Remove automatic (delayed) reseed-on-fork (#1379)

* benches/generators.rs: standardize thread_rng benchmarks
* Remove cfgs from examples
* Remove ReadRng
* Add ThreadRng::reseed and doc to use
* Remove fork protection from ReseedingRng; remove libc dep
* Enable ReseedingRng without std
* Move ReseedingRng up; remove module rand::rngs::adapter

Author: dhardy

CHANGELOG.md

@@ -11,6 +11,10 @@ You may also find the [Upgrade Guide](https://rust-random.github.io/book/update.
 ## [0.9.1] - unreleased
 - Add the `Slice::num_choices` method to the Slice distribution (#1402)
 
+### Generators
+- `ReseedingRng::reseed` also resets the random data cache.
+- Remove fork-protection from `ReseedingRng` and `ThreadRng`. Instead, it is recommended to call `ThreadRng::reseed` on fork.
+
 ## [0.9.0-alpha.0] - 2024-02-18
 This is a pre-release. To depend on this version, use `rand = "=0.9.0-alpha.0"` to prevent automatic updates (which can be expected to include breaking changes).
 

Cargo.toml

@@ -21,7 +21,7 @@ include = ["src/", "LICENSE-*", "README.md", "CHANGELOG.md", "COPYRIGHT"]
 # To build locally:
 # RUSTDOCFLAGS="--cfg doc_cfg -Zunstable-options --generate-link-to-definition" cargo +nightly doc --all --all-features --no-deps --open
 all-features = true
-rustdoc-args = ["--cfg", "doc_cfg", "--generate-link-to-definition"]
+rustdoc-args = ["--cfg", "doc_cfg", "-Zunstable-options", "--generate-link-to-definition"]
 
 [package.metadata.playground]
 features = ["small_rng", "serde1"]
@@ -34,7 +34,7 @@ serde1 = ["serde", "rand_core/serde1"]
 
 # Option (enabled by default): without "std" rand uses libcore; this option
 # enables functionality expected to be available on a standard platform.
-std = ["rand_core/std", "rand_chacha?/std", "alloc", "libc"]
+std = ["rand_core/std", "rand_chacha?/std", "alloc"]
 
 # Option: "alloc" enables support for Vec and Box when not using "std"
 alloc = ["rand_core/alloc"]
@@ -71,10 +71,6 @@ serde = { version = "1.0.103", features = ["derive"], optional = true }
 rand_chacha = { path = "rand_chacha", version = "=0.9.0-alpha.0", default-features = false, optional = true }
 zerocopy = { version = "=0.8.0-alpha.6", default-features = false, features = ["simd"] }
 
-[target.'cfg(unix)'.dependencies]
-# Used for fork protection (reseeding.rs)
-libc = { version = "0.2.22", optional = true, default-features = false }
-
 [dev-dependencies]
 rand_pcg = { path = "rand_pcg", version = "=0.9.0-alpha.0" }
 # Only to test serde1

SECURITY.md

@@ -23,9 +23,6 @@ are expected to provide the following:
 For some RNGs, notably `OsRng`, `ThreadRng` and those wrapped by `ReseedingRng`,
 we provide limited mitigations against side-channel attacks:
 
--   After a process fork on Unix, there is an upper-bound on the number of bits
-    output by the RNG before the processes diverge, after which outputs from
-    each process's RNG are uncorrelated
 -   After the state (memory) of an RNG is leaked, there is an upper-bound on the
     number of bits of output by the RNG before prediction of output by an
     observer again becomes computationally-infeasible

benches/generators.rs

@@ -18,7 +18,7 @@ use core::mem::size_of;
 use test::{black_box, Bencher};
 
 use rand::prelude::*;
-use rand::rngs::adapter::ReseedingRng;
+use rand::rngs::ReseedingRng;
 use rand::rngs::{mock::StepRng, OsRng};
 use rand_chacha::{ChaCha12Rng, ChaCha20Core, ChaCha20Rng, ChaCha8Rng};
 use rand_pcg::{Pcg32, Pcg64, Pcg64Mcg, Pcg64Dxsm};
@@ -52,6 +52,7 @@ gen_bytes!(gen_bytes_std, StdRng::from_entropy());
 #[cfg(feature = "small_rng")]
 gen_bytes!(gen_bytes_small, SmallRng::from_thread_rng());
 gen_bytes!(gen_bytes_os, OsRng);
+gen_bytes!(gen_bytes_thread, thread_rng());
 
 macro_rules! gen_uint {
     ($fnn:ident, $ty:ty, $gen:expr) => {
@@ -82,6 +83,7 @@ gen_uint!(gen_u32_std, u32, StdRng::from_entropy());
 #[cfg(feature = "small_rng")]
 gen_uint!(gen_u32_small, u32, SmallRng::from_thread_rng());
 gen_uint!(gen_u32_os, u32, OsRng);
+gen_uint!(gen_u32_thread, u32, thread_rng());
 
 gen_uint!(gen_u64_step, u64, StepRng::new(0, 1));
 gen_uint!(gen_u64_pcg32, u64, Pcg32::from_entropy());
@@ -95,6 +97,7 @@ gen_uint!(gen_u64_std, u64, StdRng::from_entropy());
 #[cfg(feature = "small_rng")]
 gen_uint!(gen_u64_small, u64, SmallRng::from_thread_rng());
 gen_uint!(gen_u64_os, u64, OsRng);
+gen_uint!(gen_u64_thread, u64, thread_rng());
 
 macro_rules! init_gen {
     ($fnn:ident, $gen:ident) => {
@@ -141,24 +144,3 @@ reseeding_bytes!(reseeding_chacha20_32k, 32);
 reseeding_bytes!(reseeding_chacha20_64k, 64);
 reseeding_bytes!(reseeding_chacha20_256k, 256);
 reseeding_bytes!(reseeding_chacha20_1M, 1024);
-
-
-macro_rules! threadrng_uint {
-    ($fnn:ident, $ty:ty) => {
-        #[bench]
-        fn $fnn(b: &mut Bencher) {
-            let mut rng = thread_rng();
-            b.iter(|| {
-                let mut accum: $ty = 0;
-                for _ in 0..RAND_BENCH_N {
-                    accum = accum.wrapping_add(rng.gen::<$ty>());
-                }
-                accum
-            });
-            b.bytes = size_of::<$ty>() as u64 * RAND_BENCH_N;
-        }
-    };
-}
-
-threadrng_uint!(thread_rng_u32, u32);
-threadrng_uint!(thread_rng_u64, u64);

examples/monte-carlo.rs

@@ -23,9 +23,6 @@
 //! We can use the above fact to estimate the value of π: pick many points in
 //! the square at random, calculate the fraction that fall within the circle,
 //! and multiply this fraction by 4.
-
-#![cfg(all(feature = "std", feature = "std_rng"))]
-
 use rand::distributions::{Distribution, Uniform};
 
 fn main() {

examples/monty-hall.rs

@@ -26,8 +26,6 @@
 //!
 //! [Monty Hall Problem]: https://en.wikipedia.org/wiki/Monty_Hall_problem
 
-#![cfg(all(feature = "std", feature = "std_rng"))]
-
 use rand::distributions::{Distribution, Uniform};
 use rand::Rng;
 

examples/rayon-monte-carlo.rs

@@ -38,8 +38,6 @@
 //! over BATCH_SIZE trials. Manually batching also turns out to be faster
 //! for the nondeterministic version of this program as well.
 
-#![cfg(all(feature = "std", feature = "std_rng"))]
-
 use rand::distributions::{Distribution, Uniform};
 use rand_chacha::{rand_core::SeedableRng, ChaCha8Rng};
 use rayon::prelude::*;

src/rngs/adapter/mod.rs

@@ -96,8 +96,8 @@
 //! [`rand_xoshiro`]: https://crates.io/crates/rand_xoshiro
 //! [`rng` tag]: https://crates.io/keywords/rng
 
-#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-#[cfg(feature = "std")] pub mod adapter;
+mod reseeding;
+pub use reseeding::ReseedingRng;
 
 pub mod mock; // Public so we don't export `StepRng` directly, making it a bit
               // more clear it is intended for testing.