{
internal struct BufferSegmentStack
{
- private BufferSegment[] _array;
+ private SegmentAsValueType[] _array;
private int _size;
public BufferSegmentStack(int size)
{
- _array = new BufferSegment[size];
+ _array = new SegmentAsValueType[size];
_size = 0;
}
public bool TryPop(out BufferSegment result)
{
int size = _size - 1;
- BufferSegment[] array = _array;
+ SegmentAsValueType[] array = _array;
if ((uint)size >= (uint)array.Length)
{
public void Push(BufferSegment item)
{
int size = _size;
- BufferSegment[] array = _array;
+ SegmentAsValueType[] array = _array;
if ((uint)size < (uint)array.Length)
{
_array[_size] = item;
_size++;
}
+
+ /// <summary>
+ /// A simple struct we wrap reference types inside when storing in arrays to
+ /// bypass the CLR's covariant checks when writing to arrays.
+ /// </summary>
+ /// <remarks>
+ /// We use <see cref="SegmentAsValueType"/> as a wrapper to avoid paying the cost of covariant checks whenever
+ /// the underlying array that the <see cref="BufferSegmentStack"/> class uses is written to.
+ /// We've recognized this as a perf win in ETL traces for these stack frames:
+ /// clr!JIT_Stelem_Ref
+ /// clr!ArrayStoreCheck
+ /// clr!ObjIsInstanceOf
+ /// </remarks>
+ private readonly struct SegmentAsValueType
+ {
+ private readonly BufferSegment _value;
+ private SegmentAsValueType(BufferSegment value) => _value = value;
+ public static implicit operator SegmentAsValueType(BufferSegment s) => new SegmentAsValueType(s);
+ public static implicit operator BufferSegment(SegmentAsValueType s) => s._value;
+ }
}
}
--- /dev/null
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace System.IO.Pipelines.Tests
+{
+ public class BufferSegmentPoolTest : IDisposable
+ {
+ private readonly TestMemoryPool _pool;
+ private readonly Pipe _pipe;
+
+ public BufferSegmentPoolTest()
+ {
+ _pool = new TestMemoryPool();
+ _pipe = new Pipe(new PipeOptions(_pool, readerScheduler: PipeScheduler.Inline, writerScheduler: PipeScheduler.Inline, pauseWriterThreshold: 0, resumeWriterThreshold: 0, useSynchronizationContext: false));
+ }
+
+ public void Dispose()
+ {
+ _pipe.Writer.Complete();
+ _pipe.Reader.Complete();
+ _pool?.Dispose();
+ }
+
+ [Fact]
+ public async Task BufferSegmentsAreReused()
+ {
+ _pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
+ await _pipe.Writer.FlushAsync();
+
+ ReadResult result = await _pipe.Reader.ReadAsync();
+ object oldSegment = result.Buffer.End.GetObject();
+
+ // This should return the first segment
+ _pipe.Reader.AdvanceTo(result.Buffer.End);
+
+ // One block remaining
+ Assert.Equal(0, _pipe.Length);
+
+ // This should use the segment that was returned
+ _pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
+ await _pipe.Writer.FlushAsync();
+
+ result = await _pipe.Reader.ReadAsync();
+ object newSegment = result.Buffer.End.GetObject();
+ _pipe.Reader.AdvanceTo(result.Buffer.End);
+
+ Assert.Same(oldSegment, newSegment);
+
+ Assert.Equal(0, _pipe.Length);
+ }
+
+ [Fact]
+ public async Task BufferSegmentsPooledUpToThreshold()
+ {
+ int blockCount = Pipe.MaxSegmentPoolSize + 1;
+
+ // Write 256 blocks to ensure they get reused
+ for (int i = 0; i < blockCount; i++)
+ {
+ _pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
+ }
+
+ await _pipe.Writer.FlushAsync();
+
+ ReadResult result = await _pipe.Reader.ReadAsync();
+
+ List<ReadOnlySequenceSegment<byte>> oldSegments = GetSegments(result);
+
+ Assert.Equal(blockCount, oldSegments.Count);
+
+ // This should return them all to the segment pool (256 blocks, the last block will be discarded)
+ _pipe.Reader.AdvanceTo(result.Buffer.End);
+
+ for (int i = 0; i < blockCount; i++)
+ {
+ _pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
+ }
+
+ await _pipe.Writer.FlushAsync();
+
+ result = await _pipe.Reader.ReadAsync();
+
+ List<ReadOnlySequenceSegment<byte>> newSegments = GetSegments(result);
+
+ Assert.Equal(blockCount, newSegments.Count);
+
+ _pipe.Reader.AdvanceTo(result.Buffer.End);
+
+ // Assert Pipe.MaxSegmentPoolSize pooled segments
+ for (int i = 0; i < Pipe.MaxSegmentPoolSize; i++)
+ {
+ Assert.Same(oldSegments[i], newSegments[Pipe.MaxSegmentPoolSize - i - 1]);
+ }
+
+ // The last segment shouldn't exist in the new list of segments at all (it should be new)
+ Assert.DoesNotContain(oldSegments[256], newSegments);
+ }
+
+ private static List<ReadOnlySequenceSegment<byte>> GetSegments(ReadResult result)
+ {
+ SequenceMarshal.TryGetReadOnlySequenceSegment(
+ result.Buffer,
+ out ReadOnlySequenceSegment<byte> start,
+ out int startIndex,
+ out ReadOnlySequenceSegment<byte> end,
+ out int endIndex);
+
+ var segments = new List<ReadOnlySequenceSegment<byte>>();
+
+ while (start != end.Next)
+ {
+ segments.Add(start);
+ start = start.Next;
+ }
+
+ return segments;
+ }
+ }
+}
}
[Fact]
- public async Task BufferSegmentsAreReused()
- {
- _pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
- await _pipe.Writer.FlushAsync();
-
- ReadResult result = await _pipe.Reader.ReadAsync();
- object oldSegment = result.Buffer.End.GetObject();
-
- // This should return the first segment
- _pipe.Reader.AdvanceTo(result.Buffer.End);
-
- // One block remaining
- Assert.Equal(0, _pipe.Length);
-
- // This should use the segment that was returned
- _pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
- await _pipe.Writer.FlushAsync();
-
- result = await _pipe.Reader.ReadAsync();
- object newSegment = result.Buffer.End.GetObject();
- _pipe.Reader.AdvanceTo(result.Buffer.End);
-
- Assert.Same(oldSegment, newSegment);
-
- Assert.Equal(0, _pipe.Length);
- }
-
- [Fact]
public async Task PooledSegmentsDontAffectLastExaminedSegment()
{
_pipe.Writer.WriteEmpty(_pool.MaxBufferSize);
projects / platform / upstream / dotnet / runtime.git / commitdiff