FxHashSet()),
+            substs: Lock::new(FxHashSet()),
+            region: Lock::new(FxHashSet()),
+            existential_predicates: Lock::new(FxHashSet()),
+            predicates: Lock::new(FxHashSet()),
+            const_: Lock::new(FxHashSet()),
         }
     }
 
@@ -397,9 +396,9 @@ pub struct TypeckTables<'tcx> {
 
     /// Set of trait imports actually used in the method resolution.
     /// This is used for warning unused imports. During type
-    /// checking, this `Rc` should not be cloned: it must have a ref-count
+    /// checking, this `Lrc` should not be cloned: it must have a ref-count
     /// of 1 so that we can insert things into the set mutably.
-    pub used_trait_imports: Rc<DefIdSet>,
+    pub used_trait_imports: Lrc<DefIdSet>,
 
     /// If any errors occurred while type-checking this body,
     /// this field will be set to `true`.
@@ -426,7 +425,7 @@ impl<'tcx> TypeckTables<'tcx> {
             liberated_fn_sigs: ItemLocalMap(),
             fru_field_types: ItemLocalMap(),
             cast_kinds: ItemLocalMap(),
-            used_trait_imports: Rc::new(DefIdSet()),
+            used_trait_imports: Lrc::new(DefIdSet()),
             tainted_by_errors: false,
             free_region_map: FreeRegionMap::new(),
         }
@@ -797,7 +796,7 @@ pub struct GlobalCtxt<'tcx> {
     global_arenas: &'tcx GlobalArenas<'tcx>,
     global_interners: CtxtInterners<'tcx>,
 
-    cstore: &'tcx CrateStore,
+    cstore: &'tcx (CrateStore + Sync),
 
     pub sess: &'tcx Session,
 
@@ -814,11 +813,11 @@ pub struct GlobalCtxt<'tcx> {
     /// Map indicating what traits are in scope for places where this
     /// is relevant; generated by resolve.
     trait_map: FxHashMap<DefIndex,
-                         Rc<FxHashMap<ItemLocalId,
-                                      Rc<StableVec<TraitCandidate>>>>>,
+                         Lrc<FxHashMap<ItemLocalId,
+                                       Lrc<StableVec<TraitCandidate>>>>>,
 
     /// Export map produced by name resolution.
-    export_map: FxHashMap<DefId, Rc<Vec<Export>>>,
+    export_map: FxHashMap<DefId, Lrc<Vec<Export>>>,
 
     pub hir: hir_map::Map<'tcx>,
 
@@ -831,14 +830,14 @@ pub struct GlobalCtxt<'tcx> {
     // Records the free variables refrenced by every closure
     // expression. Do not track deps for this, just recompute it from
     // scratch every time.
-    freevars: FxHashMap<DefId, Rc<Vec<hir::Freevar>>>,
+    freevars: FxHashMap<DefId, Lrc<Vec<hir::Freevar>>>,
 
     maybe_unused_trait_imports: FxHashSet<DefId>,
 
     maybe_unused_extern_crates: Vec<(DefId, Span)>,
 
     // Internal cache for metadata decoding. No need to track deps on this.
-    pub rcache: RefCell<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,
+    pub rcache: Lock<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,
 
     /// Caches the results of trait selection. This cache is used
     /// for things that do not have to do with the parameters in scope.
@@ -857,23 +856,23 @@ pub struct GlobalCtxt<'tcx> {
     pub data_layout: TargetDataLayout,
 
     /// Used to prevent layout from recursing too deeply.
-    pub layout_depth: Cell<usize>,
+    pub layout_depth: LockCell<usize>,
 
     /// Map from function to the `#[derive]` mode that it's defining. Only used
     /// by `proc-macro` crates.
-    pub derive_macros: RefCell<NodeMap<Symbol>>,
+    pub derive_macros: Lock<NodeMap<Symbol>>,
 
-    stability_interner: RefCell<FxHashSet<&'tcx attr::Stability>>,
+    stability_interner: Lock<FxHashSet<&'tcx attr::Stability>>,
 
-    pub interpret_interner: RefCell<InterpretInterner<'tcx>>,
+    pub interpret_interner: Lock<InterpretInterner<'tcx>>,
 
-    layout_interner: RefCell<FxHashSet<&'tcx LayoutDetails>>,
+    layout_interner: Lock<FxHashSet<&'tcx LayoutDetails>>,
 
     /// A vector of every trait accessible in the whole crate
     /// (i.e. including those from subcrates). This is used only for
     /// error reporting, and so is lazily initialized and generally
-    /// shouldn't taint the common path (hence the RefCell).
-    pub all_traits: RefCell<Option<Vec<DefId>>>,
+    /// shouldn't taint the common path (hence the Lock).
+    pub all_traits: Lock<Option<Vec<DefId>>>,
 
     /// A general purpose channel to throw data out the back towards LLVM worker
     /// threads.
@@ -881,7 +880,7 @@ pub struct GlobalCtxt<'tcx> {
     /// This is intended to only get used during the trans phase of the compiler
     /// when satisfying the query for a particular codegen unit. Internally in
     /// the query it'll send data along this channel to get processed later.
-    pub tx_to_llvm_workers: mpsc::Sender<Box<Any + Send>>,
+    pub tx_to_llvm_workers: Lock<mpsc::Sender<Box<Any + Send>>>,
 
     output_filenames: Arc<OutputFilenames>,
 }
@@ -1131,7 +1130,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     /// value (types, substs, etc.) can only be used while `ty::tls` has a valid
     /// reference to the context, to allow formatting values that need it.
     pub fn create_and_enter<F, R>(s: &'tcx Session,
-                                  cstore: &'tcx CrateStore,
+                                  cstore: &'tcx (CrateStore + Sync),
                                   local_providers: ty::maps::Providers<'tcx>,
                                   extern_providers: ty::maps::Providers<'tcx>,
                                   arenas: &'tcx AllArenas<'tcx>,
@@ -1153,7 +1152,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         providers[LOCAL_CRATE] = local_providers;
 
         let def_path_hash_to_def_id = if s.opts.build_dep_graph() {
-            let upstream_def_path_tables: Vec<(CrateNum, Rc<_>)> = cstore
+            let upstream_def_path_tables: Vec<(CrateNum, Lrc<_>)> = cstore
                 .crates_untracked()
                 .iter()
                 .map(|&cnum| (cnum, cstore.def_path_table(cnum)))
@@ -1188,10 +1187,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         for (k, v) in resolutions.trait_map {
             let hir_id = hir.node_to_hir_id(k);
             let map = trait_map.entry(hir_id.owner)
-                .or_insert_with(|| Rc::new(FxHashMap()));
-            Rc::get_mut(map).unwrap()
+                .or_insert_with(|| Lrc::new(FxHashMap()));
+            Lrc::get_mut(map).unwrap()
                             .insert(hir_id.local_id,
-                                    Rc::new(StableVec::new(v)));
+                                    Lrc::new(StableVec::new(v)));
         }
 
         tls::enter_global(GlobalCtxt {
@@ -1204,10 +1203,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             types: common_types,
             trait_map,
             export_map: resolutions.export_map.into_iter().map(|(k, v)| {
-                (k, Rc::new(v))
+                (k, Lrc::new(v))
             }).collect(),
             freevars: resolutions.freevars.into_iter().map(|(k, v)| {
-                (hir.local_def_id(k), Rc::new(v))
+                (hir.local_def_id(k), Lrc::new(v))
             }).collect(),
             maybe_unused_trait_imports:
                 resolutions.maybe_unused_trait_imports
@@ -1222,18 +1221,18 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             hir,
             def_path_hash_to_def_id,
             maps: maps::Maps::new(providers),
-            rcache: RefCell::new(FxHashMap()),
+            rcache: Lock::new(FxHashMap()),
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
             crate_name: Symbol::intern(crate_name),
             data_layout,
-            layout_interner: RefCell::new(FxHashSet()),
-            layout_depth: Cell::new(0),
-            derive_macros: RefCell::new(NodeMap()),
-            stability_interner: RefCell::new(FxHashSet()),
-            interpret_interner: Default::default(),
-            all_traits: RefCell::new(None),
-            tx_to_llvm_workers: tx,
+            layout_interner: Lock::new(FxHashSet()),
+            layout_depth: LockCell::new(0),
+            derive_macros: Lock::new(NodeMap()),
+            stability_interner: Lock::new(FxHashSet()),
+            interpret_interner: Lock::new(Default::default()),
+            all_traits: Lock::new(None),
+            tx_to_llvm_workers: Lock::new(tx),
             output_filenames: Arc::new(output_filenames.clone()),
        }, f)
     }
@@ -1243,15 +1242,15 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.sess.consider_optimizing(&cname, msg)
     }
 
-    pub fn lang_items(self) -> Rc<middle::lang_items::LanguageItems> {
+    pub fn lang_items(self) -> Lrc<middle::lang_items::LanguageItems> {
         self.get_lang_items(LOCAL_CRATE)
     }
 
-    pub fn stability(self) -> Rc<stability::Index<'tcx>> {
+    pub fn stability(self) -> Lrc<stability::Index<'tcx>> {
         self.stability_index(LOCAL_CRATE)
     }
 
-    pub fn crates(self) -> Rc<Vec<CrateNum>> {
+    pub fn crates(self) -> Lrc<Vec<CrateNum>> {
         self.all_crate_nums(LOCAL_CRATE)
     }
 
@@ -1312,7 +1311,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
     // Note that this is *untracked* and should only be used within the query
     // system if the result is otherwise tracked through queries
-    pub fn crate_data_as_rc_any(self, cnum: CrateNum) -> Rc<Any> {
+    pub fn crate_data_as_rc_any(self, cnum: CrateNum) -> Lrc<Any> {
         self.cstore.crate_data_as_rc_any(cnum)
     }
 
@@ -2259,7 +2258,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         lint::struct_lint_level(self.sess, lint, level, src, None, msg)
     }
 
-    pub fn in_scope_traits(self, id: HirId) -> Option<Rc<StableVec<TraitCandidate>>> {
+    pub fn in_scope_traits(self, id: HirId) -> Option<Lrc<StableVec<TraitCandidate>>> {
         self.in_scope_traits_map(id.owner)
             .and_then(|map| map.get(&id.local_id).cloned())
     }
@@ -2276,7 +2275,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn object_lifetime_defaults(self, id: HirId)
-        -> Option<Rc<Vec<ObjectLifetimeDefault>>>
+        -> Option<Lrc<Vec<ObjectLifetimeDefault>>>
     {
         self.object_lifetime_defaults_map(id.owner)
             .and_then(|map| map.get(&id.local_id).cloned())
@@ -2347,7 +2346,7 @@ pub fn provide(providers: &mut ty::maps::Providers) {
         // Once red/green incremental compilation lands we should be able to
         // remove this because while the crate changes often the lint level map
         // will change rarely.
-        tcx.dep_graph.with_ignore(|| Rc::new(middle::lang_items::collect(tcx)))
+        tcx.dep_graph.with_ignore(|| Lrc::new(middle::lang_items::collect(tcx)))
     };
     providers.freevars = |tcx, id| tcx.gcx.freevars.get(&id).cloned();
     providers.maybe_unused_trait_import = |tcx, id| {
@@ -2355,12 +2354,12 @@ pub fn provide(providers: &mut ty::maps::Providers) {
     };
     providers.maybe_unused_extern_crates = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Rc::new(tcx.maybe_unused_extern_crates.clone())
+        Lrc::new(tcx.maybe_unused_extern_crates.clone())
     };
 
     providers.stability_index = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Rc::new(stability::Index::new(tcx))
+        Lrc::new(stability::Index::new(tcx))
     };
     providers.lookup_stability = |tcx, id| {
         assert_eq!(id.krate, LOCAL_CRATE);
@@ -2378,11 +2377,11 @@ pub fn provide(providers: &mut ty::maps::Providers) {
     };
     providers.all_crate_nums = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Rc::new(tcx.cstore.crates_untracked())
+        Lrc::new(tcx.cstore.crates_untracked())
     };
     providers.postorder_cnums = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Rc::new(tcx.cstore.postorder_cnums_untracked())
+        Lrc::new(tcx.cstore.postorder_cnums_untracked())
     };
     providers.output_filenames = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
diff --git a/src/librustc/ty/maps/mod.rs b/src/librustc/ty/maps/mod.rs
index 23531b7b942f5..27c8fadc3adb8 100644
--- a/src/librustc/ty/maps/mod.rs
+++ b/src/librustc/ty/maps/mod.rs
@@ -46,7 +46,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::StableVec;
 
 use std::ops::Deref;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::sync::Arc;
 use syntax_pos::{Span, DUMMY_SP};
 use syntax_pos::symbol::InternedString;
@@ -117,17 +117,17 @@ define_maps! { <'tcx>
 
     /// Get a map with the variance of every item; use `item_variance`
     /// instead.
-    [] fn crate_variances: crate_variances(CrateNum) -> Rc<ty::CrateVariancesMap>,
+    [] fn crate_variances: crate_variances(CrateNum) -> Lrc<ty::CrateVariancesMap>,
 
     /// Maps from def-id of a type or region parameter to its
     /// (inferred) variance.
-    [] fn variances_of: ItemVariances(DefId) -> Rc<Vec<ty::Variance>>,
+    [] fn variances_of: ItemVariances(DefId) -> Lrc<Vec<ty::Variance>>,
 
     /// Maps from def-id of a type to its (inferred) outlives.
     [] fn inferred_outlives_of: InferredOutlivesOf(DefId) -> Vec<ty::Predicate<'tcx>>,
 
     /// Maps from an impl/trait def-id to a list of the def-ids of its items
-    [] fn associated_item_def_ids: AssociatedItemDefIds(DefId) -> Rc<Vec<DefId>>,
+    [] fn associated_item_def_ids: AssociatedItemDefIds(DefId) -> Lrc<Vec<DefId>>,
 
     /// Maps from a trait item to the trait item "descriptor"
     [] fn associated_item: AssociatedItems(DefId) -> ty::AssociatedItem,
@@ -138,17 +138,17 @@ define_maps! { <'tcx>
     /// Maps a DefId of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
     /// Methods in these implementations don't need to be exported.
-    [] fn inherent_impls: InherentImpls(DefId) -> Rc<Vec<DefId>>,
+    [] fn inherent_impls: InherentImpls(DefId) -> Lrc<Vec<DefId>>,
 
     /// Set of all the def-ids in this crate that have MIR associated with
     /// them. This includes all the body owners, but also things like struct
     /// constructors.
-    [] fn mir_keys: mir_keys(CrateNum) -> Rc<DefIdSet>,
+    [] fn mir_keys: mir_keys(CrateNum) -> Lrc<DefIdSet>,
 
     /// Maps DefId's that have an associated Mir to the result
     /// of the MIR qualify_consts pass. The actual meaning of
     /// the value isn't known except to the pass itself.
-    [] fn mir_const_qualif: MirConstQualif(DefId) -> (u8, Rc<IdxSetBuf<mir::Local>>),
+    [] fn mir_const_qualif: MirConstQualif(DefId) -> (u8, Lrc<IdxSetBuf<mir::Local>>),
 
     /// Fetch the MIR for a given def-id right after it's built - this includes
     /// unreachable code.
@@ -183,13 +183,13 @@ define_maps! { <'tcx>
 
     [] fn typeck_tables_of: TypeckTables(DefId) -> &'tcx ty::TypeckTables<'tcx>,
 
-    [] fn used_trait_imports: UsedTraitImports(DefId) -> Rc<DefIdSet>,
+    [] fn used_trait_imports: UsedTraitImports(DefId) -> Lrc<DefIdSet>,
 
     [] fn has_typeck_tables: HasTypeckTables(DefId) -> bool,
 
     [] fn coherent_trait: coherent_trait_dep_node((CrateNum, DefId)) -> (),
 
-    [] fn borrowck: BorrowCheck(DefId) -> Rc<BorrowCheckResult>,
+    [] fn borrowck: BorrowCheck(DefId) -> Lrc<BorrowCheckResult>,
 
     /// Borrow checks the function body. If this is a closure, returns
     /// additional requirements that the closure's creator must verify.
@@ -214,13 +214,13 @@ define_maps! { <'tcx>
         -> Result<(), ErrorReported>,
 
     /// Performs the privacy check and computes "access levels".
-    [] fn privacy_access_levels: PrivacyAccessLevels(CrateNum) -> Rc<AccessLevels>,
+    [] fn privacy_access_levels: PrivacyAccessLevels(CrateNum) -> Lrc<AccessLevels>,
 
     [] fn reachable_set: reachability_dep_node(CrateNum) -> ReachableSet,
 
     /// Per-body `region::ScopeTree`. The `DefId` should be the owner-def-id for the body;
     /// in the case of closures, this will be redirected to the enclosing function.
-    [] fn region_scope_tree: RegionScopeTree(DefId) -> Rc<region::ScopeTree>,
+    [] fn region_scope_tree: RegionScopeTree(DefId) -> Lrc<region::ScopeTree>,
 
     [] fn mir_shims: mir_shim_dep_node(ty::InstanceDef<'tcx>) -> &'tcx mir::Mir<'tcx>,
 
@@ -231,22 +231,22 @@ define_maps! { <'tcx>
     [] fn def_span: DefSpan(DefId) -> Span,
     [] fn lookup_stability: LookupStability(DefId) -> Option<&'tcx attr::Stability>,
     [] fn lookup_deprecation_entry: LookupDeprecationEntry(DefId) -> Option<DeprecationEntry>,
-    [] fn item_attrs: ItemAttrs(DefId) -> Rc<[ast::Attribute]>,
+    [] fn item_attrs: ItemAttrs(DefId) -> Lrc<[ast::Attribute]>,
     [] fn fn_arg_names: FnArgNames(DefId) -> Vec<ast::Name>,
     [] fn impl_parent: ImplParent(DefId) -> Option<DefId>,
     [] fn trait_of_item: TraitOfItem(DefId) -> Option<DefId>,
     [] fn is_exported_symbol: IsExportedSymbol(DefId) -> bool,
     [] fn item_body_nested_bodies: ItemBodyNestedBodies(DefId) -> ExternBodyNestedBodies,
     [] fn const_is_rvalue_promotable_to_static: ConstIsRvaluePromotableToStatic(DefId) -> bool,
-    [] fn rvalue_promotable_map: RvaluePromotableMap(DefId) -> Rc<ItemLocalSet>,
+    [] fn rvalue_promotable_map: RvaluePromotableMap(DefId) -> Lrc<ItemLocalSet>,
     [] fn is_mir_available: IsMirAvailable(DefId) -> bool,
     [] fn vtable_methods: vtable_methods_node(ty::PolyTraitRef<'tcx>)
-                          -> Rc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>,
+                          -> Lrc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>,
 
     [] fn trans_fulfill_obligation: fulfill_obligation_dep_node(
         (ty::ParamEnv<'tcx>, ty::PolyTraitRef<'tcx>)) -> Vtable<'tcx, ()>,
-    [] fn trait_impls_of: TraitImpls(DefId) -> Rc<ty::trait_def::TraitImpls>,
-    [] fn specialization_graph_of: SpecializationGraph(DefId) -> Rc<specialization_graph::Graph>,
+    [] fn trait_impls_of: TraitImpls(DefId) -> Lrc<ty::trait_def::TraitImpls>,
+    [] fn specialization_graph_of: SpecializationGraph(DefId) -> Lrc<specialization_graph::Graph>,
     [] fn is_object_safe: ObjectSafety(DefId) -> bool,
 
     // Get the ParameterEnvironment for a given item; this environment
@@ -268,7 +268,7 @@ define_maps! { <'tcx>
                                             ty::layout::LayoutError<'tcx>>,
 
     [] fn dylib_dependency_formats: DylibDepFormats(CrateNum)
-                                    -> Rc<Vec<(CrateNum, LinkagePreference)>>,
+                                    -> Lrc<Vec<(CrateNum, LinkagePreference)>>,
 
     [] fn is_panic_runtime: IsPanicRuntime(CrateNum) -> bool,
     [] fn is_compiler_builtins: IsCompilerBuiltins(CrateNum) -> bool,
@@ -278,17 +278,17 @@ define_maps! { <'tcx>
     [] fn panic_strategy: GetPanicStrategy(CrateNum) -> PanicStrategy,
     [] fn is_no_builtins: IsNoBuiltins(CrateNum) -> bool,
 
-    [] fn extern_crate: ExternCrate(DefId) -> Rc<Option<ExternCrate>>,
+    [] fn extern_crate: ExternCrate(DefId) -> Lrc<Option<ExternCrate>>,
 
     [] fn specializes: specializes_node((DefId, DefId)) -> bool,
     [] fn in_scope_traits_map: InScopeTraits(DefIndex)
-        -> Option<Rc<FxHashMap<ItemLocalId, Rc<StableVec<TraitCandidate>>>>>,
-    [] fn module_exports: ModuleExports(DefId) -> Option<Rc<Vec<Export>>>,
-    [] fn lint_levels: lint_levels_node(CrateNum) -> Rc<lint::LintLevelMap>,
+        -> Option<Lrc<FxHashMap<ItemLocalId, Lrc<StableVec<TraitCandidate>>>>>,
+    [] fn module_exports: ModuleExports(DefId) -> Option<Lrc<Vec<Export>>>,
+    [] fn lint_levels: lint_levels_node(CrateNum) -> Lrc<lint::LintLevelMap>,
 
     [] fn impl_defaultness: ImplDefaultness(DefId) -> hir::Defaultness,
-    [] fn exported_symbol_ids: ExportedSymbolIds(CrateNum) -> Rc<DefIdSet>,
-    [] fn native_libraries: NativeLibraries(CrateNum) -> Rc<Vec<NativeLibrary>>,
+    [] fn exported_symbol_ids: ExportedSymbolIds(CrateNum) -> Lrc<DefIdSet>,
+    [] fn native_libraries: NativeLibraries(CrateNum) -> Lrc<Vec<NativeLibrary>>,
     [] fn plugin_registrar_fn: PluginRegistrarFn(CrateNum) -> Option<DefId>,
     [] fn derive_registrar_fn: DeriveRegistrarFn(CrateNum) -> Option<DefId>,
     [] fn crate_disambiguator: CrateDisambiguator(CrateNum) -> CrateDisambiguator,
@@ -296,48 +296,48 @@ define_maps! { <'tcx>
     [] fn original_crate_name: OriginalCrateName(CrateNum) -> Symbol,
 
     [] fn implementations_of_trait: implementations_of_trait_node((CrateNum, DefId))
-        -> Rc<Vec<DefId>>,
+        -> Lrc<Vec<DefId>>,
     [] fn all_trait_implementations: AllTraitImplementations(CrateNum)
-        -> Rc<Vec<DefId>>,
+        -> Lrc<Vec<DefId>>,
 
     [] fn is_dllimport_foreign_item: IsDllimportForeignItem(DefId) -> bool,
     [] fn is_statically_included_foreign_item: IsStaticallyIncludedForeignItem(DefId) -> bool,
     [] fn native_library_kind: NativeLibraryKind(DefId)
         -> Option<NativeLibraryKind>,
-    [] fn link_args: link_args_node(CrateNum) -> Rc<Vec<String>>,
+    [] fn link_args: link_args_node(CrateNum) -> Lrc<Vec<String>>,
 
     // Lifetime resolution. See `middle::resolve_lifetimes`.
-    [] fn resolve_lifetimes: ResolveLifetimes(CrateNum) -> Rc<ResolveLifetimes>,
+    [] fn resolve_lifetimes: ResolveLifetimes(CrateNum) -> Lrc<ResolveLifetimes>,
     [] fn named_region_map: NamedRegion(DefIndex) ->
-        Option<Rc<FxHashMap<ItemLocalId, Region>>>,
+        Option<Lrc<FxHashMap<ItemLocalId, Region>>>,
     [] fn is_late_bound_map: IsLateBound(DefIndex) ->
-        Option<Rc<FxHashSet<ItemLocalId>>>,
+        Option<Lrc<FxHashSet<ItemLocalId>>>,
     [] fn object_lifetime_defaults_map: ObjectLifetimeDefaults(DefIndex)
-        -> Option<Rc<FxHashMap<ItemLocalId, Rc<Vec<ObjectLifetimeDefault>>>>>,
+        -> Option<Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
 
     [] fn visibility: Visibility(DefId) -> ty::Visibility,
     [] fn dep_kind: DepKind(CrateNum) -> DepKind,
     [] fn crate_name: CrateName(CrateNum) -> Symbol,
-    [] fn item_children: ItemChildren(DefId) -> Rc<Vec<Export>>,
+    [] fn item_children: ItemChildren(DefId) -> Lrc<Vec<Export>>,
     [] fn extern_mod_stmt_cnum: ExternModStmtCnum(DefId) -> Option<CrateNum>,
 
-    [] fn get_lang_items: get_lang_items_node(CrateNum) -> Rc<LanguageItems>,
-    [] fn defined_lang_items: DefinedLangItems(CrateNum) -> Rc<Vec<(DefId, usize)>>,
-    [] fn missing_lang_items: MissingLangItems(CrateNum) -> Rc<Vec<LangItem>>,
+    [] fn get_lang_items: get_lang_items_node(CrateNum) -> Lrc<LanguageItems>,
+    [] fn defined_lang_items: DefinedLangItems(CrateNum) -> Lrc<Vec<(DefId, usize)>>,
+    [] fn missing_lang_items: MissingLangItems(CrateNum) -> Lrc<Vec<LangItem>>,
     [] fn extern_const_body: ExternConstBody(DefId) -> ExternConstBody<'tcx>,
     [] fn visible_parent_map: visible_parent_map_node(CrateNum)
-        -> Rc<DefIdMap<DefId>>,
+        -> Lrc<DefIdMap<DefId>>,
     [] fn missing_extern_crate_item: MissingExternCrateItem(CrateNum) -> bool,
-    [] fn used_crate_source: UsedCrateSource(CrateNum) -> Rc<CrateSource>,
-    [] fn postorder_cnums: postorder_cnums_node(CrateNum) -> Rc<Vec<CrateNum>>,
+    [] fn used_crate_source: UsedCrateSource(CrateNum) -> Lrc<CrateSource>,
+    [] fn postorder_cnums: postorder_cnums_node(CrateNum) -> Lrc<Vec<CrateNum>>,
 
-    [] fn freevars: Freevars(DefId) -> Option<Rc<Vec<hir::Freevar>>>,
+    [] fn freevars: Freevars(DefId) -> Option<Lrc<Vec<hir::Freevar>>>,
     [] fn maybe_unused_trait_import: MaybeUnusedTraitImport(DefId) -> bool,
     [] fn maybe_unused_extern_crates: maybe_unused_extern_crates_node(CrateNum)
-        -> Rc<Vec<(DefId, Span)>>,
+        -> Lrc<Vec<(DefId, Span)>>,
 
-    [] fn stability_index: stability_index_node(CrateNum) -> Rc<stability::Index<'tcx>>,
-    [] fn all_crate_nums: all_crate_nums_node(CrateNum) -> Rc<Vec<CrateNum>>,
+    [] fn stability_index: stability_index_node(CrateNum) -> Lrc<stability::Index<'tcx>>,
+    [] fn all_crate_nums: all_crate_nums_node(CrateNum) -> Lrc<Vec<CrateNum>>,
 
     [] fn exported_symbols: ExportedSymbols(CrateNum)
         -> Arc<Vec<(String, Option<DefId>, SymbolExportLevel)>>,
diff --git a/src/librustc/ty/maps/on_disk_cache.rs b/src/librustc/ty/maps/on_disk_cache.rs
index 079b518efd898..105b1703fa213 100644
--- a/src/librustc/ty/maps/on_disk_cache.rs
+++ b/src/librustc/ty/maps/on_disk_cache.rs
@@ -17,14 +17,13 @@ use hir::map::definitions::DefPathHash;
 use ich::CachingCodemapView;
 use mir;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::{Lrc, Lock};
 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder, opaque,
                       SpecializedDecoder, SpecializedEncoder,
                       UseSpecializedDecodable, UseSpecializedEncodable};
 use session::{CrateDisambiguator, Session};
-use std::cell::RefCell;
 use std::mem;
-use std::rc::Rc;
 use syntax::ast::NodeId;
 use syntax::codemap::{CodeMap, StableFilemapId};
 use syntax_pos::{BytePos, Span, DUMMY_SP, FileMap};
@@ -56,17 +55,17 @@ pub struct OnDiskCache<'sess> {
 
     // This field collects all Diagnostics emitted during the current
     // compilation session.
-    current_diagnostics: RefCell<FxHashMap<DepNodeIndex, Vec<Diagnostic>>>,
+    current_diagnostics: Lock<FxHashMap<DepNodeIndex, Vec<Diagnostic>>>,
 
     prev_cnums: Vec<(u32, String, CrateDisambiguator)>,
-    cnum_map: RefCell<Option<IndexVec<CrateNum, Option<CrateNum>>>>,
+    cnum_map: Lock<Option<IndexVec<CrateNum, Option<CrateNum>>>>,
 
     codemap: &'sess CodeMap,
     file_index_to_stable_id: FxHashMap<FileMapIndex, StableFilemapId>,
 
     // These two fields caches that are populated lazily during decoding.
-    file_index_to_file: RefCell<FxHashMap<FileMapIndex, Rc<FileMap>>>,
-    synthetic_expansion_infos: RefCell<FxHashMap<AbsoluteBytePos, SyntaxContext>>,
+    file_index_to_file: Lock<FxHashMap<FileMapIndex, Lrc<FileMap>>>,
+    synthetic_expansion_infos: Lock<FxHashMap<AbsoluteBytePos, SyntaxContext>>,
 
     // A map from dep-node to the position of the cached query result in
     // `serialized_data`.
@@ -132,14 +131,14 @@ impl<'sess> OnDiskCache<'sess> {
         OnDiskCache {
             serialized_data: data,
             file_index_to_stable_id: footer.file_index_to_stable_id,
-            file_index_to_file: RefCell::new(FxHashMap()),
+            file_index_to_file: Lock::new(FxHashMap()),
             prev_cnums: footer.prev_cnums,
-            cnum_map: RefCell::new(None),
+            cnum_map: Lock::new(None),
             codemap: sess.codemap(),
-            current_diagnostics: RefCell::new(FxHashMap()),
+            current_diagnostics: Lock::new(FxHashMap()),
             query_result_index: footer.query_result_index.into_iter().collect(),
             prev_diagnostics_index: footer.diagnostics_index.into_iter().collect(),
-            synthetic_expansion_infos: RefCell::new(FxHashMap()),
+            synthetic_expansion_infos: Lock::new(FxHashMap()),
         }
     }
 
@@ -147,14 +146,14 @@ impl<'sess> OnDiskCache<'sess> {
         OnDiskCache {
             serialized_data: Vec::new(),
             file_index_to_stable_id: FxHashMap(),
-            file_index_to_file: RefCell::new(FxHashMap()),
+            file_index_to_file: Lock::new(FxHashMap()),
             prev_cnums: vec![],
-            cnum_map: RefCell::new(None),
+            cnum_map: Lock::new(None),
             codemap,
-            current_diagnostics: RefCell::new(FxHashMap()),
+            current_diagnostics: Lock::new(FxHashMap()),
             query_result_index: FxHashMap(),
             prev_diagnostics_index: FxHashMap(),
-            synthetic_expansion_infos: RefCell::new(FxHashMap()),
+            synthetic_expansion_infos: Lock::new(FxHashMap()),
         }
     }
 
@@ -356,9 +355,9 @@ impl<'sess> OnDiskCache<'sess> {
             opaque: opaque::Decoder::new(&self.serialized_data[..], pos.to_usize()),
             codemap: self.codemap,
             cnum_map: cnum_map.as_ref().unwrap(),
-            file_index_to_file: &mut file_index_to_file,
+            file_index_to_file: &mut *file_index_to_file,
             file_index_to_stable_id: &self.file_index_to_stable_id,
-            synthetic_expansion_infos: &mut synthetic_expansion_infos,
+            synthetic_expansion_infos: &mut *synthetic_expansion_infos,
         };
 
         match decode_tagged(&mut decoder, dep_node_index) {
@@ -418,12 +417,12 @@ struct CacheDecoder<'a, 'tcx: 'a, 'x> {
     codemap: &'x CodeMap,
     cnum_map: &'x IndexVec<CrateNum, Option<CrateNum>>,
     synthetic_expansion_infos: &'x mut FxHashMap<AbsoluteBytePos, SyntaxContext>,
-    file_index_to_file: &'x mut FxHashMap<FileMapIndex, Rc<FileMap>>,
+    file_index_to_file: &'x mut FxHashMap<FileMapIndex, Lrc<FileMap>>,
     file_index_to_stable_id: &'x FxHashMap<FileMapIndex, StableFilemapId>,
 }
 
 impl<'a, 'tcx, 'x> CacheDecoder<'a, 'tcx, 'x> {
-    fn file_index_to_file(&mut self, index: FileMapIndex) -> Rc<FileMap> {
+    fn file_index_to_file(&mut self, index: FileMapIndex) -> Lrc<FileMap> {
         let CacheDecoder {
             ref mut file_index_to_file,
             ref file_index_to_stable_id,
@@ -696,7 +695,7 @@ struct CacheEncoder<'enc, 'a, 'tcx, E>
 impl<'enc, 'a, 'tcx, E> CacheEncoder<'enc, 'a, 'tcx, E>
     where E: 'enc + ty_codec::TyEncoder
 {
-    fn filemap_index(&mut self, filemap: Rc<FileMap>) -> FileMapIndex {
+    fn filemap_index(&mut self, filemap: Lrc<FileMap>) -> FileMapIndex {
         self.file_to_file_index[&(&*filemap as *const FileMap)]
     }
 
diff --git a/src/librustc/ty/maps/plumbing.rs b/src/librustc/ty/maps/plumbing.rs
index 8875439be6b3d..254c71636e535 100644
--- a/src/librustc/ty/maps/plumbing.rs
+++ b/src/librustc/ty/maps/plumbing.rs
@@ -20,7 +20,7 @@ use ty::maps::config::QueryDescription;
 use ty::item_path;
 
 use rustc_data_structures::fx::{FxHashMap};
-use std::cell::{Ref, RefMut};
+use rustc_data_structures::sync::LockGuard;
 use std::marker::PhantomData;
 use std::mem;
 use syntax_pos::Span;
@@ -57,12 +57,12 @@ impl<'tcx, M: QueryDescription<'tcx>> QueryMap<'tcx, M> {
 
 pub(super) trait GetCacheInternal<'tcx>: QueryDescription<'tcx> + Sized {
     fn get_cache_internal<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
-                              -> Ref<'a, QueryMap<'tcx, Self>>;
+                              -> LockGuard<'a, QueryMap<'tcx, Self>>;
 }
 
 pub(super) struct CycleError<'a, 'tcx: 'a> {
     span: Span,
-    cycle: RefMut<'a, [(Span, Query<'tcx>)]>,
+    cycle: LockGuard<'a, [(Span, Query<'tcx>)]>,
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
@@ -112,7 +112,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                                        .find(|&(_, &(_, ref q))| *q == query) {
                 return Err(CycleError {
                     span,
-                    cycle: RefMut::map(stack, |stack| &mut stack[i..])
+                    cycle: LockGuard::map(stack, |stack| &mut stack[i..])
                 });
             }
             stack.push((span, query));
@@ -189,7 +189,7 @@ macro_rules! define_maps {
        [$($modifiers:tt)*] fn $name:ident: $node:ident($K:ty) -> $V:ty,)*) => {
 
         use dep_graph::DepNodeIndex;
-        use std::cell::RefCell;
+        use rustc_data_structures::sync::{Lock, LockGuard};
 
         define_map_struct! {
             tcx: $tcx,
@@ -201,8 +201,8 @@ macro_rules! define_maps {
                        -> Self {
                 Maps {
                     providers,
-                    query_stack: RefCell::new(vec![]),
-                    $($name: RefCell::new(QueryMap::new())),*
+                    query_stack: Lock::new(vec![]),
+                    $($name: Lock::new(QueryMap::new())),*
                 }
             }
         }
@@ -250,7 +250,7 @@ macro_rules! define_maps {
 
         impl<$tcx> GetCacheInternal<$tcx> for queries::$name<$tcx> {
             fn get_cache_internal<'a>(tcx: TyCtxt<'a, $tcx, $tcx>)
-                                      -> ::std::cell::Ref<'a, QueryMap<$tcx, Self>> {
+                                      -> LockGuard<'a, QueryMap<$tcx, Self>> {
                 tcx.maps.$name.borrow()
             }
         }
@@ -586,8 +586,8 @@ macro_rules! define_map_struct {
      input: ($(([$(modifiers:tt)*] [$($attr:tt)*] [$name:ident]))*)) => {
         pub struct Maps<$tcx> {
             providers: IndexVec<CrateNum, Providers<$tcx>>,
-            query_stack: RefCell<Vec<(Span, Query<$tcx>)>>,
-            $($(#[$attr])*  $name: RefCell<QueryMap<$tcx, queries::$name<$tcx>>>,)*
+            query_stack: Lock<Vec<(Span, Query<$tcx>)>>,
+            $($(#[$attr])*  $name: Lock<QueryMap<$tcx, queries::$name<$tcx>>>,)*
         }
     };
 }
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index e03e1237466e6..e6ad5084b5022 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -42,7 +42,7 @@ use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::iter::FromIterator;
 use std::ops::Deref;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::slice;
 use std::vec::IntoIter;
 use std::mem;
@@ -124,7 +124,7 @@ mod sty;
 /// *on-demand* infrastructure.
 #[derive(Clone)]
 pub struct CrateAnalysis {
-    pub access_levels: Rc<AccessLevels>,
+    pub access_levels: Lrc<AccessLevels>,
     pub name: String,
     pub glob_map: Option<hir::GlobMap>,
 }
@@ -336,10 +336,10 @@ pub struct CrateVariancesMap {
     /// For each item with generics, maps to a vector of the variance
     /// of its generics.  If an item has no generics, it will have no
     /// entry.
-    pub variances: FxHashMap<DefId, Rc<Vec<ty::Variance>>>,
+    pub variances: FxHashMap<DefId, Lrc<Vec<ty::Variance>>>,
 
     /// An empty vector, useful for cloning.
-    pub empty_variance: Rc<Vec<ty::Variance>>,
+    pub empty_variance: Lrc<Vec<ty::Variance>>,
 }
 
 impl Variance {
@@ -2102,7 +2102,7 @@ impl BorrowKind {
 
 #[derive(Debug, Clone)]
 pub enum Attributes<'gcx> {
-    Owned(Rc<[ast::Attribute]>),
+    Owned(Lrc<[ast::Attribute]>),
     Borrowed(&'gcx [ast::Attribute])
 }
 
@@ -2587,7 +2587,7 @@ fn adt_dtorck_constraint<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn associated_item_def_ids<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                      def_id: DefId)
-                                     -> Rc<Vec<DefId>> {
+                                     -> Lrc<Vec<DefId>> {
     let id = tcx.hir.as_local_node_id(def_id).unwrap();
     let item = tcx.hir.expect_item(id);
     let vec: Vec<_> = match item.node {
@@ -2606,7 +2606,7 @@ fn associated_item_def_ids<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         hir::ItemTraitAlias(..) => vec![],
         _ => span_bug!(item.span, "associated_item_def_ids: not impl or trait")
     };
-    Rc::new(vec)
+    Lrc::new(vec)
 }
 
 fn def_span<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Span {
@@ -2696,7 +2696,7 @@ pub fn provide(providers: &mut ty::maps::Providers) {
 /// (constructing this map requires touching the entire crate).
 #[derive(Clone, Debug)]
 pub struct CrateInherentImpls {
-    pub inherent_impls: DefIdMap<Rc<Vec<DefId>>>,
+    pub inherent_impls: DefIdMap<Lrc<Vec<DefId>>>,
 }
 
 /// A set of constraints that need to be satisfied in order for
diff --git a/src/librustc/ty/steal.rs b/src/librustc/ty/steal.rs
index 0b0818888812f..08f48dfb6d924 100644
--- a/src/librustc/ty/steal.rs
+++ b/src/librustc/ty/steal.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::cell::{Ref, RefCell};
+use rustc_data_structures::sync::{RwLock, ReadGuard};
 use std::mem;
 
 /// The `Steal` struct is intended to used as the value for a query.
@@ -32,18 +32,18 @@ use std::mem;
 ///
 /// FIXME(#41710) -- what is the best way to model linear queries?
 pub struct Steal<T> {
-    value: RefCell<Option<T>>
+    value: RwLock<Option<T>>
 }
 
 impl<T> Steal<T> {
     pub fn new(value: T) -> Self {
         Steal {
-            value: RefCell::new(Some(value))
+            value: RwLock::new(Some(value))
         }
     }
 
-    pub fn borrow(&self) -> Ref<T> {
-        Ref::map(self.value.borrow(), |opt| match *opt {
+    pub fn borrow(&self) -> ReadGuard<T> {
+        ReadGuard::map(self.value.borrow(), |opt| match *opt {
             None => bug!("attempted to read from stolen value"),
             Some(ref v) => v
         })
diff --git a/src/librustc/ty/trait_def.rs b/src/librustc/ty/trait_def.rs
index 0fbf9f1bd587b..62d3c8dc87da3 100644
--- a/src/librustc/ty/trait_def.rs
+++ b/src/librustc/ty/trait_def.rs
@@ -20,7 +20,7 @@ use ty::{Ty, TyCtxt};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
                                            StableHasherResult};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 /// A trait's definition with type information.
 pub struct TraitDef {
@@ -142,7 +142,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 // Query provider for `trait_impls_of`.
 pub(super) fn trait_impls_of_provider<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                 trait_id: DefId)
-                                                -> Rc<TraitImpls> {
+                                                -> Lrc<TraitImpls> {
     let mut remote_impls = Vec::new();
 
     // Traits defined in the current crate can't have impls in upstream
@@ -180,7 +180,7 @@ pub(super) fn trait_impls_of_provider<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         }
     }
 
-    Rc::new(TraitImpls {
+    Lrc::new(TraitImpls {
         blanket_impls: blanket_impls,
         non_blanket_impls: non_blanket_impls,
     })
diff --git a/src/librustc/util/common.rs b/src/librustc/util/common.rs
index 76d3494dbf082..51a9034ec3f8c 100644
--- a/src/librustc/util/common.rs
+++ b/src/librustc/util/common.rs
@@ -10,6 +10,8 @@
 
 #![allow(non_camel_case_types)]
 
+use rustc_data_structures::sync::LockCell;
+
 use std::cell::{RefCell, Cell};
 use std::collections::HashMap;
 use std::ffi::CString;
@@ -205,7 +207,7 @@ pub fn to_readable_str(mut val: usize) -> String {
     groups.join("_")
 }
 
-pub fn record_time<T, F>(accu: &Cell<Duration>, f: F) -> T where
+pub fn record_time<T, F>(accu: &LockCell<Duration>, f: F) -> T where
     F: FnOnce() -> T,
 {
     let start = Instant::now();
diff --git a/src/librustc_borrowck/Cargo.toml b/src/librustc_borrowck/Cargo.toml
index 25f02537490fa..abc1fc759f696 100644
--- a/src/librustc_borrowck/Cargo.toml
+++ b/src/librustc_borrowck/Cargo.toml
@@ -17,3 +17,4 @@ graphviz = { path = "../libgraphviz" }
 rustc = { path = "../librustc" }
 rustc_mir = { path = "../librustc_mir" }
 rustc_errors = { path = "../librustc_errors" }
+rustc_data_structures = { path = "../librustc_data_structures" }
\ No newline at end of file
diff --git a/src/librustc_borrowck/borrowck/mod.rs b/src/librustc_borrowck/borrowck/mod.rs
index b124872ba12ca..f206cf0e3155d 100644
--- a/src/librustc_borrowck/borrowck/mod.rs
+++ b/src/librustc_borrowck/borrowck/mod.rs
@@ -44,6 +44,7 @@ use rustc::util::nodemap::FxHashSet;
 use std::cell::RefCell;
 use std::fmt;
 use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::hash::{Hash, Hasher};
 use syntax::ast;
 use syntax_pos::{MultiSpan, Span};
@@ -86,7 +87,7 @@ pub struct AnalysisData<'a, 'tcx: 'a> {
 }
 
 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
-    -> Rc<BorrowCheckResult>
+    -> Lrc<BorrowCheckResult>
 {
     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
 
@@ -99,7 +100,7 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
             // those things (notably the synthesized constructors from
             // tuple structs/variants) do not have an associated body
             // and do not need borrowchecking.
-            return Rc::new(BorrowCheckResult {
+            return Lrc::new(BorrowCheckResult {
                 used_mut_nodes: FxHashSet(),
             })
         }
@@ -127,7 +128,7 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
     // Note that `mir_validated` is a "stealable" result; the
     // thief, `optimized_mir()`, forces borrowck, so we know that
     // is not yet stolen.
-    tcx.mir_validated(owner_def_id).borrow();
+    let _guard = tcx.mir_validated(owner_def_id).borrow();
 
     // option dance because you can't capture an uninitialized variable
     // by mut-ref.
@@ -145,7 +146,7 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
     }
     unused::check(&mut bccx, body);
 
-    Rc::new(BorrowCheckResult {
+    Lrc::new(BorrowCheckResult {
         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
     })
 }
@@ -243,7 +244,7 @@ pub struct BorrowckCtxt<'a, 'tcx: 'a> {
     // Some in `borrowck_fn` and cleared later
     tables: &'a ty::TypeckTables<'tcx>,
 
-    region_scope_tree: Rc<region::ScopeTree>,
+    region_scope_tree: Lrc<region::ScopeTree>,
 
     owner_def_id: DefId,
 
diff --git a/src/librustc_borrowck/lib.rs b/src/librustc_borrowck/lib.rs
index be173db23a52a..2bdee3198f22a 100644
--- a/src/librustc_borrowck/lib.rs
+++ b/src/librustc_borrowck/lib.rs
@@ -23,6 +23,7 @@
 extern crate syntax;
 extern crate syntax_pos;
 extern crate rustc_errors as errors;
+extern crate rustc_data_structures;
 
 // for "clarity", rename the graphviz crate to dot; graphviz within `borrowck`
 // refers to the borrowck-specific graphviz adapter traits.
diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs
index c0bbab35e1e95..18fd4062c825e 100644
--- a/src/librustc_driver/driver.rs
+++ b/src/librustc_driver/driver.rs
@@ -51,7 +51,7 @@ use std::fs;
 use std::io::{self, Write};
 use std::iter;
 use std::path::{Path, PathBuf};
-use std::rc::Rc;
+use rustc_data_structures::sync::{Sync, Lrc};
 use std::sync::mpsc;
 use syntax::{ast, diagnostics, visit};
 use syntax::attr;
@@ -919,7 +919,7 @@ pub fn phase_2_configure_and_expand<F>(sess: &Session,
         expanded_crate: krate,
         defs: resolver.definitions,
         analysis: ty::CrateAnalysis {
-            access_levels: Rc::new(AccessLevels::default()),
+            access_levels: Lrc::new(AccessLevels::default()),
             name: crate_name.to_string(),
             glob_map: if resolver.make_glob_map { Some(resolver.glob_map) } else { None },
         },
@@ -962,7 +962,7 @@ pub fn default_provide_extern(providers: &mut ty::maps::Providers) {
 /// structures carrying the results of the analysis.
 pub fn phase_3_run_analysis_passes<'tcx, F, R>(control: &CompileController,
                                                sess: &'tcx Session,
-                                               cstore: &'tcx CrateStore,
+                                               cstore: &'tcx (CrateStore + Sync),
                                                hir_map: hir_map::Map<'tcx>,
                                                mut analysis: ty::CrateAnalysis,
                                                resolutions: Resolutions,
diff --git a/src/librustc_driver/lib.rs b/src/librustc_driver/lib.rs
index 5fa823659287a..e5b4d47c49c4d 100644
--- a/src/librustc_driver/lib.rs
+++ b/src/librustc_driver/lib.rs
@@ -25,6 +25,8 @@
 #![feature(rustc_diagnostic_macros)]
 #![feature(set_stdio)]
 
+#![recursion_limit="256"]
+
 extern crate arena;
 extern crate getopts;
 extern crate graphviz;
@@ -89,9 +91,9 @@ use std::io::{self, Read, Write};
 use std::iter::repeat;
 use std::path::PathBuf;
 use std::process::{self, Command, Stdio};
-use std::rc::Rc;
 use std::str;
 use std::sync::{Arc, Mutex};
+use rustc_data_structures::sync::Lrc;
 use std::thread;
 
 use syntax::ast;
@@ -187,7 +189,7 @@ mod rustc_trans {
 // The FileLoader provides a way to load files from sources other than the file system.
 pub fn run_compiler<'a>(args: &[String],
                         callbacks: &mut CompilerCalls<'a>,
-                        file_loader: Option<Box<FileLoader + 'static>>,
+                        file_loader: Option<Box<FileLoader + Send + Sync + 'static>>,
                         emitter_dest: Option<Box<Write + Send>>)
                         -> (CompileResult, Option<Session>)
 {
@@ -230,7 +232,7 @@ pub fn run_compiler<'a>(args: &[String],
     let cstore = CStore::new(DefaultTransCrate::metadata_loader());
 
     let loader = file_loader.unwrap_or(box RealFileLoader);
-    let codemap = Rc::new(CodeMap::with_file_loader(loader, sopts.file_path_mapping()));
+    let codemap = Lrc::new(CodeMap::with_file_loader(loader, sopts.file_path_mapping()));
     let mut sess = session::build_session_with_codemap(
         sopts, input_file_path.clone(), descriptions, codemap, emitter_dest,
     );
diff --git a/src/librustc_driver/pretty.rs b/src/librustc_driver/pretty.rs
index 76923be65cfd7..fd25add0e98b0 100644
--- a/src/librustc_driver/pretty.rs
+++ b/src/librustc_driver/pretty.rs
@@ -17,6 +17,7 @@ use self::NodesMatchingUII::*;
 
 use {abort_on_err, driver};
 
+use rustc_data_structures::sync::Sync;
 use rustc::ty::{self, TyCtxt, Resolutions, AllArenas};
 use rustc::cfg;
 use rustc::cfg::graphviz::LabelledCFG;
@@ -199,7 +200,7 @@ impl PpSourceMode {
     }
     fn call_with_pp_support_hir<'tcx, A, F>(&self,
                                                sess: &'tcx Session,
-                                               cstore: &'tcx CrateStore,
+                                               cstore: &'tcx (CrateStore + Sync),
                                                hir_map: &hir_map::Map<'tcx>,
                                                analysis: &ty::CrateAnalysis,
                                                resolutions: &Resolutions,
@@ -902,7 +903,7 @@ pub fn print_after_parsing(sess: &Session,
 }
 
 pub fn print_after_hir_lowering<'tcx, 'a: 'tcx>(sess: &'a Session,
-                                                cstore: &'tcx CrateStore,
+                                                cstore: &'tcx (CrateStore + Sync),
                                                 hir_map: &hir_map::Map<'tcx>,
                                                 analysis: &ty::CrateAnalysis,
                                                 resolutions: &Resolutions,
@@ -1058,7 +1059,7 @@ pub fn print_after_hir_lowering<'tcx, 'a: 'tcx>(sess: &'a Session,
 // with a different callback than the standard driver, so that isn't easy.
 // Instead, we call that function ourselves.
 fn print_with_analysis<'tcx, 'a: 'tcx>(sess: &'a Session,
-                                       cstore: &'a CrateStore,
+                                       cstore: &'a (CrateStore + Sync),
                                        hir_map: &hir_map::Map<'tcx>,
                                        analysis: &ty::CrateAnalysis,
                                        resolutions: &Resolutions,
diff --git a/src/librustc_driver/test.rs b/src/librustc_driver/test.rs
index 6765ea5e67a60..1421270395750 100644
--- a/src/librustc_driver/test.rs
+++ b/src/librustc_driver/test.rs
@@ -31,6 +31,7 @@ use rustc::session::{self, config};
 use rustc::session::config::{OutputFilenames, OutputTypes};
 use rustc_trans_utils::trans_crate::TransCrate;
 use std::rc::Rc;
+use rustc_data_structures::sync::{Send, Lrc};
 use syntax::ast;
 use syntax::abi::Abi;
 use syntax::codemap::{CodeMap, FilePathMapping, FileName};
@@ -108,7 +109,7 @@ fn test_env<F>(source_string: &str,
     let sess = session::build_session_(options,
                                        None,
                                        diagnostic_handler,
-                                       Rc::new(CodeMap::new(FilePathMapping::empty())));
+                                       Lrc::new(CodeMap::new(FilePathMapping::empty())));
     rustc_trans::init(&sess);
     rustc_lint::register_builtins(&mut sess.lint_store.borrow_mut(), Some(&sess));
     let input = config::Input::Str {
diff --git a/src/librustc_errors/emitter.rs b/src/librustc_errors/emitter.rs
index af556c576c035..59143651865b0 100644
--- a/src/librustc_errors/emitter.rs
+++ b/src/librustc_errors/emitter.rs
@@ -12,14 +12,14 @@ use self::Destination::*;
 
 use syntax_pos::{DUMMY_SP, FileMap, Span, MultiSpan};
 
-use {Level, CodeSuggestion, DiagnosticBuilder, SubDiagnostic, CodeMapper, DiagnosticId};
+use {Level, CodeSuggestion, DiagnosticBuilder, SubDiagnostic, CodeMapperDyn, DiagnosticId};
 use snippet::{Annotation, AnnotationType, Line, MultilineAnnotation, StyledString, Style};
 use styled_buffer::StyledBuffer;
 
+use rustc_data_structures::sync::Lrc;
 use std::borrow::Cow;
 use std::io::prelude::*;
 use std::io;
-use std::rc::Rc;
 use term;
 use std::collections::HashMap;
 use std::cmp::min;
@@ -104,19 +104,19 @@ impl ColorConfig {
 
 pub struct EmitterWriter {
     dst: Destination,
-    cm: Option<Rc<CodeMapper>>,
+    cm: Option<Lrc<CodeMapperDyn>>,
     short_message: bool,
 }
 
 struct FileWithAnnotatedLines {
-    file: Rc<FileMap>,
+    file: Lrc<FileMap>,
     lines: Vec<Line>,
     multiline_depth: usize,
 }
 
 impl EmitterWriter {
     pub fn stderr(color_config: ColorConfig,
-                  code_map: Option<Rc<CodeMapper>>,
+                  code_map: Option<Lrc<CodeMapperDyn>>,
                   short_message: bool)
                   -> EmitterWriter {
         if color_config.use_color() {
@@ -136,7 +136,7 @@ impl EmitterWriter {
     }
 
     pub fn new(dst: Box<Write + Send>,
-               code_map: Option<Rc<CodeMapper>>,
+               code_map: Option<Lrc<CodeMapperDyn>>,
                short_message: bool)
                -> EmitterWriter {
         EmitterWriter {
@@ -148,7 +148,7 @@ impl EmitterWriter {
 
     fn preprocess_annotations(&mut self, msp: &MultiSpan) -> Vec<FileWithAnnotatedLines> {
         fn add_annotation_to_file(file_vec: &mut Vec<FileWithAnnotatedLines>,
-                                  file: Rc<FileMap>,
+                                  file: Lrc<FileMap>,
                                   line_index: usize,
                                   ann: Annotation) {
 
@@ -280,7 +280,7 @@ impl EmitterWriter {
 
     fn render_source_line(&self,
                           buffer: &mut StyledBuffer,
-                          file: Rc<FileMap>,
+                          file: Lrc<FileMap>,
                           line: &Line,
                           width_offset: usize,
                           code_offset: usize) -> Vec<(usize, Style)> {
@@ -1133,8 +1133,6 @@ impl EmitterWriter {
                                level: &Level,
                                max_line_num_len: usize)
                                -> io::Result<()> {
-        use std::borrow::Borrow;
-
         if let Some(ref cm) = self.cm {
             let mut buffer = StyledBuffer::new();
 
@@ -1148,7 +1146,7 @@ impl EmitterWriter {
                                Some(Style::HeaderMsg));
 
             // Render the replacements for each suggestion
-            let suggestions = suggestion.splice_lines(cm.borrow());
+            let suggestions = suggestion.splice_lines(&**cm);
 
             let mut row_num = 2;
             for &(ref complete, ref parts) in suggestions.iter().take(MAX_SUGGESTIONS) {
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index 2ac49958d3c53..ffe9a237ec1d0 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -34,13 +34,12 @@ use self::Level::*;
 
 use emitter::{Emitter, EmitterWriter};
 
+use rustc_data_structures::sync::{Lrc, Lock, LockCell, Send, Sync};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::stable_hasher::StableHasher;
 
 use std::borrow::Cow;
-use std::cell::{RefCell, Cell};
 use std::mem;
-use std::rc::Rc;
 use std::{error, fmt};
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering::SeqCst;
@@ -95,6 +94,8 @@ pub struct SubstitutionPart {
     pub snippet: String,
 }
 
+pub type CodeMapperDyn = CodeMapper + Send + Sync;
+
 pub trait CodeMapper {
     fn lookup_char_pos(&self, pos: BytePos) -> Loc;
     fn span_to_lines(&self, sp: Span) -> FileLinesResult;
@@ -102,12 +103,13 @@ pub trait CodeMapper {
     fn span_to_filename(&self, sp: Span) -> FileName;
     fn merge_spans(&self, sp_lhs: Span, sp_rhs: Span) -> Option<Span>;
     fn call_span_if_macro(&self, sp: Span) -> Span;
-    fn ensure_filemap_source_present(&self, file_map: Rc<FileMap>) -> bool;
+    fn ensure_filemap_source_present(&self, file_map: Lrc<FileMap>) -> bool;
 }
 
 impl CodeSuggestion {
     /// Returns the assembled code suggestions and whether they should be shown with an underline.
-    pub fn splice_lines(&self, cm: &CodeMapper) -> Vec<(String, Vec<SubstitutionPart>)> {
+    pub fn splice_lines(&self, cm: &CodeMapperDyn)
+                        -> Vec<(String, Vec<SubstitutionPart>)> {
         use syntax_pos::{CharPos, Loc, Pos};
 
         fn push_trailing(buf: &mut String,
@@ -239,15 +241,15 @@ pub struct Handler {
     pub flags: HandlerFlags,
 
     err_count: AtomicUsize,
-    emitter: RefCell<Box<Emitter>>,
-    continue_after_error: Cell<bool>,
-    delayed_span_bug: RefCell<Option<Diagnostic>>,
-    tracked_diagnostics: RefCell<Option<Vec<Diagnostic>>>,
+    emitter: Lock<Box<Emitter + Send>>,
+    continue_after_error: LockCell<bool>,
+    delayed_span_bug: Lock<Option<Diagnostic>>,
+    tracked_diagnostics: Lock<Option<Vec<Diagnostic>>>,
 
     // This set contains a hash of every diagnostic that has been emitted by
     // this handler. These hashes is used to avoid emitting the same error
     // twice.
-    emitted_diagnostics: RefCell<FxHashSet<u128>>,
+    emitted_diagnostics: Lock<FxHashSet<u128>>,
 }
 
 #[derive(Default)]
@@ -261,7 +263,7 @@ impl Handler {
     pub fn with_tty_emitter(color_config: ColorConfig,
                             can_emit_warnings: bool,
                             treat_err_as_bug: bool,
-                            cm: Option<Rc<CodeMapper>>)
+                            cm: Option<Lrc<CodeMapperDyn>>)
                             -> Handler {
         Handler::with_tty_emitter_and_flags(
             color_config,
@@ -274,7 +276,7 @@ impl Handler {
     }
 
     pub fn with_tty_emitter_and_flags(color_config: ColorConfig,
-                                      cm: Option<Rc<CodeMapper>>,
+                                      cm: Option<Lrc<CodeMapperDyn>>,
                                       flags: HandlerFlags)
                                       -> Handler {
         let emitter = Box::new(EmitterWriter::stderr(color_config, cm, false));
@@ -283,7 +285,7 @@ impl Handler {
 
     pub fn with_emitter(can_emit_warnings: bool,
                         treat_err_as_bug: bool,
-                        e: Box<Emitter>)
+                        e: Box<Emitter + Send>)
                         -> Handler {
         Handler::with_emitter_and_flags(
             e,
@@ -294,15 +296,15 @@ impl Handler {
             })
     }
 
-    pub fn with_emitter_and_flags(e: Box<Emitter>, flags: HandlerFlags) -> Handler {
+    pub fn with_emitter_and_flags(e: Box<Emitter + Send>, flags: HandlerFlags) -> Handler {
         Handler {
             flags,
             err_count: AtomicUsize::new(0),
-            emitter: RefCell::new(e),
-            continue_after_error: Cell::new(true),
-            delayed_span_bug: RefCell::new(None),
-            tracked_diagnostics: RefCell::new(None),
-            emitted_diagnostics: RefCell::new(FxHashSet()),
+            emitter: Lock::new(e),
+            continue_after_error: LockCell::new(true),
+            delayed_span_bug: Lock::new(None),
+            tracked_diagnostics: Lock::new(None),
+            emitted_diagnostics: Lock::new(FxHashSet()),
         }
     }
 
diff --git a/src/librustc_metadata/creader.rs b/src/librustc_metadata/creader.rs
index 58453066cf34b..0265bb8962be0 100644
--- a/src/librustc_metadata/creader.rs
+++ b/src/librustc_metadata/creader.rs
@@ -14,6 +14,7 @@ use cstore::{self, CStore, CrateSource, MetadataBlob};
 use locator::{self, CratePaths};
 use native_libs::relevant_lib;
 use schema::CrateRoot;
+use rustc_data_structures::sync::{Lrc, RwLock, Lock, LockCell};
 
 use rustc::hir::def_id::{CrateNum, DefIndex, CRATE_DEF_INDEX};
 use rustc::hir::svh::Svh;
@@ -29,10 +30,8 @@ use rustc::util::common::record_time;
 use rustc::util::nodemap::FxHashSet;
 use rustc::hir::map::Definitions;
 
-use std::cell::{RefCell, Cell};
 use std::ops::Deref;
 use std::path::PathBuf;
-use std::rc::Rc;
 use std::{cmp, fs};
 
 use syntax::ast;
@@ -79,7 +78,7 @@ struct ExtensionCrate {
 }
 
 enum PMDSource {
-    Registered(Rc<cstore::CrateMetadata>),
+    Registered(Lrc<cstore::CrateMetadata>),
     Owned(Library),
 }
 
@@ -194,7 +193,7 @@ impl<'a> CrateLoader<'a> {
                       span: Span,
                       lib: Library,
                       dep_kind: DepKind)
-                      -> (CrateNum, Rc<cstore::CrateMetadata>) {
+                      -> (CrateNum, Lrc<cstore::CrateMetadata>) {
         info!("register crate `extern crate {} as {}`", name, ident);
         let crate_root = lib.metadata.get_root();
         self.verify_no_symbol_conflicts(span, &crate_root);
@@ -236,8 +235,8 @@ impl<'a> CrateLoader<'a> {
 
         let mut cmeta = cstore::CrateMetadata {
             name,
-            extern_crate: Cell::new(None),
-            def_path_table: Rc::new(def_path_table),
+            extern_crate: LockCell::new(None),
+            def_path_table: Lrc::new(def_path_table),
             exported_symbols,
             trait_impls,
             proc_macros: crate_root.macro_derive_registrar.map(|_| {
@@ -245,11 +244,11 @@ impl<'a> CrateLoader<'a> {
             }),
             root: crate_root,
             blob: metadata,
-            cnum_map: RefCell::new(cnum_map),
+            cnum_map: Lock::new(cnum_map),
             cnum,
-            codemap_import_info: RefCell::new(vec![]),
-            attribute_cache: RefCell::new([Vec::new(), Vec::new()]),
-            dep_kind: Cell::new(dep_kind),
+            codemap_import_info: RwLock::new(vec![]),
+            attribute_cache: Lock::new([Vec::new(), Vec::new()]),
+            dep_kind: LockCell::new(dep_kind),
             source: cstore::CrateSource {
                 dylib,
                 rlib,
@@ -274,7 +273,7 @@ impl<'a> CrateLoader<'a> {
 
         cmeta.dllimport_foreign_items = dllimports;
 
-        let cmeta = Rc::new(cmeta);
+        let cmeta = Lrc::new(cmeta);
         self.cstore.set_crate_data(cnum, cmeta.clone());
         (cnum, cmeta)
     }
@@ -287,7 +286,7 @@ impl<'a> CrateLoader<'a> {
                      span: Span,
                      path_kind: PathKind,
                      mut dep_kind: DepKind)
-                     -> (CrateNum, Rc<cstore::CrateMetadata>) {
+                     -> (CrateNum, Lrc<cstore::CrateMetadata>) {
         info!("resolving crate `extern crate {} as {}`", name, ident);
         let result = if let Some(cnum) = self.existing_match(name, hash, path_kind) {
             LoadResult::Previous(cnum)
@@ -513,7 +512,7 @@ impl<'a> CrateLoader<'a> {
     /// custom derive (and other macro-1.1 style features) are implemented via
     /// executables and custom IPC.
     fn load_derive_macros(&mut self, root: &CrateRoot, dylib: Option<PathBuf>, span: Span)
-                          -> Vec<(ast::Name, Rc<SyntaxExtension>)> {
+                          -> Vec<(ast::Name, Lrc<SyntaxExtension>)> {
         use std::{env, mem};
         use proc_macro::TokenStream;
         use proc_macro::__internal::Registry;
@@ -542,7 +541,7 @@ impl<'a> CrateLoader<'a> {
             mem::transmute::<*mut u8, fn(&mut Registry)>(sym)
         };
 
-        struct MyRegistrar(Vec<(ast::Name, Rc<SyntaxExtension>)>);
+        struct MyRegistrar(Vec<(ast::Name, Lrc<SyntaxExtension>)>);
 
         impl Registry for MyRegistrar {
             fn register_custom_derive(&mut self,
@@ -552,7 +551,7 @@ impl<'a> CrateLoader<'a> {
                 let attrs = attributes.iter().cloned().map(Symbol::intern).collect::<Vec<_>>();
                 let derive = ProcMacroDerive::new(expand, attrs.clone());
                 let derive = SyntaxExtension::ProcMacroDerive(Box::new(derive), attrs);
-                self.0.push((Symbol::intern(trait_name), Rc::new(derive)));
+                self.0.push((Symbol::intern(trait_name), Lrc::new(derive)));
             }
 
             fn register_attr_proc_macro(&mut self,
@@ -561,7 +560,7 @@ impl<'a> CrateLoader<'a> {
                 let expand = SyntaxExtension::AttrProcMacro(
                     Box::new(AttrProcMacro { inner: expand })
                 );
-                self.0.push((Symbol::intern(name), Rc::new(expand)));
+                self.0.push((Symbol::intern(name), Lrc::new(expand)));
             }
 
             fn register_bang_proc_macro(&mut self,
@@ -570,7 +569,7 @@ impl<'a> CrateLoader<'a> {
                 let expand = SyntaxExtension::ProcMacro(
                     Box::new(BangProcMacro { inner: expand })
                 );
-                self.0.push((Symbol::intern(name), Rc::new(expand)));
+                self.0.push((Symbol::intern(name), Lrc::new(expand)));
             }
         }
 
diff --git a/src/librustc_metadata/cstore.rs b/src/librustc_metadata/cstore.rs
index 87e41cae60d66..8132f8cf6212c 100644
--- a/src/librustc_metadata/cstore.rs
+++ b/src/librustc_metadata/cstore.rs
@@ -22,9 +22,7 @@ use rustc_back::PanicStrategy;
 use rustc_data_structures::indexed_vec::IndexVec;
 use rustc::util::nodemap::{FxHashMap, FxHashSet, NodeMap};
 
-use std::cell::{RefCell, Cell};
-use std::rc::Rc;
-use rustc_data_structures::owning_ref::ErasedBoxRef;
+use rustc_data_structures::sync::{Sync, Lrc, RwLock, Lock, LockCell};
 use syntax::{ast, attr};
 use syntax::ext::base::SyntaxExtension;
 use syntax::symbol::Symbol;
@@ -42,7 +40,9 @@ pub use cstore_impl::{provide, provide_extern};
 // own crate numbers.
 pub type CrateNumMap = IndexVec<CrateNum, CrateNum>;
 
-pub struct MetadataBlob(pub ErasedBoxRef<[u8]>);
+pub use rustc_data_structures::sync::MetadataRef;
+
+pub struct MetadataBlob(pub MetadataRef);
 
 /// Holds information about a syntax_pos::FileMap imported from another crate.
 /// See `imported_filemaps()` for more information.
@@ -52,7 +52,7 @@ pub struct ImportedFileMap {
     /// The end of this FileMap within the codemap of its original crate
     pub original_end_pos: syntax_pos::BytePos,
     /// The imported FileMap's representation within the local codemap
-    pub translated_filemap: Rc<syntax_pos::FileMap>,
+    pub translated_filemap: Lrc<syntax_pos::FileMap>,
 }
 
 pub struct CrateMetadata {
@@ -61,13 +61,13 @@ pub struct CrateMetadata {
     /// Information about the extern crate that caused this crate to
     /// be loaded. If this is `None`, then the crate was injected
     /// (e.g., by the allocator)
-    pub extern_crate: Cell<Option<ExternCrate>>,
+    pub extern_crate: LockCell<Option<ExternCrate>>,
 
     pub blob: MetadataBlob,
-    pub cnum_map: RefCell<CrateNumMap>,
+    pub cnum_map: Lock<CrateNumMap>,
     pub cnum: CrateNum,
-    pub codemap_import_info: RefCell<Vec<ImportedFileMap>>,
-    pub attribute_cache: RefCell<[Vec<Option<Rc<[ast::Attribute]>>>; 2]>,
+    pub codemap_import_info: RwLock<Vec<ImportedFileMap>>,
+    pub attribute_cache: Lock<[Vec<Option<Lrc<[ast::Attribute]>>>; 2]>,
 
     pub root: schema::CrateRoot,
 
@@ -76,32 +76,32 @@ pub struct CrateMetadata {
     /// hashmap, which gives the reverse mapping.  This allows us to
     /// quickly retrace a `DefPath`, which is needed for incremental
     /// compilation support.
-    pub def_path_table: Rc<DefPathTable>,
+    pub def_path_table: Lrc<DefPathTable>,
 
     pub exported_symbols: FxHashSet<DefIndex>,
 
     pub trait_impls: FxHashMap<(u32, DefIndex), schema::LazySeq<DefIndex>>,
 
-    pub dep_kind: Cell<DepKind>,
+    pub dep_kind: LockCell<DepKind>,
     pub source: CrateSource,
 
-    pub proc_macros: Option<Vec<(ast::Name, Rc<SyntaxExtension>)>>,
+    pub proc_macros: Option<Vec<(ast::Name, Lrc<SyntaxExtension>)>>,
     // Foreign items imported from a dylib (Windows only)
     pub dllimport_foreign_items: FxHashSet<DefIndex>,
 }
 
 pub struct CStore {
-    metas: RefCell<FxHashMap<CrateNum, Rc<CrateMetadata>>>,
+    metas: RwLock<FxHashMap<CrateNum, Lrc<CrateMetadata>>>,
     /// Map from NodeId's of local extern crate statements to crate numbers
-    extern_mod_crate_map: RefCell<NodeMap<CrateNum>>,
-    pub metadata_loader: Box<MetadataLoader>,
+    extern_mod_crate_map: Lock<NodeMap<CrateNum>>,
+    pub metadata_loader: Box<MetadataLoader + Sync>,
 }
 
 impl CStore {
-    pub fn new(metadata_loader: Box<MetadataLoader>) -> CStore {
+    pub fn new(metadata_loader: Box<MetadataLoader + Sync>) -> CStore {
         CStore {
-            metas: RefCell::new(FxHashMap()),
-            extern_mod_crate_map: RefCell::new(FxHashMap()),
+            metas: RwLock::new(FxHashMap()),
+            extern_mod_crate_map: Lock::new(FxHashMap()),
             metadata_loader,
         }
     }
@@ -110,16 +110,16 @@ impl CStore {
         CrateNum::new(self.metas.borrow().len() + 1)
     }
 
-    pub fn get_crate_data(&self, cnum: CrateNum) -> Rc<CrateMetadata> {
+    pub fn get_crate_data(&self, cnum: CrateNum) -> Lrc<CrateMetadata> {
         self.metas.borrow().get(&cnum).unwrap().clone()
     }
 
-    pub fn set_crate_data(&self, cnum: CrateNum, data: Rc<CrateMetadata>) {
+    pub fn set_crate_data(&self, cnum: CrateNum, data: Lrc<CrateMetadata>) {
         self.metas.borrow_mut().insert(cnum, data);
     }
 
     pub fn iter_crate_data<I>(&self, mut i: I)
-        where I: FnMut(CrateNum, &Rc<CrateMetadata>)
+        where I: FnMut(CrateNum, &Lrc<CrateMetadata>)
     {
         for (&k, v) in self.metas.borrow().iter() {
             i(k, v);
diff --git a/src/librustc_metadata/cstore_impl.rs b/src/librustc_metadata/cstore_impl.rs
index 955648208cd8b..7e6339b0939d5 100644
--- a/src/librustc_metadata/cstore_impl.rs
+++ b/src/librustc_metadata/cstore_impl.rs
@@ -30,7 +30,7 @@ use rustc::hir::map::definitions::DefPathTable;
 use rustc::util::nodemap::{NodeSet, DefIdMap};
 
 use std::any::Any;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use syntax::ast;
 use syntax::attr;
@@ -111,12 +111,12 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         let _ = cdata;
         tcx.calculate_dtor(def_id, &mut |_,_| Ok(()))
     }
-    variances_of => { Rc::new(cdata.get_item_variances(def_id.index)) }
+    variances_of => { Lrc::new(cdata.get_item_variances(def_id.index)) }
     associated_item_def_ids => {
         let mut result = vec![];
         cdata.each_child_of_item(def_id.index,
           |child| result.push(child.def.def_id()), tcx.sess);
-        Rc::new(result)
+        Lrc::new(result)
     }
     associated_item => { cdata.get_associated_item(def_id.index) }
     impl_trait_ref => { cdata.get_impl_trait(def_id.index, tcx) }
@@ -136,11 +136,11 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         mir
     }
     mir_const_qualif => {
-        (cdata.mir_const_qualif(def_id.index), Rc::new(IdxSetBuf::new_empty(0)))
+        (cdata.mir_const_qualif(def_id.index), Lrc::new(IdxSetBuf::new_empty(0)))
     }
     typeck_tables_of => { cdata.item_body_tables(def_id.index, tcx) }
     fn_sig => { cdata.fn_sig(def_id.index, tcx) }
-    inherent_impls => { Rc::new(cdata.get_inherent_implementations_for_type(def_id.index)) }
+    inherent_impls => { Lrc::new(cdata.get_inherent_implementations_for_type(def_id.index)) }
     is_const_fn => { cdata.is_const_fn(def_id.index) }
     is_foreign_item => { cdata.is_foreign_item(def_id.index) }
     is_auto_impl => { cdata.is_auto_impl(def_id.index) }
@@ -169,18 +169,18 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     }
     is_mir_available => { cdata.is_item_mir_available(def_id.index) }
 
-    dylib_dependency_formats => { Rc::new(cdata.get_dylib_dependency_formats()) }
+    dylib_dependency_formats => { Lrc::new(cdata.get_dylib_dependency_formats()) }
     is_panic_runtime => { cdata.is_panic_runtime(tcx.sess) }
     is_compiler_builtins => { cdata.is_compiler_builtins(tcx.sess) }
     has_global_allocator => { cdata.has_global_allocator() }
     is_sanitizer_runtime => { cdata.is_sanitizer_runtime(tcx.sess) }
     is_profiler_runtime => { cdata.is_profiler_runtime(tcx.sess) }
     panic_strategy => { cdata.panic_strategy() }
-    extern_crate => { Rc::new(cdata.extern_crate.get()) }
+    extern_crate => { Lrc::new(cdata.extern_crate.get()) }
     is_no_builtins => { cdata.is_no_builtins(tcx.sess) }
     impl_defaultness => { cdata.get_impl_defaultness(def_id.index) }
-    exported_symbol_ids => { Rc::new(cdata.get_exported_symbols()) }
-    native_libraries => { Rc::new(cdata.get_native_libraries(tcx.sess)) }
+    exported_symbol_ids => { Lrc::new(cdata.get_exported_symbols()) }
+    native_libraries => { Lrc::new(cdata.get_native_libraries(tcx.sess)) }
     plugin_registrar_fn => {
         cdata.root.plugin_registrar_fn.map(|index| {
             DefId { krate: def_id.krate, index }
@@ -199,13 +199,13 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         let mut result = vec![];
         let filter = Some(other);
         cdata.get_implementations_for_trait(filter, &mut result);
-        Rc::new(result)
+        Lrc::new(result)
     }
 
     all_trait_implementations => {
         let mut result = vec![];
         cdata.get_implementations_for_trait(None, &mut result);
-        Rc::new(result)
+        Lrc::new(result)
     }
 
     is_dllimport_foreign_item => {
@@ -217,10 +217,10 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     item_children => {
         let mut result = vec![];
         cdata.each_child_of_item(def_id.index, |child| result.push(child), tcx.sess);
-        Rc::new(result)
+        Lrc::new(result)
     }
-    defined_lang_items => { Rc::new(cdata.get_lang_items()) }
-    missing_lang_items => { Rc::new(cdata.get_missing_lang_items()) }
+    defined_lang_items => { Lrc::new(cdata.get_lang_items()) }
+    missing_lang_items => { Lrc::new(cdata.get_missing_lang_items()) }
 
     extern_const_body => {
         debug!("item_body({:?}): inlining item", def_id);
@@ -234,7 +234,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         }
     }
 
-    used_crate_source => { Rc::new(cdata.source.clone()) }
+    used_crate_source => { Lrc::new(cdata.source.clone()) }
 
     has_copy_closures => { cdata.has_copy_closures(tcx.sess) }
     has_clone_closures => { cdata.has_clone_closures(tcx.sess) }
@@ -276,11 +276,11 @@ pub fn provide<'tcx>(providers: &mut Providers<'tcx>) {
         },
         native_libraries: |tcx, cnum| {
             assert_eq!(cnum, LOCAL_CRATE);
-            Rc::new(native_libs::collect(tcx))
+            Lrc::new(native_libs::collect(tcx))
         },
         link_args: |tcx, cnum| {
             assert_eq!(cnum, LOCAL_CRATE);
-            Rc::new(link_args::collect(tcx))
+            Lrc::new(link_args::collect(tcx))
         },
 
         // Returns a map from a sufficiently visible external item (i.e. an
@@ -362,7 +362,7 @@ pub fn provide<'tcx>(providers: &mut Providers<'tcx>) {
                 }
             }
 
-            Rc::new(visible_parent_map)
+            Lrc::new(visible_parent_map)
         },
 
         ..*providers
@@ -370,7 +370,7 @@ pub fn provide<'tcx>(providers: &mut Providers<'tcx>) {
 }
 
 impl CrateStore for cstore::CStore {
-    fn crate_data_as_rc_any(&self, krate: CrateNum) -> Rc<Any> {
+    fn crate_data_as_rc_any(&self, krate: CrateNum) -> Lrc<Any> {
         self.get_crate_data(krate)
     }
 
@@ -443,7 +443,7 @@ impl CrateStore for cstore::CStore {
         self.get_crate_data(def.krate).def_path_hash(def.index)
     }
 
-    fn def_path_table(&self, cnum: CrateNum) -> Rc<DefPathTable> {
+    fn def_path_table(&self, cnum: CrateNum) -> Lrc<DefPathTable> {
         self.get_crate_data(cnum).def_path_table.clone()
     }
 
@@ -467,7 +467,7 @@ impl CrateStore for cstore::CStore {
         } else if data.name == "proc_macro" &&
                   self.get_crate_data(id.krate).item_name(id.index) == "quote" {
             let ext = SyntaxExtension::ProcMacro(Box::new(::proc_macro::__internal::Quoter));
-            return LoadedMacro::ProcMacro(Rc::new(ext));
+            return LoadedMacro::ProcMacro(Lrc::new(ext));
         }
 
         let (name, def) = data.get_macro(id.index);
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index 0e9f4a8f1784b..09a8e1c785ab1 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -13,6 +13,7 @@
 use cstore::{self, CrateMetadata, MetadataBlob, NativeLibrary};
 use schema::*;
 
+use rustc_data_structures::sync::{Lrc, ReadGuard};
 use rustc::hir::map::{DefKey, DefPath, DefPathData, DefPathHash};
 use rustc::hir;
 use rustc::middle::cstore::{LinkagePreference, ExternConstBody,
@@ -28,11 +29,9 @@ use rustc::ty::codec::TyDecoder;
 use rustc::util::nodemap::DefIdSet;
 use rustc::mir::Mir;
 
-use std::cell::Ref;
 use std::collections::BTreeMap;
 use std::io;
 use std::mem;
-use std::rc::Rc;
 use std::u32;
 
 use rustc_serialize::{Decodable, Decoder, SpecializedDecoder, opaque};
@@ -775,12 +774,12 @@ impl<'a, 'tcx> CrateMetadata {
                                                    .map(|body| (body.id(), body))
                                                    .collect();
             ExternBodyNestedBodies {
-                nested_bodies: Rc::new(nested_bodies),
+                nested_bodies: Lrc::new(nested_bodies),
                 fingerprint: ast.stable_bodies_hash,
             }
         } else {
             ExternBodyNestedBodies {
-                nested_bodies: Rc::new(BTreeMap::new()),
+                nested_bodies: Lrc::new(BTreeMap::new()),
                 fingerprint: Fingerprint::zero(),
             }
         }
@@ -870,11 +869,11 @@ impl<'a, 'tcx> CrateMetadata {
         }
     }
 
-    pub fn get_item_attrs(&self, node_id: DefIndex, sess: &Session) -> Rc<[ast::Attribute]> {
+    pub fn get_item_attrs(&self, node_id: DefIndex, sess: &Session) -> Lrc<[ast::Attribute]> {
         let (node_as, node_index) =
             (node_id.address_space().index(), node_id.as_array_index());
         if self.is_proc_macro(node_id) {
-            return Rc::new([]);
+            return Lrc::new([]);
         }
 
         if let Some(&Some(ref val)) =
@@ -890,7 +889,7 @@ impl<'a, 'tcx> CrateMetadata {
         if def_key.disambiguated_data.data == DefPathData::StructCtor {
             item = self.entry(def_key.parent.unwrap());
         }
-        let result: Rc<[ast::Attribute]> = Rc::from(self.get_attributes(&item, sess));
+        let result: Lrc<[ast::Attribute]> = Lrc::from(self.get_attributes(&item, sess));
         let vec_ = &mut self.attribute_cache.borrow_mut()[node_as];
         if vec_.len() < node_index + 1 {
             vec_.resize(node_index + 1, None);
@@ -1108,7 +1107,7 @@ impl<'a, 'tcx> CrateMetadata {
     /// for items inlined from other crates.
     pub fn imported_filemaps(&'a self,
                              local_codemap: &codemap::CodeMap)
-                             -> Ref<'a, Vec<cstore::ImportedFileMap>> {
+                             -> ReadGuard<'a, Vec<cstore::ImportedFileMap>> {
         {
             let filemaps = self.codemap_import_info.borrow();
             if !filemaps.is_empty() {
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index 5ddbb18450e2e..411de16e9b49b 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -35,7 +35,7 @@ use std::hash::Hash;
 use std::io::prelude::*;
 use std::io::Cursor;
 use std::path::Path;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::u32;
 use syntax::ast::{self, CRATE_NODE_ID};
 use syntax::codemap::Spanned;
@@ -297,7 +297,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                                 adapted.name.hash(&mut hasher);
                                 hasher.finish()
                             };
-                            Rc::new(adapted)
+                            Lrc::new(adapted)
                         }
                     },
                     // expanded code, not from a file
diff --git a/src/librustc_metadata/lib.rs b/src/librustc_metadata/lib.rs
index a65ddcecf8874..169a2f3a10f02 100644
--- a/src/librustc_metadata/lib.rs
+++ b/src/librustc_metadata/lib.rs
@@ -23,7 +23,10 @@
 #![feature(specialization)]
 #![feature(rustc_private)]
 
+#![recursion_limit="256"]
+
 extern crate libc;
+
 #[macro_use]
 extern crate log;
 #[macro_use]
diff --git a/src/librustc_metadata/locator.rs b/src/librustc_metadata/locator.rs
index 90c469eea843d..dee8af9a8be50 100644
--- a/src/librustc_metadata/locator.rs
+++ b/src/librustc_metadata/locator.rs
@@ -219,7 +219,7 @@
 //! no means all of the necessary details. Take a look at the rest of
 //! metadata::locator or metadata::creader for all the juicy details!
 
-use cstore::MetadataBlob;
+use cstore::{MetadataRef, MetadataBlob};
 use creader::Library;
 use schema::{METADATA_HEADER, rustc_version};
 
@@ -243,8 +243,8 @@ use std::path::{Path, PathBuf};
 use std::time::Instant;
 
 use flate2::read::DeflateDecoder;
-use rustc_data_structures::owning_ref::{ErasedBoxRef, OwningRef};
 
+use rustc_data_structures::owning_ref::OwningRef;
 pub struct CrateMismatch {
     path: PathBuf,
     got: String,
@@ -842,7 +842,7 @@ fn get_metadata_section_imp(target: &Target,
     if !filename.exists() {
         return Err(format!("no such file: '{}'", filename.display()));
     }
-    let raw_bytes: ErasedBoxRef<[u8]> = match flavor {
+    let raw_bytes: MetadataRef = match flavor {
         CrateFlavor::Rlib => loader.get_rlib_metadata(target, filename)?,
         CrateFlavor::Dylib => {
             let buf = loader.get_dylib_metadata(target, filename)?;
diff --git a/src/librustc_mir/borrow_check/error_reporting.rs b/src/librustc_mir/borrow_check/error_reporting.rs
index bc1b3edbb6ad9..c2b0299dca034 100644
--- a/src/librustc_mir/borrow_check/error_reporting.rs
+++ b/src/librustc_mir/borrow_check/error_reporting.rs
@@ -14,8 +14,7 @@ use rustc::mir::{BorrowKind, Field, Local, Location, Operand};
 use rustc::mir::{Place, ProjectionElem, Rvalue, Statement, StatementKind};
 use rustc::ty::{self, RegionKind};
 use rustc_data_structures::indexed_vec::Idx;
-
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use super::{MirBorrowckCtxt, Context};
 use super::{InitializationRequiringAction, PrefixSet};
@@ -426,7 +425,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         &mut self,
         context: Context,
         name: &String,
-        _scope_tree: &Rc<ScopeTree>,
+        _scope_tree: &Lrc<ScopeTree>,
         borrow: &BorrowData<'tcx>,
         drop_span: Span,
         borrow_span: Span,
@@ -448,7 +447,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
     fn report_scoped_temporary_value_does_not_live_long_enough(
         &mut self,
         context: Context,
-        _scope_tree: &Rc<ScopeTree>,
+        _scope_tree: &Lrc<ScopeTree>,
         borrow: &BorrowData<'tcx>,
         drop_span: Span,
         _borrow_span: Span,
@@ -472,7 +471,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         &mut self,
         context: Context,
         name: &String,
-        scope_tree: &Rc<ScopeTree>,
+        scope_tree: &Lrc<ScopeTree>,
         borrow: &BorrowData<'tcx>,
         drop_span: Span,
         borrow_span: Span,
@@ -494,7 +493,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
     fn report_unscoped_temporary_value_does_not_live_long_enough(
         &mut self,
         context: Context,
-        scope_tree: &Rc<ScopeTree>,
+        scope_tree: &Lrc<ScopeTree>,
         borrow: &BorrowData<'tcx>,
         drop_span: Span,
         _borrow_span: Span,
diff --git a/src/librustc_mir/dataflow/impls/borrows.rs b/src/librustc_mir/dataflow/impls/borrows.rs
index c39ae10371cdd..d1125f541de44 100644
--- a/src/librustc_mir/dataflow/impls/borrows.rs
+++ b/src/librustc_mir/dataflow/impls/borrows.rs
@@ -22,6 +22,7 @@ use rustc::util::nodemap::{FxHashMap, FxHashSet};
 use rustc_data_structures::bitslice::{BitwiseOperator};
 use rustc_data_structures::indexed_set::{IdxSet};
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
+use rustc_data_structures::sync::Lrc;
 
 use dataflow::{BitDenotation, BlockSets, InitialFlow};
 pub use dataflow::indexes::{BorrowIndex, ReserveOrActivateIndex};
@@ -44,7 +45,7 @@ use std::rc::Rc;
 pub struct Borrows<'a, 'gcx: 'tcx, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'gcx, 'tcx>,
     mir: &'a Mir<'tcx>,
-    scope_tree: Rc<region::ScopeTree>,
+    scope_tree: Lrc<region::ScopeTree>,
     root_scope: Option<region::Scope>,
 
     /// The fundamental map relating bitvector indexes to the borrows
@@ -273,7 +274,7 @@ impl<'a, 'gcx, 'tcx> Borrows<'a, 'gcx, 'tcx> {
 
     pub fn borrows(&self) -> &IndexVec<BorrowIndex, BorrowData<'tcx>> { &self.borrows }
 
-    pub fn scope_tree(&self) -> &Rc<region::ScopeTree> { &self.scope_tree }
+    pub fn scope_tree(&self) -> &Lrc<region::ScopeTree> { &self.scope_tree }
 
     pub fn location(&self, idx: BorrowIndex) -> &Location {
         &self.borrows[idx].location
diff --git a/src/librustc_mir/hair/cx/mod.rs b/src/librustc_mir/hair/cx/mod.rs
index 306b41714a553..c331eef6f49ec 100644
--- a/src/librustc_mir/hair/cx/mod.rs
+++ b/src/librustc_mir/hair/cx/mod.rs
@@ -30,7 +30,7 @@ use syntax::ast;
 use syntax::symbol::Symbol;
 use rustc::hir;
 use rustc_const_math::{ConstInt, ConstUsize};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 #[derive(Clone)]
 pub struct Cx<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
@@ -43,7 +43,7 @@ pub struct Cx<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     /// Identity `Substs` for use with const-evaluation.
     pub identity_substs: &'gcx Substs<'gcx>,
 
-    pub region_scope_tree: Rc<region::ScopeTree>,
+    pub region_scope_tree: Lrc<region::ScopeTree>,
     pub tables: &'a ty::TypeckTables<'gcx>,
 
     /// This is `Constness::Const` if we are compiling a `static`,
diff --git a/src/librustc_mir/transform/check_unsafety.rs b/src/librustc_mir/transform/check_unsafety.rs
index e7ce528507180..d3b867685d610 100644
--- a/src/librustc_mir/transform/check_unsafety.rs
+++ b/src/librustc_mir/transform/check_unsafety.rs
@@ -10,6 +10,7 @@
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::indexed_vec::IndexVec;
+use rustc_data_structures::sync::Lrc;
 
 use rustc::ty::maps::Providers;
 use rustc::ty::{self, TyCtxt};
@@ -22,7 +23,6 @@ use rustc::mir::visit::{PlaceContext, Visitor};
 use syntax::ast;
 use syntax::symbol::Symbol;
 
-use std::rc::Rc;
 use util;
 
 pub struct UnsafetyChecker<'a, 'tcx: 'a> {
@@ -328,8 +328,8 @@ fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
         ClearCrossCrate::Clear => {
             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
             return UnsafetyCheckResult {
-                violations: Rc::new([]),
-                unsafe_blocks: Rc::new([])
+                violations: Lrc::new([]),
+                unsafe_blocks: Lrc::new([])
             }
         }
     };
diff --git a/src/librustc_mir/transform/mod.rs b/src/librustc_mir/transform/mod.rs
index 563405fccc970..daa93dc744568 100644
--- a/src/librustc_mir/transform/mod.rs
+++ b/src/librustc_mir/transform/mod.rs
@@ -18,8 +18,8 @@ use rustc::ty::steal::Steal;
 use rustc::hir;
 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
 use rustc::util::nodemap::DefIdSet;
+use rustc_data_structures::sync::Lrc;
 use std::borrow::Cow;
-use std::rc::Rc;
 use syntax::ast;
 use syntax_pos::Span;
 
@@ -66,7 +66,7 @@ fn is_mir_available<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> boo
 /// Finds the full set of def-ids within the current crate that have
 /// MIR associated with them.
 fn mir_keys<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, krate: CrateNum)
-                      -> Rc<DefIdSet> {
+                      -> Lrc<DefIdSet> {
     assert_eq!(krate, LOCAL_CRATE);
 
     let mut set = DefIdSet();
@@ -101,7 +101,7 @@ fn mir_keys<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, krate: CrateNum)
         set: &mut set,
     }.as_deep_visitor());
 
-    Rc::new(set)
+    Lrc::new(set)
 }
 
 fn mir_built<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx Steal<Mir<'tcx>> {
diff --git a/src/librustc_mir/transform/qualify_consts.rs b/src/librustc_mir/transform/qualify_consts.rs
index 2b2323928efba..cfd7cf0313da6 100644
--- a/src/librustc_mir/transform/qualify_consts.rs
+++ b/src/librustc_mir/transform/qualify_consts.rs
@@ -34,7 +34,7 @@ use syntax::feature_gate::UnstableFeatures;
 use syntax_pos::{Span, DUMMY_SP};
 
 use std::fmt;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::usize;
 
 use transform::{MirPass, MirSource};
@@ -296,7 +296,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
     }
 
     /// Qualify a whole const, static initializer or const fn.
-    fn qualify_const(&mut self) -> (Qualif, Rc<IdxSetBuf<Local>>) {
+    fn qualify_const(&mut self) -> (Qualif, Lrc<IdxSetBuf<Local>>) {
         debug!("qualifying {} {:?}", self.mode, self.def_id);
 
         let mir = self.mir;
@@ -411,7 +411,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
             }
         }
 
-        (self.qualif, Rc::new(promoted_temps))
+        (self.qualif, Lrc::new(promoted_temps))
     }
 }
 
@@ -945,7 +945,7 @@ pub fn provide(providers: &mut Providers) {
 
 fn mir_const_qualif<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                               def_id: DefId)
-                              -> (u8, Rc<IdxSetBuf<Local>>) {
+                              -> (u8, Lrc<IdxSetBuf<Local>>) {
     // NB: This `borrow()` is guaranteed to be valid (i.e., the value
     // cannot yet be stolen), because `mir_validated()`, which steals
     // from `mir_const(), forces this query to execute before
@@ -954,7 +954,7 @@ fn mir_const_qualif<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     if mir.return_ty().references_error() {
         tcx.sess.delay_span_bug(mir.span, "mir_const_qualif: Mir had errors");
-        return (Qualif::NOT_CONST.bits(), Rc::new(IdxSetBuf::new_empty(0)));
+        return (Qualif::NOT_CONST.bits(), Lrc::new(IdxSetBuf::new_empty(0)));
     }
 
     let mut qualifier = Qualifier::new(tcx, def_id, mir, Mode::Const);
diff --git a/src/librustc_passes/Cargo.toml b/src/librustc_passes/Cargo.toml
index d2560c2f8203f..c2e5e369a8fcb 100644
--- a/src/librustc_passes/Cargo.toml
+++ b/src/librustc_passes/Cargo.toml
@@ -13,6 +13,7 @@ log = "0.3"
 rustc = { path = "../librustc" }
 rustc_const_eval = { path = "../librustc_const_eval" }
 rustc_const_math = { path = "../librustc_const_math" }
+rustc_data_structures = { path = "../librustc_data_structures" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc_errors = { path = "../librustc_errors" }
diff --git a/src/librustc_passes/consts.rs b/src/librustc_passes/consts.rs
index 6df860492f05a..74d548c1fbb95 100644
--- a/src/librustc_passes/consts.rs
+++ b/src/librustc_passes/consts.rs
@@ -45,7 +45,7 @@ use rustc::util::common::ErrorReported;
 use rustc::util::nodemap::{ItemLocalSet, NodeSet};
 use rustc::lint::builtin::CONST_ERR;
 use rustc::hir::{self, PatKind, RangeEnd};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax_pos::{Span, DUMMY_SP};
 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
@@ -83,7 +83,7 @@ fn const_is_rvalue_promotable_to_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                    def_id: DefId)
-                                   -> Rc<ItemLocalSet>
+                                   -> Lrc<ItemLocalSet>
 {
     let outer_def_id = tcx.closure_base_def_id(def_id);
     if outer_def_id != def_id {
@@ -108,7 +108,7 @@ fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let body_id = tcx.hir.body_owned_by(node_id);
     visitor.visit_nested_body(body_id);
 
-    Rc::new(visitor.result)
+    Lrc::new(visitor.result)
 }
 
 struct CheckCrateVisitor<'a, 'tcx: 'a> {
diff --git a/src/librustc_passes/lib.rs b/src/librustc_passes/lib.rs
index 9a150abea6691..9e7f2e142a360 100644
--- a/src/librustc_passes/lib.rs
+++ b/src/librustc_passes/lib.rs
@@ -25,6 +25,7 @@
 extern crate rustc;
 extern crate rustc_const_eval;
 extern crate rustc_const_math;
+extern crate rustc_data_structures;
 
 #[macro_use]
 extern crate log;
diff --git a/src/librustc_privacy/Cargo.toml b/src/librustc_privacy/Cargo.toml
index c65312e9a8337..62eab40f3ec9a 100644
--- a/src/librustc_privacy/Cargo.toml
+++ b/src/librustc_privacy/Cargo.toml
@@ -13,3 +13,4 @@ rustc = { path = "../librustc" }
 rustc_typeck = { path = "../librustc_typeck" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
+rustc_data_structures = { path = "../librustc_data_structures" }
\ No newline at end of file
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index bb0a4be49c2a8..b36b140a881d5 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -19,6 +19,7 @@
 #[macro_use] extern crate syntax;
 extern crate rustc_typeck;
 extern crate syntax_pos;
+extern crate rustc_data_structures;
 
 use rustc::hir::{self, PatKind};
 use rustc::hir::def::Def;
@@ -37,7 +38,7 @@ use syntax_pos::Span;
 
 use std::cmp;
 use std::mem::replace;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 mod diagnostics;
 
@@ -1642,13 +1643,13 @@ pub fn provide(providers: &mut Providers) {
     };
 }
 
-pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Rc<AccessLevels> {
+pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Lrc<AccessLevels> {
     tcx.privacy_access_levels(LOCAL_CRATE)
 }
 
 fn privacy_access_levels<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                    krate: CrateNum)
-                                   -> Rc<AccessLevels> {
+                                   -> Lrc<AccessLevels> {
     assert_eq!(krate, LOCAL_CRATE);
 
     let krate = tcx.hir.krate();
@@ -1722,7 +1723,7 @@ fn privacy_access_levels<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         krate.visit_all_item_likes(&mut DeepVisitor::new(&mut visitor));
     }
 
-    Rc::new(visitor.access_levels)
+    Lrc::new(visitor.access_levels)
 }
 
 __build_diagnostic_array! { librustc_privacy, DIAGNOSTICS }
diff --git a/src/librustc_resolve/build_reduced_graph.rs b/src/librustc_resolve/build_reduced_graph.rs
index 3b20c1e74cd39..efd28326a22a1 100644
--- a/src/librustc_resolve/build_reduced_graph.rs
+++ b/src/librustc_resolve/build_reduced_graph.rs
@@ -27,7 +27,7 @@ use rustc::hir::def_id::{BUILTIN_MACROS_CRATE, CRATE_DEF_INDEX, LOCAL_CRATE, Def
 use rustc::ty;
 
 use std::cell::Cell;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use syntax::ast::{Name, Ident};
 use syntax::attr;
@@ -576,7 +576,7 @@ impl<'a> Resolver<'a> {
         }
     }
 
-    pub fn get_macro(&mut self, def: Def) -> Rc<SyntaxExtension> {
+    pub fn get_macro(&mut self, def: Def) -> Lrc<SyntaxExtension> {
         let def_id = match def {
             Def::Macro(def_id, ..) => def_id,
             _ => panic!("Expected Def::Macro(..)"),
@@ -590,7 +590,7 @@ impl<'a> Resolver<'a> {
             LoadedMacro::ProcMacro(ext) => return ext,
         };
 
-        let ext = Rc::new(macro_rules::compile(&self.session.parse_sess,
+        let ext = Lrc::new(macro_rules::compile(&self.session.parse_sess,
                                                &self.session.features,
                                                &macro_def));
         self.macro_map.insert(def_id, ext.clone());
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index b57a8bc7e77f1..3391861665915 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -68,7 +68,7 @@ use std::cmp;
 use std::collections::BTreeSet;
 use std::fmt;
 use std::mem::replace;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use resolve_imports::{ImportDirective, ImportDirectiveSubclass, NameResolution, ImportResolver};
 use macros::{InvocationData, LegacyBinding, LegacyScope, MacroBinding};
@@ -1118,7 +1118,7 @@ impl<'a> NameBinding<'a> {
         }
     }
 
-    fn get_macro(&self, resolver: &mut Resolver<'a>) -> Rc<SyntaxExtension> {
+    fn get_macro(&self, resolver: &mut Resolver<'a>) -> Lrc<SyntaxExtension> {
         resolver.get_macro(self.def_ignoring_ambiguity())
     }
 
@@ -1323,7 +1323,7 @@ pub struct Resolver<'a> {
     macro_names: FxHashSet<Ident>,
     global_macros: FxHashMap<Name, &'a NameBinding<'a>>,
     lexical_macro_resolutions: Vec<(Ident, &'a Cell<LegacyScope<'a>>)>,
-    macro_map: FxHashMap<DefId, Rc<SyntaxExtension>>,
+    macro_map: FxHashMap<DefId, Lrc<SyntaxExtension>>,
     macro_defs: FxHashMap<Mark, DefId>,
     local_macro_def_scopes: FxHashMap<NodeId, Module<'a>>,
     macro_exports: Vec<Export>,
diff --git a/src/librustc_resolve/macros.rs b/src/librustc_resolve/macros.rs
index 260a0cd7cd733..a3f5fa3db2f5c 100644
--- a/src/librustc_resolve/macros.rs
+++ b/src/librustc_resolve/macros.rs
@@ -40,7 +40,7 @@ use syntax_pos::{Span, DUMMY_SP};
 
 use std::cell::Cell;
 use std::mem;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 #[derive(Clone)]
 pub struct InvocationData<'a> {
@@ -185,7 +185,7 @@ impl<'a> base::Resolver for Resolver<'a> {
         invocation.expansion.set(visitor.legacy_scope);
     }
 
-    fn add_builtin(&mut self, ident: ast::Ident, ext: Rc<SyntaxExtension>) {
+    fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>) {
         let def_id = DefId {
             krate: BUILTIN_MACROS_CRATE,
             index: DefIndex::new(self.macro_map.len()),
@@ -292,7 +292,7 @@ impl<'a> base::Resolver for Resolver<'a> {
     }
 
     fn resolve_invoc(&mut self, invoc: &mut Invocation, scope: Mark, force: bool)
-                     -> Result<Option<Rc<SyntaxExtension>>, Determinacy> {
+                     -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
         let def = match invoc.kind {
             InvocationKind::Attr { attr: None, .. } => return Ok(None),
             _ => self.resolve_invoc_to_def(invoc, scope, force)?,
@@ -315,7 +315,7 @@ impl<'a> base::Resolver for Resolver<'a> {
     }
 
     fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
-                     -> Result<Rc<SyntaxExtension>, Determinacy> {
+                     -> Result<Lrc<SyntaxExtension>, Determinacy> {
         self.resolve_macro_to_def(scope, path, kind, force).map(|def| {
             self.unused_macros.remove(&def.def_id());
             self.get_macro(def)
@@ -735,7 +735,7 @@ impl<'a> Resolver<'a> {
         }
 
         let def_id = self.definitions.local_def_id(item.id);
-        let ext = Rc::new(macro_rules::compile(&self.session.parse_sess,
+        let ext = Lrc::new(macro_rules::compile(&self.session.parse_sess,
                                                &self.session.features,
                                                item));
         self.macro_map.insert(def_id, ext);
diff --git a/src/librustc_trans/back/symbol_export.rs b/src/librustc_trans/back/symbol_export.rs
index fa6fe2e9e93ef..121361a9ef48e 100644
--- a/src/librustc_trans/back/symbol_export.rs
+++ b/src/librustc_trans/back/symbol_export.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::sync::Arc;
 
 use base;
@@ -64,7 +64,7 @@ pub fn crates_export_threshold(crate_types: &[config::CrateType])
 pub fn provide(providers: &mut Providers) {
     providers.exported_symbol_ids = |tcx, cnum| {
         let export_threshold = threshold(tcx);
-        Rc::new(tcx.exported_symbols(cnum)
+        Lrc::new(tcx.exported_symbols(cnum)
             .iter()
             .filter_map(|&(_, id, level)| {
                 id.and_then(|id| {
diff --git a/src/librustc_trans/back/write.rs b/src/librustc_trans/back/write.rs
index d8e95cd2cf2e0..147a79ef4cb88 100644
--- a/src/librustc_trans/back/write.rs
+++ b/src/librustc_trans/back/write.rs
@@ -982,7 +982,7 @@ pub fn start_async_translation(tcx: TyCtxt,
         crate_info,
 
         time_graph,
-        coordinator_send: tcx.tx_to_llvm_workers.clone(),
+        coordinator_send: tcx.tx_to_llvm_workers.lock().clone(),
         trans_worker_receive,
         shared_emitter_main,
         future: coordinator_thread,
@@ -1352,7 +1352,7 @@ fn start_executing_work(tcx: TyCtxt,
                         metadata_config: Arc<ModuleConfig>,
                         allocator_config: Arc<ModuleConfig>)
                         -> thread::JoinHandle<Result<CompiledModules, ()>> {
-    let coordinator_send = tcx.tx_to_llvm_workers.clone();
+    let coordinator_send = tcx.tx_to_llvm_workers.lock().clone();
     let mut exported_symbols = FxHashMap();
     exported_symbols.insert(LOCAL_CRATE, tcx.exported_symbols(LOCAL_CRATE));
     for &cnum in tcx.crates().iter() {
@@ -2257,7 +2257,7 @@ pub fn submit_translated_module_to_llvm(tcx: TyCtxt,
                                         mtrans: ModuleTranslation,
                                         cost: u64) {
     let llvm_work_item = WorkItem::Optimize(mtrans);
-    drop(tcx.tx_to_llvm_workers.send(Box::new(Message::TranslationDone {
+    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::TranslationDone {
         llvm_work_item,
         cost,
     })));
diff --git a/src/librustc_trans/lib.rs b/src/librustc_trans/lib.rs
index c4849c621e8d5..380b56b50ef90 100644
--- a/src/librustc_trans/lib.rs
+++ b/src/librustc_trans/lib.rs
@@ -73,8 +73,8 @@ pub use llvm_util::{init, target_features, print_version, print_passes, print, e
 
 use std::any::Any;
 use std::path::PathBuf;
-use std::rc::Rc;
 use std::sync::mpsc;
+use rustc_data_structures::sync::{self, Lrc};
 
 use rustc::dep_graph::DepGraph;
 use rustc::hir::def_id::CrateNum;
@@ -158,7 +158,7 @@ impl rustc_trans_utils::trans_crate::TransCrate for LlvmTransCrate {
     type OngoingCrateTranslation = back::write::OngoingCrateTranslation;
     type TranslatedCrate = CrateTranslation;
 
-    fn metadata_loader() -> Box<MetadataLoader> {
+    fn metadata_loader() -> Box<MetadataLoader + sync::Sync> {
         box metadata::LlvmMetadataLoader
     }
 
@@ -319,11 +319,11 @@ pub struct CrateInfo {
     profiler_runtime: Option<CrateNum>,
     sanitizer_runtime: Option<CrateNum>,
     is_no_builtins: FxHashSet<CrateNum>,
-    native_libraries: FxHashMap<CrateNum, Rc<Vec<NativeLibrary>>>,
+    native_libraries: FxHashMap<CrateNum, Lrc<Vec<NativeLibrary>>>,
     crate_name: FxHashMap<CrateNum, String>,
-    used_libraries: Rc<Vec<NativeLibrary>>,
-    link_args: Rc<Vec<String>>,
-    used_crate_source: FxHashMap<CrateNum, Rc<CrateSource>>,
+    used_libraries: Lrc<Vec<NativeLibrary>>,
+    link_args: Lrc<Vec<String>>,
+    used_crate_source: FxHashMap<CrateNum, Lrc<CrateSource>>,
     used_crates_static: Vec<(CrateNum, LibSource)>,
     used_crates_dynamic: Vec<(CrateNum, LibSource)>,
 }
diff --git a/src/librustc_trans_utils/trans_crate.rs b/src/librustc_trans_utils/trans_crate.rs
index 800c3063c025c..5ac9f2c7f146f 100644
--- a/src/librustc_trans_utils/trans_crate.rs
+++ b/src/librustc_trans_utils/trans_crate.rs
@@ -28,7 +28,7 @@ use std::fs::File;
 use std::path::Path;
 use std::sync::mpsc;
 
-use rustc_data_structures::owning_ref::{ErasedBoxRef, OwningRef};
+use rustc_data_structures::owning_ref::OwningRef;
 use ar::{Archive, Builder, Header};
 use flate2::Compression;
 use flate2::write::DeflateEncoder;
@@ -39,18 +39,21 @@ use rustc::session::Session;
 use rustc::session::config::{CrateType, OutputFilenames};
 use rustc::ty::TyCtxt;
 use rustc::ty::maps::Providers;
-use rustc::middle::cstore::EncodedMetadata;
+use rustc::middle::cstore::{MetadataLoader, EncodedMetadata};
 use rustc::middle::cstore::MetadataLoader as MetadataLoaderTrait;
 use rustc::dep_graph::{DepGraph, DepNode, DepKind};
 use rustc_back::target::Target;
 use link::{build_link_meta, out_filename};
+use rustc_data_structures::sync::Sync;
+
+pub use rustc_data_structures::sync::MetadataRef;
 
 pub trait TransCrate {
     type MetadataLoader: MetadataLoaderTrait;
     type OngoingCrateTranslation;
     type TranslatedCrate;
 
-    fn metadata_loader() -> Box<MetadataLoaderTrait>;
+    fn metadata_loader() -> Box<MetadataLoader + Sync>;
     fn provide(_providers: &mut Providers);
     fn provide_extern(_providers: &mut Providers);
     fn trans_crate<'a, 'tcx>(
@@ -73,7 +76,7 @@ impl TransCrate for DummyTransCrate {
     type OngoingCrateTranslation = ();
     type TranslatedCrate = ();
 
-    fn metadata_loader() -> Box<MetadataLoaderTrait> {
+    fn metadata_loader() -> Box<MetadataLoader + Sync> {
         box DummyMetadataLoader(())
     }
 
@@ -116,7 +119,7 @@ impl MetadataLoaderTrait for DummyMetadataLoader {
         &self,
         _target: &Target,
         _filename: &Path
-    ) -> Result<ErasedBoxRef<[u8]>, String> {
+    ) -> Result<MetadataRef, String> {
         bug!("DummyMetadataLoader::get_rlib_metadata");
     }
 
@@ -124,7 +127,7 @@ impl MetadataLoaderTrait for DummyMetadataLoader {
         &self,
         _target: &Target,
         _filename: &Path
-    ) -> Result<ErasedBoxRef<[u8]>, String> {
+    ) -> Result<MetadataRef, String> {
         bug!("DummyMetadataLoader::get_dylib_metadata");
     }
 }
@@ -132,7 +135,7 @@ impl MetadataLoaderTrait for DummyMetadataLoader {
 pub struct NoLlvmMetadataLoader;
 
 impl MetadataLoaderTrait for NoLlvmMetadataLoader {
-    fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<ErasedBoxRef<[u8]>, String> {
+    fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<MetadataRef, String> {
         let file = File::open(filename)
             .map_err(|e| format!("metadata file open err: {:?}", e))?;
         let mut archive = Archive::new(file);
@@ -155,7 +158,7 @@ impl MetadataLoaderTrait for NoLlvmMetadataLoader {
         &self,
         _target: &Target,
         _filename: &Path,
-    ) -> Result<ErasedBoxRef<[u8]>, String> {
+    ) -> Result<MetadataRef, String> {
         // FIXME: Support reading dylibs from llvm enabled rustc
         self.get_rlib_metadata(_target, _filename)
     }
@@ -181,7 +184,7 @@ impl TransCrate for MetadataOnlyTransCrate {
     type OngoingCrateTranslation = OngoingCrateTranslation;
     type TranslatedCrate = TranslatedCrate;
 
-    fn metadata_loader() -> Box<MetadataLoaderTrait> {
+    fn metadata_loader() -> Box<MetadataLoader + Sync> {
         box NoLlvmMetadataLoader
     }
 
diff --git a/src/librustc_typeck/check/generator_interior.rs b/src/librustc_typeck/check/generator_interior.rs
index af1297697c241..268930c05b141 100644
--- a/src/librustc_typeck/check/generator_interior.rs
+++ b/src/librustc_typeck/check/generator_interior.rs
@@ -18,14 +18,14 @@ use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
 use rustc::hir::{self, Pat, PatKind, Expr};
 use rustc::middle::region;
 use rustc::ty::Ty;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use super::FnCtxt;
 use util::nodemap::FxHashMap;
 
 struct InteriorVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
     types: FxHashMap<Ty<'tcx>, usize>,
-    region_scope_tree: Rc<region::ScopeTree>,
+    region_scope_tree: Lrc<region::ScopeTree>,
     expr_count: usize,
 }
 
diff --git a/src/librustc_typeck/check/method/mod.rs b/src/librustc_typeck/check/method/mod.rs
index 58d72e37d51cf..b87b61bbaf688 100644
--- a/src/librustc_typeck/check/method/mod.rs
+++ b/src/librustc_typeck/check/method/mod.rs
@@ -25,7 +25,7 @@ use syntax_pos::Span;
 
 use rustc::hir;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 pub use self::MethodError::*;
 pub use self::CandidateSource::*;
@@ -165,7 +165,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         if let Some(import_id) = pick.import_id {
             let import_def_id = self.tcx.hir.local_def_id(import_id);
             debug!("used_trait_import: {:?}", import_def_id);
-            Rc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
+            Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
                                         .unwrap().insert(import_def_id);
         }
 
@@ -364,7 +364,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         if let Some(import_id) = pick.import_id {
             let import_def_id = self.tcx.hir.local_def_id(import_id);
             debug!("used_trait_import: {:?}", import_def_id);
-            Rc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
+            Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
                                         .unwrap().insert(import_def_id);
         }
 
diff --git a/src/librustc_typeck/check/method/suggest.rs b/src/librustc_typeck/check/method/suggest.rs
index f29009c1973a2..860f7df863f71 100644
--- a/src/librustc_typeck/check/method/suggest.rs
+++ b/src/librustc_typeck/check/method/suggest.rs
@@ -21,6 +21,7 @@ use namespace::Namespace;
 use rustc::traits::{Obligation, SelectionContext};
 use util::nodemap::FxHashSet;
 
+use rustc_data_structures::sync::LockGuard;
 use syntax::ast;
 use errors::DiagnosticBuilder;
 use syntax_pos::Span;
@@ -29,7 +30,6 @@ use rustc::hir;
 use rustc::hir::print;
 use rustc::infer::type_variable::TypeVariableOrigin;
 
-use std::cell;
 use std::cmp::Ordering;
 
 use super::{MethodError, NoMatchData, CandidateSource};
@@ -632,7 +632,7 @@ pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> AllTraits<'a>
 }
 
 pub struct AllTraits<'a> {
-    borrow: cell::Ref<'a, Option<AllTraitsVec>>,
+    borrow: LockGuard<'a, Option<AllTraitsVec>>,
     idx: usize,
 }
 
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index ab81d26e77175..eb85fe7c05c09 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -110,7 +110,7 @@ use util::common::{ErrorReported, indenter};
 use util::nodemap::{DefIdMap, DefIdSet, FxHashMap, NodeMap};
 
 use std::cell::{Cell, RefCell, Ref, RefMut};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::collections::hash_map::Entry;
 use std::cmp;
 use std::fmt::Display;
@@ -797,7 +797,7 @@ fn has_typeck_tables<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn used_trait_imports<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                               def_id: DefId)
-                              -> Rc<DefIdSet> {
+                              -> Lrc<DefIdSet> {
     tcx.typeck_tables_of(def_id).used_trait_imports.clone()
 }
 
diff --git a/src/librustc_typeck/check/regionck.rs b/src/librustc_typeck/check/regionck.rs
index 64063ec5beda9..815ad74b19bfa 100644
--- a/src/librustc_typeck/check/regionck.rs
+++ b/src/librustc_typeck/check/regionck.rs
@@ -96,7 +96,7 @@ use rustc::ty::adjustment;
 
 use std::mem;
 use std::ops::Deref;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax_pos::Span;
 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
@@ -189,7 +189,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
 
-    pub region_scope_tree: Rc<region::ScopeTree>,
+    pub region_scope_tree: Lrc<region::ScopeTree>,
 
     outlives_environment: OutlivesEnvironment<'tcx>,
 
diff --git a/src/librustc_typeck/check/writeback.rs b/src/librustc_typeck/check/writeback.rs
index 29dc983ab560b..4817dfabc2d77 100644
--- a/src/librustc_typeck/check/writeback.rs
+++ b/src/librustc_typeck/check/writeback.rs
@@ -23,7 +23,7 @@ use rustc::util::nodemap::DefIdSet;
 use syntax::ast;
 use syntax_pos::Span;
 use std::mem;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 ///////////////////////////////////////////////////////////////////////////
 // Entry point
@@ -48,7 +48,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         let used_trait_imports = mem::replace(
             &mut self.tables.borrow_mut().used_trait_imports,
-            Rc::new(DefIdSet()),
+            Lrc::new(DefIdSet()),
         );
         debug!(
             "used_trait_imports({:?}) = {:?}",
diff --git a/src/librustc_typeck/coherence/inherent_impls.rs b/src/librustc_typeck/coherence/inherent_impls.rs
index 569b6a2febb45..89f1b8fe4316e 100644
--- a/src/librustc_typeck/coherence/inherent_impls.rs
+++ b/src/librustc_typeck/coherence/inherent_impls.rs
@@ -24,7 +24,7 @@ use rustc::hir::itemlikevisit::ItemLikeVisitor;
 use rustc::ty::{self, CrateInherentImpls, TyCtxt};
 use rustc::util::nodemap::DefIdMap;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax_pos::Span;
 
@@ -48,7 +48,7 @@ pub fn crate_inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 /// On-demand query: yields a vector of the inherent impls for a specific type.
 pub fn inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 ty_def_id: DefId)
-                                -> Rc<Vec<DefId>> {
+                                -> Lrc<Vec<DefId>> {
     assert!(ty_def_id.is_local());
 
     // NB. Until we adopt the red-green dep-tracking algorithm (see
@@ -67,7 +67,7 @@ pub fn inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     // [the plan]: https://github.com/rust-lang/rust-roadmap/issues/4
 
     thread_local! {
-        static EMPTY_DEF_ID_VEC: Rc<Vec<DefId>> = Rc::new(vec![])
+        static EMPTY_DEF_ID_VEC: Lrc<Vec<DefId>> = Lrc::new(vec![])
     }
 
     let result = tcx.dep_graph.with_ignore(|| {
@@ -296,11 +296,11 @@ impl<'a, 'tcx> InherentCollect<'a, 'tcx> {
             let impl_def_id = self.tcx.hir.local_def_id(item.id);
             let mut rc_vec = self.impls_map.inherent_impls
                                            .entry(def_id)
-                                           .or_insert_with(|| Rc::new(vec![]));
+                                           .or_insert_with(|| Lrc::new(vec![]));
 
             // At this point, there should not be any clones of the
-            // `Rc`, so we can still safely push into it in place:
-            Rc::get_mut(&mut rc_vec).unwrap().push(impl_def_id);
+            // `Lrc`, so we can still safely push into it in place:
+            Lrc::get_mut(&mut rc_vec).unwrap().push(impl_def_id);
         } else {
             struct_span_err!(self.tcx.sess,
                              item.span,
diff --git a/src/librustc_typeck/variance/mod.rs b/src/librustc_typeck/variance/mod.rs
index 418d2b9467096..2392104424355 100644
--- a/src/librustc_typeck/variance/mod.rs
+++ b/src/librustc_typeck/variance/mod.rs
@@ -17,7 +17,7 @@ use rustc::hir;
 use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use rustc::ty::{self, CrateVariancesMap, TyCtxt};
 use rustc::ty::maps::Providers;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 /// Defines the `TermsContext` basically houses an arena where we can
 /// allocate terms.
@@ -44,16 +44,16 @@ pub fn provide(providers: &mut Providers) {
 }
 
 fn crate_variances<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum)
-                             -> Rc<CrateVariancesMap> {
+                             -> Lrc<CrateVariancesMap> {
     assert_eq!(crate_num, LOCAL_CRATE);
     let mut arena = arena::TypedArena::new();
     let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena);
     let constraints_cx = constraints::add_constraints_from_crate(terms_cx);
-    Rc::new(solve::solve_constraints(constraints_cx))
+    Lrc::new(solve::solve_constraints(constraints_cx))
 }
 
 fn variances_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
-                            -> Rc<Vec<ty::Variance>> {
+                            -> Lrc<Vec<ty::Variance>> {
     let id = tcx.hir.as_local_node_id(item_def_id).expect("expected local def-id");
     let unsupported = || {
         // Variance not relevant.
diff --git a/src/librustc_typeck/variance/solve.rs b/src/librustc_typeck/variance/solve.rs
index 434e8ce148f3b..340a7b1d08ede 100644
--- a/src/librustc_typeck/variance/solve.rs
+++ b/src/librustc_typeck/variance/solve.rs
@@ -18,7 +18,7 @@
 use rustc::hir::def_id::DefId;
 use rustc::ty;
 use rustc_data_structures::fx::FxHashMap;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use super::constraints::*;
 use super::terms::*;
@@ -51,7 +51,7 @@ pub fn solve_constraints(constraints_cx: ConstraintContext) -> ty::CrateVariance
     };
     solutions_cx.solve();
     let variances = solutions_cx.create_map();
-    let empty_variance = Rc::new(Vec::new());
+    let empty_variance = Lrc::new(Vec::new());
 
     ty::CrateVariancesMap { variances, empty_variance }
 }
@@ -88,7 +88,7 @@ impl<'a, 'tcx> SolveContext<'a, 'tcx> {
         }
     }
 
-    fn create_map(&self) -> FxHashMap<DefId, Rc<Vec<ty::Variance>>> {
+    fn create_map(&self) -> FxHashMap<DefId, Lrc<Vec<ty::Variance>>> {
         let tcx = self.terms_cx.tcx;
 
         let solutions = &self.solutions;
@@ -109,7 +109,7 @@ impl<'a, 'tcx> SolveContext<'a, 'tcx> {
                 }
             }
 
-            (def_id, Rc::new(variances))
+            (def_id, Lrc::new(variances))
         }).collect()
     }
 
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 914365b003e18..10c30d823d395 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -13,7 +13,7 @@
 use std::collections::BTreeMap;
 use std::io;
 use std::iter::once;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use syntax::ast;
 use rustc::hir;
@@ -403,7 +403,7 @@ fn build_module(cx: &DocContext, did: DefId) -> clean::Module {
 }
 
 struct InlinedConst {
-    nested_bodies: Rc<BTreeMap<hir::BodyId, hir::Body>>
+    nested_bodies: Lrc<BTreeMap<hir::BodyId, hir::Body>>
 }
 
 impl hir::print::PpAnn for InlinedConst {
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index b353c0da865c8..6e48469dc2ecb 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -31,6 +31,7 @@ use errors::emitter::ColorConfig;
 use std::cell::{RefCell, Cell};
 use std::mem;
 use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::path::PathBuf;
 
 use visit_ast::RustdocVisitor;
@@ -134,7 +135,7 @@ pub fn run_core(search_paths: SearchPaths,
         ..config::basic_options().clone()
     };
 
-    let codemap = Rc::new(codemap::CodeMap::new(sessopts.file_path_mapping()));
+    let codemap = Lrc::new(codemap::CodeMap::new(sessopts.file_path_mapping()));
     let diagnostic_handler = errors::Handler::with_tty_emitter(ColorConfig::Auto,
                                                                true,
                                                                false,
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 7ebacdec1f0b2..7aad2b414c925 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -25,6 +25,8 @@
 #![feature(unicode)]
 #![feature(vec_remove_item)]
 
+#![recursion_limit="256"]
+
 extern crate arena;
 extern crate getopts;
 extern crate env_logger;
diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index 8e861f10dd8d4..a9548ee9d8faa 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -18,6 +18,7 @@ use std::panic::{self, AssertUnwindSafe};
 use std::process::Command;
 use std::rc::Rc;
 use std::str;
+use rustc_data_structures::sync::Lrc;
 use std::sync::{Arc, Mutex};
 
 use testing;
@@ -76,7 +77,7 @@ pub fn run(input_path: &Path,
         ..config::basic_options().clone()
     };
 
-    let codemap = Rc::new(CodeMap::new(sessopts.file_path_mapping()));
+    let codemap = Lrc::new(CodeMap::new(sessopts.file_path_mapping()));
     let handler =
         errors::Handler::with_tty_emitter(ColorConfig::Auto,
                                           true, false,
@@ -234,7 +235,7 @@ fn run_test(test: &str, cratename: &str, filename: &FileName, cfgs: Vec<String>,
         }
     }
     let data = Arc::new(Mutex::new(Vec::new()));
-    let codemap = Rc::new(CodeMap::new(sessopts.file_path_mapping()));
+    let codemap = Lrc::new(CodeMap::new(sessopts.file_path_mapping()));
     let emitter = errors::emitter::EmitterWriter::new(box Sink(data.clone()),
                                                       Some(codemap.clone()),
                                                       false);
@@ -449,7 +450,7 @@ pub struct Collector {
     opts: TestOptions,
     maybe_sysroot: Option<PathBuf>,
     position: Span,
-    codemap: Option<Rc<CodeMap>>,
+    codemap: Option<Lrc<CodeMap>>,
     filename: Option<PathBuf>,
     // to be removed when hoedown will be removed as well
     pub render_type: RenderType,
@@ -459,7 +460,7 @@ pub struct Collector {
 impl Collector {
     pub fn new(cratename: String, cfgs: Vec<String>, libs: SearchPaths, externs: Externs,
                use_headers: bool, opts: TestOptions, maybe_sysroot: Option<PathBuf>,
-               codemap: Option<Rc<CodeMap>>, filename: Option<PathBuf>,
+               codemap: Option<Lrc<CodeMap>>, filename: Option<PathBuf>,
                render_type: RenderType, linker: Option<PathBuf>) -> Collector {
         Collector {
             tests: Vec::new(),
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index e0f14c04c6cc9..af8ea29a781cb 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -29,7 +29,7 @@ use tokenstream::{ThinTokenStream, TokenStream};
 use serialize::{self, Encoder, Decoder};
 use std::collections::HashSet;
 use std::fmt;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::u32;
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Copy)]
@@ -1208,7 +1208,7 @@ pub enum LitKind {
     /// A string literal (`"foo"`)
     Str(Symbol, StrStyle),
     /// A byte string (`b"foo"`)
-    ByteStr(Rc<Vec<u8>>),
+    ByteStr(Lrc<Vec<u8>>),
     /// A byte char (`b'f'`)
     Byte(u8),
     /// A character literal (`'a'`)
diff --git a/src/libsyntax/codemap.rs b/src/libsyntax/codemap.rs
index e49a7117192d3..4181f2a6d4a2c 100644
--- a/src/libsyntax/codemap.rs
+++ b/src/libsyntax/codemap.rs
@@ -24,10 +24,9 @@ pub use self::ExpnFormat::*;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::StableHasher;
-use std::cell::{RefCell, Ref};
+use rustc_data_structures::sync::{Lrc, Lock, LockGuard};
 use std::hash::Hash;
 use std::path::{Path, PathBuf};
-use std::rc::Rc;
 
 use std::env;
 use std::fs;
@@ -125,32 +124,32 @@ impl StableFilemapId {
 //
 
 pub struct CodeMap {
-    pub(super) files: RefCell<Vec<Rc<FileMap>>>,
-    file_loader: Box<FileLoader>,
+    pub(super) files: Lock<Vec<Lrc<FileMap>>>,
+    file_loader: Box<FileLoader + Sync + Send>,
     // This is used to apply the file path remapping as specified via
     // -Zremap-path-prefix to all FileMaps allocated within this CodeMap.
     path_mapping: FilePathMapping,
-    stable_id_to_filemap: RefCell<FxHashMap<StableFilemapId, Rc<FileMap>>>,
+    stable_id_to_filemap: Lock<FxHashMap<StableFilemapId, Lrc<FileMap>>>,
 }
 
 impl CodeMap {
     pub fn new(path_mapping: FilePathMapping) -> CodeMap {
         CodeMap {
-            files: RefCell::new(Vec::new()),
+            files: Lock::new(Vec::new()),
             file_loader: Box::new(RealFileLoader),
             path_mapping,
-            stable_id_to_filemap: RefCell::new(FxHashMap()),
+            stable_id_to_filemap: Lock::new(FxHashMap()),
         }
     }
 
-    pub fn with_file_loader(file_loader: Box<FileLoader>,
+    pub fn with_file_loader(file_loader: Box<FileLoader + Sync + Send>,
                             path_mapping: FilePathMapping)
                             -> CodeMap {
         CodeMap {
-            files: RefCell::new(Vec::new()),
-            file_loader,
+            files: Lock::new(Vec::new()),
+            file_loader: file_loader,
             path_mapping,
-            stable_id_to_filemap: RefCell::new(FxHashMap()),
+            stable_id_to_filemap: Lock::new(FxHashMap()),
         }
     }
 
@@ -162,16 +161,16 @@ impl CodeMap {
         self.file_loader.file_exists(path)
     }
 
-    pub fn load_file(&self, path: &Path) -> io::Result<Rc<FileMap>> {
+    pub fn load_file(&self, path: &Path) -> io::Result<Lrc<FileMap>> {
         let src = self.file_loader.read_file(path)?;
         Ok(self.new_filemap(path.to_owned().into(), src))
     }
 
-    pub fn files(&self) -> Ref<Vec<Rc<FileMap>>> {
+    pub fn files(&self) -> LockGuard<Vec<Lrc<FileMap>>> {
         self.files.borrow()
     }
 
-    pub fn filemap_by_stable_id(&self, stable_id: StableFilemapId) -> Option<Rc<FileMap>> {
+    pub fn filemap_by_stable_id(&self, stable_id: StableFilemapId) -> Option<Lrc<FileMap>> {
         self.stable_id_to_filemap.borrow().get(&stable_id).map(|fm| fm.clone())
     }
 
@@ -187,7 +186,7 @@ impl CodeMap {
 
     /// Creates a new filemap without setting its line information. If you don't
     /// intend to set the line information yourself, you should use new_filemap_and_lines.
-    pub fn new_filemap(&self, filename: FileName, src: String) -> Rc<FileMap> {
+    pub fn new_filemap(&self, filename: FileName, src: String) -> Lrc<FileMap> {
         let start_pos = self.next_start_pos();
         let mut files = self.files.borrow_mut();
 
@@ -205,7 +204,7 @@ impl CodeMap {
             },
             other => (other, false),
         };
-        let filemap = Rc::new(FileMap::new(
+        let filemap = Lrc::new(FileMap::new(
             filename,
             was_remapped,
             unmapped_path,
@@ -223,7 +222,7 @@ impl CodeMap {
     }
 
     /// Creates a new filemap and sets its line information.
-    pub fn new_filemap_and_lines(&self, filename: &Path, src: &str) -> Rc<FileMap> {
+    pub fn new_filemap_and_lines(&self, filename: &Path, src: &str) -> Lrc<FileMap> {
         let fm = self.new_filemap(filename.to_owned().into(), src.to_owned());
         let mut byte_pos: u32 = fm.start_pos.0;
         for line in src.lines() {
@@ -251,7 +250,7 @@ impl CodeMap {
                                 mut file_local_lines: Vec<BytePos>,
                                 mut file_local_multibyte_chars: Vec<MultiByteChar>,
                                 mut file_local_non_narrow_chars: Vec<NonNarrowChar>)
-                                -> Rc<FileMap> {
+                                -> Lrc<FileMap> {
         let start_pos = self.next_start_pos();
         let mut files = self.files.borrow_mut();
 
@@ -270,19 +269,19 @@ impl CodeMap {
             *swc = *swc + start_pos;
         }
 
-        let filemap = Rc::new(FileMap {
+        let filemap = Lrc::new(FileMap {
             name: filename,
             name_was_remapped,
             unmapped_path: None,
             crate_of_origin,
             src: None,
             src_hash,
-            external_src: RefCell::new(ExternalSource::AbsentOk),
+            external_src: Lock::new(ExternalSource::AbsentOk),
             start_pos,
             end_pos,
-            lines: RefCell::new(file_local_lines),
-            multibyte_chars: RefCell::new(file_local_multibyte_chars),
-            non_narrow_chars: RefCell::new(file_local_non_narrow_chars),
+            lines: Lock::new(file_local_lines),
+            multibyte_chars: Lock::new(file_local_multibyte_chars),
+            non_narrow_chars: Lock::new(file_local_non_narrow_chars),
             name_hash,
         });
 
@@ -366,7 +365,7 @@ impl CodeMap {
     }
 
     // If the relevant filemap is empty, we don't return a line number.
-    pub fn lookup_line(&self, pos: BytePos) -> Result<FileMapAndLine, Rc<FileMap>> {
+    pub fn lookup_line(&self, pos: BytePos) -> Result<FileMapAndLine, Lrc<FileMap>> {
         let idx = self.lookup_filemap_idx(pos);
 
         let files = self.files.borrow();
@@ -569,7 +568,7 @@ impl CodeMap {
         self.span_until_char(sp, '{')
     }
 
-    pub fn get_filemap(&self, filename: &FileName) -> Option<Rc<FileMap>> {
+    pub fn get_filemap(&self, filename: &FileName) -> Option<Lrc<FileMap>> {
         for fm in self.files.borrow().iter() {
             if *filename == fm.name {
                 return Some(fm.clone());
@@ -666,7 +665,7 @@ impl CodeMapper for CodeMap {
         }
         sp
     }
-    fn ensure_filemap_source_present(&self, file_map: Rc<FileMap>) -> bool {
+    fn ensure_filemap_source_present(&self, file_map: Lrc<FileMap>) -> bool {
         file_map.add_external_src(
             || match file_map.name {
                 FileName::Real(ref name) => self.file_loader.read_file(name).ok(),
@@ -719,7 +718,7 @@ impl FilePathMapping {
 mod tests {
     use super::*;
     use std::borrow::Cow;
-    use std::rc::Rc;
+    use rustc_data_structures::sync::Lrc;
 
     #[test]
     fn t1 () {
@@ -940,7 +939,7 @@ mod tests {
     /// `substring` in `source_text`.
     trait CodeMapExtension {
         fn span_substr(&self,
-                    file: &Rc<FileMap>,
+                    file: &Lrc<FileMap>,
                     source_text: &str,
                     substring: &str,
                     n: usize)
@@ -949,7 +948,7 @@ mod tests {
 
     impl CodeMapExtension for CodeMap {
         fn span_substr(&self,
-                    file: &Rc<FileMap>,
+                    file: &Lrc<FileMap>,
                     source_text: &str,
                     substring: &str,
                     n: usize)
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index d53335f5be7fb..bb61f24026b62 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -28,6 +28,7 @@ use std::collections::HashMap;
 use std::iter;
 use std::path::PathBuf;
 use std::rc::Rc;
+use rustc_data_structures::sync::{Send, Sync, Lrc};
 use std::default::Default;
 use tokenstream::{self, TokenStream};
 
@@ -507,7 +508,6 @@ pub enum MacroKind {
     Derive,
 }
 
-/// An enum representing the different kinds of syntax extensions.
 pub enum SyntaxExtension {
     /// A syntax extension that is attached to an item and creates new items
     /// based upon it.
@@ -515,26 +515,26 @@ pub enum SyntaxExtension {
     /// `#[derive(...)]` is a `MultiItemDecorator`.
     ///
     /// Prefer ProcMacro or MultiModifier since they are more flexible.
-    MultiDecorator(Box<MultiItemDecorator>),
+    MultiDecorator(Box<MultiItemDecorator + Sync + Send>),
 
     /// A syntax extension that is attached to an item and modifies it
     /// in-place. Also allows decoration, i.e., creating new items.
-    MultiModifier(Box<MultiItemModifier>),
+    MultiModifier(Box<MultiItemModifier + Sync + Send>),
 
     /// A function-like procedural macro. TokenStream -> TokenStream.
-    ProcMacro(Box<ProcMacro>),
+    ProcMacro(Box<ProcMacro + Sync + Send>),
 
     /// An attribute-like procedural macro. TokenStream, TokenStream -> TokenStream.
     /// The first TokenSteam is the attribute, the second is the annotated item.
     /// Allows modification of the input items and adding new items, similar to
     /// MultiModifier, but uses TokenStreams, rather than AST nodes.
-    AttrProcMacro(Box<AttrProcMacro>),
+    AttrProcMacro(Box<AttrProcMacro + Sync + Send>),
 
     /// A normal, function-like syntax extension.
     ///
     /// `bytes!` is a `NormalTT`.
     NormalTT {
-        expander: Box<TTMacroExpander>,
+        expander: Box<TTMacroExpander + Sync + Send>,
         def_info: Option<(ast::NodeId, Span)>,
         /// Whether the contents of the macro can
         /// directly use `#[unstable]` things (true == yes).
@@ -547,13 +547,13 @@ pub enum SyntaxExtension {
     /// A function-like syntax extension that has an extra ident before
     /// the block.
     ///
-    IdentTT(Box<IdentMacroExpander>, Option<Span>, bool),
+    IdentTT(Box<IdentMacroExpander + Sync + Send>, Option<Span>, bool),
 
     /// An attribute-like procedural macro. TokenStream -> TokenStream.
     /// The input is the annotated item.
     /// Allows generating code to implement a Trait for a given struct
     /// or enum item.
-    ProcMacroDerive(Box<MultiItemModifier>, Vec<Symbol> /* inert attribute names */),
+    ProcMacroDerive(Box<MultiItemModifier + Sync + Send>, Vec<Symbol> /* inert attribute names */),
 
     /// An attribute-like procedural macro that derives a builtin trait.
     BuiltinDerive(BuiltinDeriveFn),
@@ -561,7 +561,7 @@ pub enum SyntaxExtension {
     /// A declarative macro, e.g. `macro m() {}`.
     ///
     /// The second element is the definition site span.
-    DeclMacro(Box<TTMacroExpander>, Option<(ast::NodeId, Span)>),
+    DeclMacro(Box<TTMacroExpander + Sync + Send>, Option<(ast::NodeId, Span)>),
 }
 
 impl SyntaxExtension {
@@ -603,15 +603,15 @@ pub trait Resolver {
     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool;
 
     fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion, derives: &[Mark]);
-    fn add_builtin(&mut self, ident: ast::Ident, ext: Rc<SyntaxExtension>);
+    fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>);
 
     fn resolve_imports(&mut self);
     // Resolves attribute and derive legacy macros from `#![plugin(..)]`.
     fn find_legacy_attr_invoc(&mut self, attrs: &mut Vec<Attribute>) -> Option<Attribute>;
     fn resolve_invoc(&mut self, invoc: &mut Invocation, scope: Mark, force: bool)
-                     -> Result<Option<Rc<SyntaxExtension>>, Determinacy>;
+                     -> Result<Option<Lrc<SyntaxExtension>>, Determinacy>;
     fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
-                     -> Result<Rc<SyntaxExtension>, Determinacy>;
+                     -> Result<Lrc<SyntaxExtension>, Determinacy>;
     fn check_unused_macros(&self);
 }
 
@@ -630,16 +630,16 @@ impl Resolver for DummyResolver {
     fn is_whitelisted_legacy_custom_derive(&self, _name: Name) -> bool { false }
 
     fn visit_expansion(&mut self, _invoc: Mark, _expansion: &Expansion, _derives: &[Mark]) {}
-    fn add_builtin(&mut self, _ident: ast::Ident, _ext: Rc<SyntaxExtension>) {}
+    fn add_builtin(&mut self, _ident: ast::Ident, _ext: Lrc<SyntaxExtension>) {}
 
     fn resolve_imports(&mut self) {}
     fn find_legacy_attr_invoc(&mut self, _attrs: &mut Vec<Attribute>) -> Option<Attribute> { None }
     fn resolve_invoc(&mut self, _invoc: &mut Invocation, _scope: Mark, _force: bool)
-                     -> Result<Option<Rc<SyntaxExtension>>, Determinacy> {
+                     -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
         Err(Determinacy::Determined)
     }
     fn resolve_macro(&mut self, _scope: Mark, _path: &ast::Path, _kind: MacroKind,
-                     _force: bool) -> Result<Rc<SyntaxExtension>, Determinacy> {
+                     _force: bool) -> Result<Lrc<SyntaxExtension>, Determinacy> {
         Err(Determinacy::Determined)
     }
     fn check_unused_macros(&self) {}
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 81baa0c3954ca..fc4624ba3bb0b 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -39,6 +39,7 @@ use std::io::Read;
 use std::mem;
 use std::rc::Rc;
 use std::path::PathBuf;
+use rustc_data_structures::sync::Lrc;
 
 macro_rules! expansions {
     ($($kind:ident: $ty:ty [$($vec:ident, $ty_elt:ty)*], $kind_name:expr, .$make:ident,
@@ -446,7 +447,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         }
     }
 
-    fn expand_invoc(&mut self, invoc: Invocation, ext: Rc<SyntaxExtension>) -> Expansion {
+    fn expand_invoc(&mut self, invoc: Invocation, ext: Lrc<SyntaxExtension>) -> Expansion {
         let result = match invoc.kind {
             InvocationKind::Bang { .. } => self.expand_bang_invoc(invoc, ext),
             InvocationKind::Attr { .. } => self.expand_attr_invoc(invoc, ext),
@@ -470,7 +471,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         result
     }
 
-    fn expand_attr_invoc(&mut self, invoc: Invocation, ext: Rc<SyntaxExtension>) -> Expansion {
+    fn expand_attr_invoc(&mut self, invoc: Invocation, ext: Lrc<SyntaxExtension>) -> Expansion {
         let Invocation { expansion_kind: kind, .. } = invoc;
         let (attr, item) = match invoc.kind {
             InvocationKind::Attr { attr, item, .. } => (attr.unwrap(), item),
@@ -525,7 +526,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     }
 
     /// Expand a macro invocation. Returns the result of expansion.
-    fn expand_bang_invoc(&mut self, invoc: Invocation, ext: Rc<SyntaxExtension>) -> Expansion {
+    fn expand_bang_invoc(&mut self, invoc: Invocation, ext: Lrc<SyntaxExtension>) -> Expansion {
         let (mark, kind) = (invoc.expansion_data.mark, invoc.expansion_kind);
         let (mac, ident, span) = match invoc.kind {
             InvocationKind::Bang { mac, ident, span } => (mac, ident, span),
@@ -651,7 +652,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     }
 
     /// Expand a derive invocation. Returns the result of expansion.
-    fn expand_derive_invoc(&mut self, invoc: Invocation, ext: Rc<SyntaxExtension>) -> Expansion {
+    fn expand_derive_invoc(&mut self, invoc: Invocation, ext: Lrc<SyntaxExtension>) -> Expansion {
         let Invocation { expansion_kind: kind, .. } = invoc;
         let (path, item) = match invoc.kind {
             InvocationKind::Derive { path, item } => (path, item),
diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 4da485fc9a42c..42552cc1407ba 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -24,7 +24,7 @@ use util::small_vector::SmallVector;
 use std::fs::File;
 use std::io::prelude::*;
 use std::path::PathBuf;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 // These macros all relate to the file system; they either return
 // the column/row/filename of the expression, or they include
@@ -183,7 +183,7 @@ pub fn expand_include_bytes(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::Toke
             // dependency information, but don't enter it's contents
             cx.codemap().new_filemap_and_lines(&file, "");
 
-            base::MacEager::expr(cx.expr_lit(sp, ast::LitKind::ByteStr(Rc::new(bytes))))
+            base::MacEager::expr(cx.expr_lit(sp, ast::LitKind::ByteStr(Lrc::new(bytes))))
         }
     }
 }
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 5e58f003c2be7..823ca1b025de8 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use rustc_data_structures::sync::RwLock;
+
 use {ast, attr};
 use syntax_pos::{Span, DUMMY_SP};
 use ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension};
@@ -26,10 +28,10 @@ use parse::token::Token::*;
 use symbol::Symbol;
 use tokenstream::{TokenStream, TokenTree};
 
-use std::cell::RefCell;
 use std::collections::HashMap;
 use std::collections::hash_map::Entry;
-use std::rc::Rc;
+
+use rustc_data_structures::sync::Lrc;
 
 pub struct ParserAnyMacro<'a> {
     parser: Parser<'a>,
@@ -183,7 +185,7 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
 // Holy self-referential!
 
 /// Converts a `macro_rules!` invocation into a syntax extension.
-pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item) -> SyntaxExtension {
+pub fn compile(sess: &ParseSess, features: &RwLock<Features>, def: &ast::Item) -> SyntaxExtension {
     let lhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("lhs"));
     let rhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("rhs"));
 
@@ -199,7 +201,7 @@ pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item)
     // ...quasiquoting this would be nice.
     // These spans won't matter, anyways
     let argument_gram = vec![
-        quoted::TokenTree::Sequence(DUMMY_SP, Rc::new(quoted::SequenceRepetition {
+        quoted::TokenTree::Sequence(DUMMY_SP, Lrc::new(quoted::SequenceRepetition {
             tts: vec![
                 quoted::TokenTree::MetaVarDecl(DUMMY_SP, lhs_nm, ast::Ident::from_str("tt")),
                 quoted::TokenTree::Token(DUMMY_SP, token::FatArrow),
@@ -210,7 +212,7 @@ pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item)
             num_captures: 2,
         })),
         // to phase into semicolon-termination instead of semicolon-separation
-        quoted::TokenTree::Sequence(DUMMY_SP, Rc::new(quoted::SequenceRepetition {
+        quoted::TokenTree::Sequence(DUMMY_SP, Lrc::new(quoted::SequenceRepetition {
             tts: vec![quoted::TokenTree::Token(DUMMY_SP, token::Semi)],
             separator: None,
             op: quoted::KleeneOp::ZeroOrMore,
@@ -293,7 +295,7 @@ pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item)
 }
 
 fn check_lhs_nt_follows(sess: &ParseSess,
-                        features: &RefCell<Features>,
+                        features: &RwLock<Features>,
                         attrs: &[ast::Attribute],
                         lhs: &quoted::TokenTree) -> bool {
     // lhs is going to be like TokenTree::Delimited(...), where the
@@ -350,7 +352,7 @@ fn check_rhs(sess: &ParseSess, rhs: &quoted::TokenTree) -> bool {
 }
 
 fn check_matcher(sess: &ParseSess,
-                 features: &RefCell<Features>,
+                 features: &RwLock<Features>,
                  attrs: &[ast::Attribute],
                  matcher: &[quoted::TokenTree]) -> bool {
     let first_sets = FirstSets::new(matcher);
@@ -598,7 +600,7 @@ impl TokenSet {
 // Requires that `first_sets` is pre-computed for `matcher`;
 // see `FirstSets::new`.
 fn check_matcher_core(sess: &ParseSess,
-                      features: &RefCell<Features>,
+                      features: &RwLock<Features>,
                       attrs: &[ast::Attribute],
                       first_sets: &FirstSets,
                       matcher: &[quoted::TokenTree],
@@ -865,7 +867,7 @@ fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> Result<bool, (String, &'
 }
 
 fn has_legal_fragment_specifier(sess: &ParseSess,
-                                features: &RefCell<Features>,
+                                features: &RwLock<Features>,
                                 attrs: &[ast::Attribute],
                                 tok: &quoted::TokenTree) -> Result<(), String> {
     debug!("has_legal_fragment_specifier({:?})", tok);
@@ -880,7 +882,7 @@ fn has_legal_fragment_specifier(sess: &ParseSess,
 }
 
 fn is_legal_fragment_specifier(sess: &ParseSess,
-                               features: &RefCell<Features>,
+                               features: &RwLock<Features>,
                                attrs: &[ast::Attribute],
                                frag_name: &str,
                                frag_span: Span) -> bool {
diff --git a/src/libsyntax/ext/tt/quoted.rs b/src/libsyntax/ext/tt/quoted.rs
index 0e21e3f6b0010..1a9cee768c340 100644
--- a/src/libsyntax/ext/tt/quoted.rs
+++ b/src/libsyntax/ext/tt/quoted.rs
@@ -16,7 +16,7 @@ use symbol::keywords;
 use syntax_pos::{DUMMY_SP, Span, BytePos};
 use tokenstream;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct Delimited {
@@ -77,9 +77,9 @@ pub enum KleeneOp {
 #[derive(Debug, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
 pub enum TokenTree {
     Token(Span, token::Token),
-    Delimited(Span, Rc<Delimited>),
+    Delimited(Span, Lrc<Delimited>),
     /// A kleene-style repetition sequence
-    Sequence(Span, Rc<SequenceRepetition>),
+    Sequence(Span, Lrc<SequenceRepetition>),
     /// E.g. `$var`
     MetaVar(Span, ast::Ident),
     /// E.g. `$var:expr`. This is only used in the left hand side of MBE macros.
@@ -189,7 +189,7 @@ fn parse_tree<I>(tree: tokenstream::TokenTree,
                 let sequence = parse(delimited.tts.into(), expect_matchers, sess);
                 let (separator, op) = parse_sep_and_kleene_op(trees, span, sess);
                 let name_captures = macro_parser::count_names(&sequence);
-                TokenTree::Sequence(span, Rc::new(SequenceRepetition {
+                TokenTree::Sequence(span, Lrc::new(SequenceRepetition {
                     tts: sequence,
                     separator,
                     op,
@@ -215,7 +215,7 @@ fn parse_tree<I>(tree: tokenstream::TokenTree,
         },
         tokenstream::TokenTree::Token(span, tok) => TokenTree::Token(span, tok),
         tokenstream::TokenTree::Delimited(span, delimited) => {
-            TokenTree::Delimited(span, Rc::new(Delimited {
+            TokenTree::Delimited(span, Lrc::new(Delimited {
                 delim: delimited.delim,
                 tts: parse(delimited.tts.into(), expect_matchers, sess),
             }))
diff --git a/src/libsyntax/ext/tt/transcribe.rs b/src/libsyntax/ext/tt/transcribe.rs
index d51b0d0ae3e93..7883c4bbc1648 100644
--- a/src/libsyntax/ext/tt/transcribe.rs
+++ b/src/libsyntax/ext/tt/transcribe.rs
@@ -20,6 +20,7 @@ use tokenstream::{TokenStream, TokenTree, Delimited};
 use util::small_vector::SmallVector;
 
 use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::mem;
 use std::ops::Add;
 use std::collections::HashMap;
@@ -27,12 +28,12 @@ use std::collections::HashMap;
 // An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
 enum Frame {
     Delimited {
-        forest: Rc<quoted::Delimited>,
+        forest: Lrc<quoted::Delimited>,
         idx: usize,
         span: Span,
     },
     Sequence {
-        forest: Rc<quoted::SequenceRepetition>,
+        forest: Lrc<quoted::SequenceRepetition>,
         idx: usize,
         sep: Option<Token>,
     },
@@ -40,7 +41,7 @@ enum Frame {
 
 impl Frame {
     fn new(tts: Vec<quoted::TokenTree>) -> Frame {
-        let forest = Rc::new(quoted::Delimited { delim: token::NoDelim, tts: tts });
+        let forest = Lrc::new(quoted::Delimited { delim: token::NoDelim, tts: tts });
         Frame::Delimited { forest: forest, idx: 0, span: DUMMY_SP }
     }
 }
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 9916b74aeb315..25841578e6297 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -29,7 +29,7 @@ use tokenstream::*;
 use util::small_vector::SmallVector;
 use util::move_map::MoveMap;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 pub trait Folder : Sized {
     // Any additions to this trait should happen in form
@@ -577,7 +577,7 @@ pub fn noop_fold_token<T: Folder>(t: token::Token, fld: &mut T) -> token::Token
         token::Ident(id) => token::Ident(fld.fold_ident(id)),
         token::Lifetime(id) => token::Lifetime(fld.fold_ident(id)),
         token::Interpolated(nt) => {
-            let nt = match Rc::try_unwrap(nt) {
+            let nt = match Lrc::try_unwrap(nt) {
                 Ok(nt) => nt,
                 Err(nt) => (*nt).clone(),
             };
diff --git a/src/libsyntax/json.rs b/src/libsyntax/json.rs
index 54c726d84621f..a31439632cad4 100644
--- a/src/libsyntax/json.rs
+++ b/src/libsyntax/json.rs
@@ -26,7 +26,7 @@ use errors::{DiagnosticBuilder, SubDiagnostic, CodeSuggestion, CodeMapper};
 use errors::DiagnosticId;
 use errors::emitter::{Emitter, EmitterWriter};
 
-use std::rc::Rc;
+use rustc_data_structures::sync::{self, Sync, Lrc};
 use std::io::{self, Write};
 use std::vec;
 use std::sync::{Arc, Mutex};
@@ -36,13 +36,13 @@ use rustc_serialize::json::{as_json, as_pretty_json};
 pub struct JsonEmitter {
     dst: Box<Write + Send>,
     registry: Option<Registry>,
-    cm: Rc<CodeMapper + 'static>,
+    cm: Lrc<CodeMapper + sync::Send + Sync>,
     pretty: bool,
 }
 
 impl JsonEmitter {
     pub fn stderr(registry: Option<Registry>,
-                  code_map: Rc<CodeMap>,
+                  code_map: Lrc<CodeMap>,
                   pretty: bool) -> JsonEmitter {
         JsonEmitter {
             dst: Box::new(io::stderr()),
@@ -54,12 +54,12 @@ impl JsonEmitter {
 
     pub fn basic(pretty: bool) -> JsonEmitter {
         let file_path_mapping = FilePathMapping::empty();
-        JsonEmitter::stderr(None, Rc::new(CodeMap::new(file_path_mapping)), pretty)
+        JsonEmitter::stderr(None, Lrc::new(CodeMap::new(file_path_mapping)), pretty)
     }
 
     pub fn new(dst: Box<Write + Send>,
                registry: Option<Registry>,
-               code_map: Rc<CodeMap>,
+               code_map: Lrc<CodeMap>,
                pretty: bool) -> JsonEmitter {
         JsonEmitter {
             dst,
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 0b51f2e981456..350f84359f2e5 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -26,6 +26,8 @@
 #![feature(i128_type)]
 #![feature(const_atomic_usize_new)]
 
+#![recursion_limit="256"]
+
 // See librustc_cratesio_shim/Cargo.toml for a comment explaining this.
 #[allow(unused_extern_crates)]
 extern crate rustc_cratesio_shim;
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 9828995362a35..6839be9e77595 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -20,7 +20,7 @@ use std_unicode::property::Pattern_White_Space;
 use std::borrow::Cow;
 use std::char;
 use std::mem::replace;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 pub mod comments;
 mod tokentrees;
@@ -48,7 +48,7 @@ pub struct StringReader<'a> {
     pub col: CharPos,
     /// The current character (which has been read from self.pos)
     pub ch: Option<char>,
-    pub filemap: Rc<syntax_pos::FileMap>,
+    pub filemap: Lrc<syntax_pos::FileMap>,
     /// If Some, stop reading the source at this position (inclusive).
     pub terminator: Option<BytePos>,
     /// Whether to record new-lines and multibyte chars in filemap.
@@ -61,7 +61,7 @@ pub struct StringReader<'a> {
     pub fatal_errs: Vec<DiagnosticBuilder<'a>>,
     // cache a direct reference to the source text, so that we don't have to
     // retrieve it via `self.filemap.src.as_ref().unwrap()` all the time.
-    source_text: Rc<String>,
+    source_text: Lrc<String>,
     /// Stack of open delimiters and their spans. Used for error message.
     token: token::Token,
     span: Span,
@@ -152,13 +152,13 @@ impl<'a> StringReader<'a> {
 
 impl<'a> StringReader<'a> {
     /// For comments.rs, which hackily pokes into next_pos and ch
-    pub fn new_raw(sess: &'a ParseSess, filemap: Rc<syntax_pos::FileMap>) -> Self {
+    pub fn new_raw(sess: &'a ParseSess, filemap: Lrc<syntax_pos::FileMap>) -> Self {
         let mut sr = StringReader::new_raw_internal(sess, filemap);
         sr.bump();
         sr
     }
 
-    fn new_raw_internal(sess: &'a ParseSess, filemap: Rc<syntax_pos::FileMap>) -> Self {
+    fn new_raw_internal(sess: &'a ParseSess, filemap: Lrc<syntax_pos::FileMap>) -> Self {
         if filemap.src.is_none() {
             sess.span_diagnostic.bug(&format!("Cannot lex filemap without source: {}",
                                               filemap.name));
@@ -187,7 +187,7 @@ impl<'a> StringReader<'a> {
         }
     }
 
-    pub fn new(sess: &'a ParseSess, filemap: Rc<syntax_pos::FileMap>) -> Self {
+    pub fn new(sess: &'a ParseSess, filemap: Lrc<syntax_pos::FileMap>) -> Self {
         let mut sr = StringReader::new_raw(sess, filemap);
         if sr.advance_token().is_err() {
             sr.emit_fatal_errors();
@@ -1737,13 +1737,11 @@ mod tests {
     use errors;
     use feature_gate::UnstableFeatures;
     use parse::token;
-    use std::cell::RefCell;
     use std::collections::HashSet;
     use std::io;
     use std::path::PathBuf;
-    use std::rc::Rc;
-
-    fn mk_sess(cm: Rc<CodeMap>) -> ParseSess {
+    use rustc_data_structures::sync::{Lrc, Lock};
+    fn mk_sess(cm: Lrc<CodeMap>) -> ParseSess {
         let emitter = errors::emitter::EmitterWriter::new(Box::new(io::sink()),
                                                           Some(cm.clone()),
                                                           false);
@@ -1751,10 +1749,10 @@ mod tests {
             span_diagnostic: errors::Handler::with_emitter(true, false, Box::new(emitter)),
             unstable_features: UnstableFeatures::from_environment(),
             config: CrateConfig::new(),
-            included_mod_stack: RefCell::new(Vec::new()),
+            included_mod_stack: Lock::new(Vec::new()),
             code_map: cm,
-            missing_fragment_specifiers: RefCell::new(HashSet::new()),
-            non_modrs_mods: RefCell::new(vec![]),
+            missing_fragment_specifiers: Lock::new(HashSet::new()),
+            non_modrs_mods: Lock::new(vec![]),
         }
     }
 
@@ -1769,7 +1767,7 @@ mod tests {
 
     #[test]
     fn t1() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         let mut string_reader = setup(&cm,
                                       &sh,
@@ -1813,7 +1811,7 @@ mod tests {
 
     #[test]
     fn doublecolonparsing() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         check_tokenization(setup(&cm, &sh, "a b".to_string()),
                            vec![mk_ident("a"), token::Whitespace, mk_ident("b")]);
@@ -1821,7 +1819,7 @@ mod tests {
 
     #[test]
     fn dcparsing_2() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         check_tokenization(setup(&cm, &sh, "a::b".to_string()),
                            vec![mk_ident("a"), token::ModSep, mk_ident("b")]);
@@ -1829,7 +1827,7 @@ mod tests {
 
     #[test]
     fn dcparsing_3() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         check_tokenization(setup(&cm, &sh, "a ::b".to_string()),
                            vec![mk_ident("a"), token::Whitespace, token::ModSep, mk_ident("b")]);
@@ -1837,7 +1835,7 @@ mod tests {
 
     #[test]
     fn dcparsing_4() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         check_tokenization(setup(&cm, &sh, "a:: b".to_string()),
                            vec![mk_ident("a"), token::ModSep, token::Whitespace, mk_ident("b")]);
@@ -1845,7 +1843,7 @@ mod tests {
 
     #[test]
     fn character_a() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         assert_eq!(setup(&cm, &sh, "'a'".to_string()).next_token().tok,
                    token::Literal(token::Char(Symbol::intern("a")), None));
@@ -1853,7 +1851,7 @@ mod tests {
 
     #[test]
     fn character_space() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         assert_eq!(setup(&cm, &sh, "' '".to_string()).next_token().tok,
                    token::Literal(token::Char(Symbol::intern(" ")), None));
@@ -1861,7 +1859,7 @@ mod tests {
 
     #[test]
     fn character_escaped() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         assert_eq!(setup(&cm, &sh, "'\\n'".to_string()).next_token().tok,
                    token::Literal(token::Char(Symbol::intern("\\n")), None));
@@ -1869,7 +1867,7 @@ mod tests {
 
     #[test]
     fn lifetime_name() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         assert_eq!(setup(&cm, &sh, "'abc".to_string()).next_token().tok,
                    token::Lifetime(Ident::from_str("'abc")));
@@ -1877,7 +1875,7 @@ mod tests {
 
     #[test]
     fn raw_string() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         assert_eq!(setup(&cm, &sh, "r###\"\"#a\\b\x00c\"\"###".to_string())
                        .next_token()
@@ -1887,7 +1885,7 @@ mod tests {
 
     #[test]
     fn literal_suffixes() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         macro_rules! test {
             ($input: expr, $tok_type: ident, $tok_contents: expr) => {{
@@ -1931,7 +1929,7 @@ mod tests {
 
     #[test]
     fn nested_block_comments() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         let mut lexer = setup(&cm, &sh, "/* /* */ */'a'".to_string());
         match lexer.next_token().tok {
@@ -1944,7 +1942,7 @@ mod tests {
 
     #[test]
     fn crlf_comments() {
-        let cm = Rc::new(CodeMap::new(FilePathMapping::empty()));
+        let cm = Lrc::new(CodeMap::new(FilePathMapping::empty()));
         let sh = mk_sess(cm.clone());
         let mut lexer = setup(&cm, &sh, "// test\r\n/// test\r\n".to_string());
         let comment = lexer.next_token();
diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index a38ceba2f45a9..52fb6e128f08a 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -10,6 +10,7 @@
 
 //! The main parser interface
 
+use rustc_data_structures::sync::{Lrc, Lock};
 use ast::{self, CrateConfig};
 use codemap::{CodeMap, FilePathMapping};
 use syntax_pos::{self, Span, FileMap, NO_EXPANSION, FileName};
@@ -21,11 +22,9 @@ use str::char_at;
 use symbol::Symbol;
 use tokenstream::{TokenStream, TokenTree};
 
-use std::cell::RefCell;
 use std::collections::HashSet;
 use std::iter;
 use std::path::{Path, PathBuf};
-use std::rc::Rc;
 use std::str;
 
 pub type PResult<'a, T> = Result<T, DiagnosticBuilder<'a>>;
@@ -46,18 +45,18 @@ pub struct ParseSess {
     pub span_diagnostic: Handler,
     pub unstable_features: UnstableFeatures,
     pub config: CrateConfig,
-    pub missing_fragment_specifiers: RefCell<HashSet<Span>>,
+    pub missing_fragment_specifiers: Lock<HashSet<Span>>,
     // Spans where a `mod foo;` statement was included in a non-mod.rs file.
     // These are used to issue errors if the non_modrs_mods feature is not enabled.
-    pub non_modrs_mods: RefCell<Vec<(ast::Ident, Span)>>,
+    pub non_modrs_mods: Lock<Vec<(ast::Ident, Span)>>,
     /// Used to determine and report recursive mod inclusions
-    included_mod_stack: RefCell<Vec<PathBuf>>,
-    code_map: Rc<CodeMap>,
+    included_mod_stack: Lock<Vec<PathBuf>>,
+    code_map: Lrc<CodeMap>,
 }
 
 impl ParseSess {
     pub fn new(file_path_mapping: FilePathMapping) -> Self {
-        let cm = Rc::new(CodeMap::new(file_path_mapping));
+        let cm = Lrc::new(CodeMap::new(file_path_mapping));
         let handler = Handler::with_tty_emitter(ColorConfig::Auto,
                                                 true,
                                                 false,
@@ -65,15 +64,15 @@ impl ParseSess {
         ParseSess::with_span_handler(handler, cm)
     }
 
-    pub fn with_span_handler(handler: Handler, code_map: Rc<CodeMap>) -> ParseSess {
+    pub fn with_span_handler(handler: Handler, code_map: Lrc<CodeMap>) -> ParseSess {
         ParseSess {
             span_diagnostic: handler,
             unstable_features: UnstableFeatures::from_environment(),
             config: HashSet::new(),
-            missing_fragment_specifiers: RefCell::new(HashSet::new()),
-            included_mod_stack: RefCell::new(vec![]),
+            missing_fragment_specifiers: Lock::new(HashSet::new()),
+            included_mod_stack: Lock::new(vec![]),
             code_map,
-            non_modrs_mods: RefCell::new(vec![]),
+            non_modrs_mods: Lock::new(vec![]),
         }
     }
 
@@ -183,7 +182,7 @@ pub fn new_sub_parser_from_file<'a>(sess: &'a ParseSess,
 }
 
 /// Given a filemap and config, return a parser
-pub fn filemap_to_parser(sess: & ParseSess, filemap: Rc<FileMap>, ) -> Parser {
+pub fn filemap_to_parser(sess: & ParseSess, filemap: Lrc<FileMap>) -> Parser {
     let end_pos = filemap.end_pos;
     let mut parser = stream_to_parser(sess, filemap_to_stream(sess, filemap, None));
 
@@ -206,7 +205,7 @@ pub fn new_parser_from_tts(sess: &ParseSess, tts: Vec<TokenTree>) -> Parser {
 /// Given a session and a path and an optional span (for error reporting),
 /// add the path to the session's codemap and return the new filemap.
 fn file_to_filemap(sess: &ParseSess, path: &Path, spanopt: Option<Span>)
-                   -> Rc<FileMap> {
+                   -> Lrc<FileMap> {
     match sess.codemap().load_file(path) {
         Ok(filemap) => filemap,
         Err(e) => {
@@ -220,7 +219,7 @@ fn file_to_filemap(sess: &ParseSess, path: &Path, spanopt: Option<Span>)
 }
 
 /// Given a filemap, produce a sequence of token-trees
-pub fn filemap_to_stream(sess: &ParseSess, filemap: Rc<FileMap>, override_span: Option<Span>)
+pub fn filemap_to_stream(sess: &ParseSess, filemap: Lrc<FileMap>, override_span: Option<Span>)
                          -> TokenStream {
     let mut srdr = lexer::StringReader::new(sess, filemap);
     srdr.override_span = override_span;
@@ -422,7 +421,7 @@ pub fn lit_token(lit: token::Lit, suf: Option<Symbol>, diag: Option<(Span, &Hand
             (true, Some(LitKind::ByteStr(byte_str_lit(&i.as_str()))))
         }
         token::ByteStrRaw(i, _) => {
-            (true, Some(LitKind::ByteStr(Rc::new(i.to_string().into_bytes()))))
+            (true, Some(LitKind::ByteStr(Lrc::new(i.to_string().into_bytes()))))
         }
     }
 }
@@ -496,7 +495,7 @@ pub fn byte_lit(lit: &str) -> (u8, usize) {
     }
 }
 
-pub fn byte_str_lit(lit: &str) -> Rc<Vec<u8>> {
+pub fn byte_str_lit(lit: &str) -> Lrc<Vec<u8>> {
     let mut res = Vec::with_capacity(lit.len());
 
     // FIXME #8372: This could be a for-loop if it didn't borrow the iterator
@@ -553,7 +552,7 @@ pub fn byte_str_lit(lit: &str) -> Rc<Vec<u8>> {
         }
     }
 
-    Rc::new(res)
+    Lrc::new(res)
 }
 
 pub fn integer_lit(s: &str, suffix: Option<Symbol>, diag: Option<(Span, &Handler)>)
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 05368c52d2c32..3405549b36763 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -25,9 +25,8 @@ use syntax_pos::{self, Span, FileName};
 use tokenstream::{TokenStream, TokenTree};
 use tokenstream;
 
-use std::cell::Cell;
 use std::{cmp, fmt};
-use std::rc::Rc;
+use rustc_data_structures::sync::{Lrc, LockCell};
 
 #[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Hash, Debug, Copy)]
 pub enum BinOpToken {
@@ -179,7 +178,7 @@ pub enum Token {
 
     // The `LazyTokenStream` is a pure function of the `Nonterminal`,
     // and so the `LazyTokenStream` can be ignored by Eq, Hash, etc.
-    Interpolated(Rc<(Nonterminal, LazyTokenStream)>),
+    Interpolated(Lrc<(Nonterminal, LazyTokenStream)>),
     // Can be expanded into several tokens.
     /// Doc comment
     DocComment(ast::Name),
@@ -199,7 +198,7 @@ pub enum Token {
 
 impl Token {
     pub fn interpolated(nt: Nonterminal) -> Token {
-        Token::Interpolated(Rc::new((nt, LazyTokenStream::new())))
+        Token::Interpolated(Lrc::new((nt, LazyTokenStream::new())))
     }
 
     /// Returns `true` if the token starts with '>'.
@@ -559,13 +558,13 @@ pub fn is_op(tok: &Token) -> bool {
     }
 }
 
-pub struct LazyTokenStream(Cell<Option<TokenStream>>);
+pub struct LazyTokenStream(LockCell<Option<TokenStream>>);
 
 impl Clone for LazyTokenStream {
     fn clone(&self) -> Self {
         let opt_stream = self.0.take();
         self.0.set(opt_stream.clone());
-        LazyTokenStream(Cell::new(opt_stream))
+        LazyTokenStream(LockCell::new(opt_stream))
     }
 }
 
@@ -584,7 +583,7 @@ impl fmt::Debug for LazyTokenStream {
 
 impl LazyTokenStream {
     pub fn new() -> Self {
-        LazyTokenStream(Cell::new(None))
+        LazyTokenStream(LockCell::new(None))
     }
 
     pub fn force<F: FnOnce() -> TokenStream>(&self, f: F) -> TokenStream {
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index 1a0f4e9278da6..adb8f8569eb18 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -21,7 +21,6 @@ use std::mem;
 use std::vec;
 use attr::{self, HasAttrs};
 use syntax_pos::{self, DUMMY_SP, NO_EXPANSION, Span, FileMap, BytePos};
-use std::rc::Rc;
 
 use codemap::{self, CodeMap, ExpnInfo, NameAndSpan, MacroAttribute, dummy_spanned};
 use errors;
diff --git a/src/libsyntax/test_snippet.rs b/src/libsyntax/test_snippet.rs
index 5072f2e2793f1..21053145d9bb9 100644
--- a/src/libsyntax/test_snippet.rs
+++ b/src/libsyntax/test_snippet.rs
@@ -13,7 +13,7 @@ use errors::Handler;
 use errors::emitter::EmitterWriter;
 use std::io;
 use std::io::prelude::*;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::str;
 use std::sync::{Arc, Mutex};
 use std::path::Path;
@@ -48,7 +48,7 @@ impl<T: Write> Write for Shared<T> {
 fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &str) {
     let output = Arc::new(Mutex::new(Vec::new()));
 
-    let code_map = Rc::new(CodeMap::new(FilePathMapping::empty()));
+    let code_map = Lrc::new(CodeMap::new(FilePathMapping::empty()));
     code_map.new_filemap_and_lines(Path::new("test.rs"), &file_text);
 
     let primary_span = make_span(&file_text, &span_labels[0].start, &span_labels[0].end);
diff --git a/src/libsyntax/util/rc_slice.rs b/src/libsyntax/util/rc_slice.rs
index d6939d71129e4..520b7a48e3025 100644
--- a/src/libsyntax/util/rc_slice.rs
+++ b/src/libsyntax/util/rc_slice.rs
@@ -10,14 +10,14 @@
 
 use std::fmt;
 use std::ops::{Deref, Range};
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
                                            HashStable};
 
 #[derive(Clone)]
 pub struct RcSlice<T> {
-    data: Rc<Box<[T]>>,
+    data: Lrc<Box<[T]>>,
     offset: u32,
     len: u32,
 }
@@ -27,7 +27,7 @@ impl<T> RcSlice<T> {
         RcSlice {
             offset: 0,
             len: vec.len() as u32,
-            data: Rc::new(vec.into_boxed_slice()),
+            data: Lrc::new(vec.into_boxed_slice()),
         }
     }
 
diff --git a/src/libsyntax_ext/Cargo.toml b/src/libsyntax_ext/Cargo.toml
index 1c4702402886d..d8eeb5ed2554a 100644
--- a/src/libsyntax_ext/Cargo.toml
+++ b/src/libsyntax_ext/Cargo.toml
@@ -14,3 +14,4 @@ proc_macro = { path = "../libproc_macro" }
 rustc_errors = { path = "../librustc_errors" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
+rustc_data_structures = { path = "../librustc_data_structures" }
\ No newline at end of file
diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index 8159893e784e4..6bc4ee0b399f9 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -10,7 +10,7 @@
 
 //! The compiler code necessary to implement the `#[derive]` extensions.
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax::ext::base::{Annotatable, ExtCtxt, SyntaxExtension, Resolver};
 use syntax::ext::build::AstBuilder;
@@ -65,7 +65,7 @@ macro_rules! derive_traits {
             $(
                 resolver.add_builtin(
                     ast::Ident::with_empty_ctxt(Symbol::intern($name)),
-                    Rc::new(SyntaxExtension::BuiltinDerive($func))
+                    Lrc::new(SyntaxExtension::BuiltinDerive($func))
                 );
             )*
         }
diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index 82d6ee5afa05b..772dec72ab98e 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -23,6 +23,7 @@ extern crate fmt_macros;
 extern crate syntax;
 extern crate syntax_pos;
 extern crate proc_macro;
+extern crate rustc_data_structures;
 extern crate rustc_errors as errors;
 
 mod asm;
@@ -44,7 +45,7 @@ pub mod deriving;
 
 pub mod proc_macro_impl;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax::ext::base::{MacroExpanderFn, NormalTT, NamedSyntaxExtension};
 use syntax::symbol::Symbol;
@@ -55,7 +56,7 @@ pub fn register_builtins(resolver: &mut syntax::ext::base::Resolver,
     deriving::register_builtin_derives(resolver);
 
     let mut register = |name, ext| {
-        resolver.add_builtin(ast::Ident::with_empty_ctxt(name), Rc::new(ext));
+        resolver.add_builtin(ast::Ident::with_empty_ctxt(name), Lrc::new(ext));
     };
 
     macro_rules! register {
diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index 85f0925b98210..623ef8c9bb3af 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -27,20 +27,20 @@
 #![feature(specialization)]
 
 use std::borrow::Cow;
-use std::cell::{Cell, RefCell};
+use std::cell::Cell;
 use std::cmp::{self, Ordering};
 use std::fmt;
 use std::hash::{Hasher, Hash};
 use std::ops::{Add, Sub};
 use std::path::PathBuf;
-use std::rc::Rc;
 
 use rustc_data_structures::stable_hasher::StableHasher;
-
-extern crate rustc_data_structures;
+use rustc_data_structures::sync::{Lrc, Lock};
 
 use serialize::{Encodable, Decodable, Encoder, Decoder};
 
+extern crate rustc_data_structures;
+
 extern crate serialize;
 extern crate serialize as rustc_serialize; // used by deriving
 
@@ -675,22 +675,22 @@ pub struct FileMap {
     /// Indicates which crate this FileMap was imported from.
     pub crate_of_origin: u32,
     /// The complete source code
-    pub src: Option<Rc<String>>,
+    pub src: Option<Lrc<String>>,
     /// The source code's hash
     pub src_hash: u128,
     /// The external source code (used for external crates, which will have a `None`
     /// value as `self.src`.
-    pub external_src: RefCell<ExternalSource>,
+    pub external_src: Lock<ExternalSource>,
     /// The start position of this source in the CodeMap
     pub start_pos: BytePos,
     /// The end position of this source in the CodeMap
     pub end_pos: BytePos,
     /// Locations of lines beginnings in the source code
-    pub lines: RefCell<Vec<BytePos>>,
+    pub lines: Lock<Vec<BytePos>>,
     /// Locations of multi-byte characters in the source code
-    pub multibyte_chars: RefCell<Vec<MultiByteChar>>,
+    pub multibyte_chars: Lock<Vec<MultiByteChar>>,
     /// Width of characters that are not narrow in the source code
-    pub non_narrow_chars: RefCell<Vec<NonNarrowChar>>,
+    pub non_narrow_chars: Lock<Vec<NonNarrowChar>>,
     /// A hash of the filename, used for speeding up the incr. comp. hashing.
     pub name_hash: u128,
 }
@@ -820,10 +820,10 @@ impl Decodable for FileMap {
                 end_pos,
                 src: None,
                 src_hash,
-                external_src: RefCell::new(ExternalSource::AbsentOk),
-                lines: RefCell::new(lines),
-                multibyte_chars: RefCell::new(multibyte_chars),
-                non_narrow_chars: RefCell::new(non_narrow_chars),
+                external_src: Lock::new(ExternalSource::AbsentOk),
+                lines: Lock::new(lines),
+                multibyte_chars: Lock::new(multibyte_chars),
+                non_narrow_chars: Lock::new(non_narrow_chars),
                 name_hash,
             })
         })
@@ -861,14 +861,14 @@ impl FileMap {
             name_was_remapped,
             unmapped_path: Some(unmapped_path),
             crate_of_origin: 0,
-            src: Some(Rc::new(src)),
+            src: Some(Lrc::new(src)),
             src_hash,
-            external_src: RefCell::new(ExternalSource::Unneeded),
+            external_src: Lock::new(ExternalSource::Unneeded),
             start_pos,
             end_pos: Pos::from_usize(end_pos),
-            lines: RefCell::new(Vec::new()),
-            multibyte_chars: RefCell::new(Vec::new()),
-            non_narrow_chars: RefCell::new(Vec::new()),
+            lines: Lock::new(Vec::new()),
+            multibyte_chars: Lock::new(Vec::new()),
+            non_narrow_chars: Lock::new(Vec::new()),
             name_hash,
         }
     }
@@ -1124,7 +1124,7 @@ impl Sub for CharPos {
 #[derive(Debug, Clone)]
 pub struct Loc {
     /// Information about the original source
-    pub file: Rc<FileMap>,
+    pub file: Lrc<FileMap>,
     /// The (1-based) line number
     pub line: usize,
     /// The (0-based) column offset
@@ -1141,14 +1141,14 @@ pub struct LocWithOpt {
     pub filename: FileName,
     pub line: usize,
     pub col: CharPos,
-    pub file: Option<Rc<FileMap>>,
+    pub file: Option<Lrc<FileMap>>,
 }
 
 // used to be structural records. Better names, anyone?
 #[derive(Debug)]
-pub struct FileMapAndLine { pub fm: Rc<FileMap>, pub line: usize }
+pub struct FileMapAndLine { pub fm: Lrc<FileMap>, pub line: usize }
 #[derive(Debug)]
-pub struct FileMapAndBytePos { pub fm: Rc<FileMap>, pub pos: BytePos }
+pub struct FileMapAndBytePos { pub fm: Lrc<FileMap>, pub pos: BytePos }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct LineInfo {
@@ -1163,7 +1163,7 @@ pub struct LineInfo {
 }
 
 pub struct FileLines {
-    pub file: Rc<FileMap>,
+    pub file: Lrc<FileMap>,
     pub lines: Vec<LineInfo>
 }
 
diff --git a/src/test/run-pass-fulldeps/issue-35829.rs b/src/test/run-pass-fulldeps/issue-35829.rs
index f17a0494a69c4..d976114822249 100644
--- a/src/test/run-pass-fulldeps/issue-35829.rs
+++ b/src/test/run-pass-fulldeps/issue-35829.rs
@@ -13,17 +13,17 @@
 #![feature(quote, rustc_private)]
 
 extern crate syntax;
+extern crate rustc_data_structures;
 
 use syntax::ext::base::{ExtCtxt, DummyResolver};
 use syntax::ext::expand::ExpansionConfig;
 use syntax::parse::ParseSess;
 use syntax::codemap::{FilePathMapping, dummy_spanned};
 use syntax::print::pprust::expr_to_string;
-use syntax::ast::{Expr, ExprKind, LitKind, StrStyle, RangeLimits};
-use syntax::symbol::Symbol;
+use syntax::ast::{ExprKind, LitKind, RangeLimits};
 use syntax::ptr::P;
 
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 
 fn main() {
     let parse_sess = ParseSess::new(FilePathMapping::empty());
@@ -33,12 +33,12 @@ fn main() {
 
     // check byte string
     let byte_string = quote_expr!(&cx, b"one");
-    let byte_string_lit_kind = LitKind::ByteStr(Rc::new(b"one".to_vec()));
+    let byte_string_lit_kind = LitKind::ByteStr(Lrc::new(b"one".to_vec()));
     assert_eq!(byte_string.node, ExprKind::Lit(P(dummy_spanned(byte_string_lit_kind))));
 
     // check raw byte string
     let raw_byte_string = quote_expr!(&cx, br###"#"two"#"###);
-    let raw_byte_string_lit_kind = LitKind::ByteStr(Rc::new(b"#\"two\"#".to_vec()));
+    let raw_byte_string_lit_kind = LitKind::ByteStr(Lrc::new(b"#\"two\"#".to_vec()));
     assert_eq!(raw_byte_string.node, ExprKind::Lit(P(dummy_spanned(raw_byte_string_lit_kind))));
 
     // check dotdoteq