ByteBuffer: one fewer allocs to go to Data

Motivation:

When getting a `Data` from a `ByteBuffer` we currently allocate twice
(`__DataStorage`) and the closure for `Data.Deallocator`.

Modifications:

We can optimise that by making the closure capture exactly one
`AnyObject` which is already a reference counted object. The compiler
realises that (on Linux) and saves us an alloc.

Thanks @Lukasa for the suggestion here: #1836 (comment)

Result:

Fewer allocs.

IntegrationTests/tests_04_performance/test_01_resources/run-nio-alloc-counter-tests.sh

@@ -39,7 +39,7 @@ fi
 
 "$here/../../allocation-counter-tests-framework/run-allocation-counter.sh" \
     -p "$here/../../.." \
-    -m NIO -m NIOHTTP1 -m NIOWebSocket \
+    -m NIO -m NIOHTTP1 -m NIOWebSocket -m NIOFoundationCompat \
     -s "$here/shared.swift" \
     -t "$tmp_dir" \
     "${tests_to_run[@]}"

IntegrationTests/tests_04_performance/test_01_resources/test_bytebuffer_lots_of_rw.swift

@@ -14,6 +14,7 @@
 
 import Dispatch
 import NIO
+import NIOFoundationCompat
 
 func run(identifier: String) {
     measure(identifier: identifier) {
@@ -25,37 +26,39 @@ func run(identifier: String) {
         @inline(never)
         func doWrites(buffer: inout ByteBuffer) {
             /* these ones are zero allocations */
-            // buffer.writeBytes(foundationData) // see SR-7542
             buffer.writeBytes([0x41])
             buffer.writeBytes("A".utf8)
             buffer.writeString("A")
             buffer.writeStaticString("A")
             buffer.writeInteger(0x41, as: UInt8.self)
-
-            /* those down here should be one allocation each (on Linux) */
-            buffer.writeBytes(dispatchData) // see https://bugs.swift.org/browse/SR-9597
+            buffer.writeRepeatingByte(0x41, count: 16)
         }
         @inline(never)
         func doReads(buffer: inout ByteBuffer) {
             /* these ones are zero allocations */
-            let val = buffer.readInteger(as: UInt8.self)
+            var val = buffer.readInteger(as: UInt8.self)
+            precondition(0x41 == val, "\(val!)")
+            val = buffer.readInteger(as: UInt8.self)
             precondition(0x41 == val, "\(val!)")
             var slice = buffer.readSlice(length: 1)
             let sliceVal = slice!.readInteger(as: UInt8.self)
             precondition(0x41 == sliceVal, "\(sliceVal!)")
             buffer.withUnsafeReadableBytes { ptr in
                 precondition(ptr[0] == 0x41)
             }
+            let str = buffer.readString(length: 1)
+            precondition("A" == str, "\(str!)")
 
             /* those down here should be one allocation each */
             let arr = buffer.readBytes(length: 1)
             precondition([0x41] == arr!, "\(arr!)")
-            let str = buffer.readString(length: 1)
-            precondition("A" == str, "\(str!)")
+            let data = buffer.readData(length: 16, byteTransferStrategy: .noCopy)
+            precondition(0x41 == data?.first && 0x41 == data?.last)
         }
         for _ in 0..<1000  {
             doWrites(buffer: &buffer)
             doReads(buffer: &buffer)
+            precondition(buffer.readableBytes == 0)
         }
         return buffer.readableBytes
     }

Sources/NIOFoundationCompat/ByteBuffer-foundation.swift

@@ -126,10 +126,10 @@ extension ByteBuffer {
                 return Data(bytes: UnsafeMutableRawPointer(mutating: ptr.baseAddress!.advanced(by: index)),
                             count: Int(length))
             } else {
-                _ = storageRef.retain()
+                let storage = storageRef.takeUnretainedValue()
                 return Data(bytesNoCopy: UnsafeMutableRawPointer(mutating: ptr.baseAddress!.advanced(by: index)),
                             count: Int(length),
-                            deallocator: .custom { _, _ in storageRef.release() })
+                            deallocator: .custom { _, _ in withExtendedLifetime(storage) {} })
             }
         }
     }

docker/docker-compose.1604.52.yaml

@@ -34,7 +34,7 @@ services:
       - MAX_ALLOCS_ALLOWED_1000_udpbootstraps=2050
       - MAX_ALLOCS_ALLOWED_1000_udpconnections=96050
       - MAX_ALLOCS_ALLOWED_1_reqs_1000_conn=455000
-      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=2050
+      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=3050
       - MAX_ALLOCS_ALLOWED_creating_10000_headers=0
       - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2050
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer=3

docker/docker-compose.1604.53.yaml

@@ -34,7 +34,7 @@ services:
       - MAX_ALLOCS_ALLOWED_1000_udpbootstraps=2050
       - MAX_ALLOCS_ALLOWED_1000_udpconnections=95050
       - MAX_ALLOCS_ALLOWED_1_reqs_1000_conn=450050
-      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=2050
+      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=3050
       - MAX_ALLOCS_ALLOWED_creating_10000_headers=0
       - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2050
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer=3

docker/docker-compose.1804.51.yaml

@@ -34,7 +34,7 @@ services:
       - MAX_ALLOCS_ALLOWED_1000_udpbootstraps=2050
       - MAX_ALLOCS_ALLOWED_1000_udpconnections=96050
       - MAX_ALLOCS_ALLOWED_1_reqs_1000_conn=452050
-      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=2050
+      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=3050
       - MAX_ALLOCS_ALLOWED_creating_10000_headers=10050
       - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2050
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer=3

docker/docker-compose.2004.54.yaml

@@ -34,7 +34,7 @@ services:
       - MAX_ALLOCS_ALLOWED_1000_udpbootstraps=2050
       - MAX_ALLOCS_ALLOWED_1000_udpconnections=96050
       - MAX_ALLOCS_ALLOWED_1_reqs_1000_conn=453050 # regression from 5.3 which was 450050
-      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=2050
+      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=3050
       - MAX_ALLOCS_ALLOWED_creating_10000_headers=0
       - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2050
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer=3

docker/docker-compose.2004.main.yaml

@@ -34,7 +34,7 @@ services:
       - MAX_ALLOCS_ALLOWED_1000_udpbootstraps=2050
       - MAX_ALLOCS_ALLOWED_1000_udpconnections=96050
       - MAX_ALLOCS_ALLOWED_1_reqs_1000_conn=453000
-      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=2050
+      - MAX_ALLOCS_ALLOWED_bytebuffer_lots_of_rw=3050
       - MAX_ALLOCS_ALLOWED_creating_10000_headers=0
       - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2050
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer=3