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merged 3 commits into from
Jan 31, 2023
Merged

Improve Http2Connection buffer management #79484

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1b0c680
Improve Http2Connection buffer management
MihaZupan Dec 10, 2022
d98082d
Add a test
MihaZupan Dec 10, 2022
dba590b
Add a few comments around buffer disposal
MihaZupan Jan 26, 2023
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108 changes: 46 additions & 62 deletions src/libraries/Common/src/System/Net/ArrayBuffer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@

using System.Buffers;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace System.Net
Expand Down Expand Up @@ -30,8 +31,12 @@ internal struct ArrayBuffer : IDisposable

public ArrayBuffer(int initialSize, bool usePool = false)
{
Debug.Assert(initialSize > 0 || usePool);

_usePool = usePool;
_bytes = usePool ? ArrayPool<byte>.Shared.Rent(initialSize) : new byte[initialSize];
_bytes = initialSize == 0
? Array.Empty<byte>()
: usePool ? ArrayPool<byte>.Shared.Rent(initialSize) : new byte[initialSize];
Comment on lines +37 to +39
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Note ArrayPool will use Array.Empty for 0 byte requests, so this could also be:

_bytes =
    usePool ? ArrayPool<byte>.Shared.Rent(initialSize) :
    initialSize == 0 ? Array.Empty<byte>() :
    new byte[initialSize];

It's unlikely to really matter, but if we expect initialSize to most commonly be non-zero, you might want to reorder it.

_activeStart = 0;
_availableStart = 0;
}
Expand All @@ -54,12 +59,26 @@ public void Dispose()
byte[] array = _bytes;
_bytes = null!;

if (_usePool && array != null)
if (array is not null)
{
ArrayPool<byte>.Shared.Return(array);
ReturnBufferIfPooled(array);
}
}

// This is different from Dispose as the instance remains usable afterwards (_bytes will not be null).
public void ClearAndReturnBuffer()
{
Debug.Assert(_usePool);
Debug.Assert(_bytes is not null);

_activeStart = 0;
_availableStart = 0;

byte[] bufferToReturn = _bytes;
_bytes = Array.Empty<byte>();
ReturnBufferIfPooled(bufferToReturn);
}

public int ActiveLength => _availableStart - _activeStart;
public Span<byte> ActiveSpan => new Span<byte>(_bytes, _activeStart, _availableStart - _activeStart);
public ReadOnlySpan<byte> ActiveReadOnlySpan => new ReadOnlySpan<byte>(_bytes, _activeStart, _availableStart - _activeStart);
Expand Down Expand Up @@ -94,10 +113,23 @@ public void Commit(int byteCount)
}

// Ensure at least [byteCount] bytes to write to.
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void EnsureAvailableSpace(int byteCount)
{
if (byteCount <= AvailableLength)
if (byteCount > AvailableLength)
{
EnsureAvailableSpaceCore(byteCount);
}
}

private void EnsureAvailableSpaceCore(int byteCount)
{
Debug.Assert(AvailableLength < byteCount);

if (_bytes.Length == 0)
{
Debug.Assert(_usePool && _activeStart == 0 && _availableStart == 0);
_bytes = ArrayPool<byte>.Shared.Rent(byteCount);
return;
}

Expand Down Expand Up @@ -134,72 +166,24 @@ public void EnsureAvailableSpace(int byteCount)
_activeStart = 0;

_bytes = newBytes;
if (_usePool)
{
ArrayPool<byte>.Shared.Return(oldBytes);
}
ReturnBufferIfPooled(oldBytes);

Debug.Assert(byteCount <= AvailableLength);
}

// Ensure at least [byteCount] bytes to write to, up to the specified limit
public void TryEnsureAvailableSpaceUpToLimit(int byteCount, int limit)
public void Grow()
{
if (byteCount <= AvailableLength)
{
return;
}

int totalFree = _activeStart + AvailableLength;
if (byteCount <= totalFree)
{
// We can free up enough space by just shifting the bytes down, so do so.
Buffer.BlockCopy(_bytes, _activeStart, _bytes, 0, ActiveLength);
_availableStart = ActiveLength;
_activeStart = 0;
Debug.Assert(byteCount <= AvailableLength);
return;
}

if (_bytes.Length >= limit)
{
// Already at limit, can't grow further.
return;
}

// Double the size of the buffer until we have enough space, or we hit the limit
int desiredSize = Math.Min(ActiveLength + byteCount, limit);
int newSize = _bytes.Length;
do
{
newSize = Math.Min(newSize * 2, limit);
} while (newSize < desiredSize);

byte[] newBytes = _usePool ?
ArrayPool<byte>.Shared.Rent(newSize) :
new byte[newSize];
byte[] oldBytes = _bytes;

if (ActiveLength != 0)
{
Buffer.BlockCopy(oldBytes, _activeStart, newBytes, 0, ActiveLength);
}

_availableStart = ActiveLength;
_activeStart = 0;

_bytes = newBytes;
if (_usePool)
{
ArrayPool<byte>.Shared.Return(oldBytes);
}

Debug.Assert(byteCount <= AvailableLength || desiredSize == limit);
EnsureAvailableSpaceCore(AvailableLength + 1);
}

public void Grow()
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private void ReturnBufferIfPooled(byte[] buffer)
{
EnsureAvailableSpace(AvailableLength + 1);
// The buffer may be Array.Empty<byte>()
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ArrayPool is fine with Array.Empty being returned; it just gets ignored.

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I'll remove the extra check, given that we won't be calling ClearAndReturnBuffer on already-empty buffers often.

if (_usePool && buffer.Length > 0)
{
ArrayPool<byte>.Shared.Return(buffer);
}
}
}
}
75 changes: 57 additions & 18 deletions src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@ internal sealed partial class Http2Connection : HttpConnectionBase
private readonly Stream _stream;

// NOTE: These are mutable structs; do not make these readonly.
// ProcessIncomingFramesAsync and ProcessOutgoingFramesAsync are responsible for disposing/returning their respective buffers.
private ArrayBuffer _incomingBuffer;
private ArrayBuffer _outgoingBuffer;

Expand Down Expand Up @@ -89,10 +90,12 @@ internal sealed partial class Http2Connection : HttpConnectionBase

#if DEBUG
// In debug builds, start with a very small buffer to induce buffer growing logic.
private const int InitialConnectionBufferSize = 4;
private const int InitialConnectionBufferSize = FrameHeader.Size;
#else
private const int InitialConnectionBufferSize = 4096;
// Rent enough space to receive a full data frame in one read call.
private const int InitialConnectionBufferSize = FrameHeader.Size + FrameHeader.MaxPayloadLength;
#endif

// The default initial window size for streams and connections according to the RFC:
// https://datatracker.ietf.org/doc/html/rfc7540#section-5.2.1
// Unlike HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize, this value should never be changed.
Expand Down Expand Up @@ -139,8 +142,8 @@ public Http2Connection(HttpConnectionPool pool, Stream stream)
_pool = pool;
_stream = stream;

_incomingBuffer = new ArrayBuffer(InitialConnectionBufferSize);
_outgoingBuffer = new ArrayBuffer(InitialConnectionBufferSize);
_incomingBuffer = new ArrayBuffer(initialSize: 0, usePool: true);
_outgoingBuffer = new ArrayBuffer(initialSize: 0, usePool: true);

_hpackDecoder = new HPackDecoder(maxHeadersLength: pool.Settings.MaxResponseHeadersByteLength);

Expand Down Expand Up @@ -239,11 +242,15 @@ public async ValueTask SetupAsync(CancellationToken cancellationToken)
_ = ProcessIncomingFramesAsync();
await _stream.WriteAsync(_outgoingBuffer.ActiveMemory, cancellationToken).ConfigureAwait(false);
_rttEstimator.OnInitialSettingsSent();
_outgoingBuffer.Discard(_outgoingBuffer.ActiveLength);

_outgoingBuffer.ClearAndReturnBuffer();
}
catch (Exception e)
{
// ProcessIncomingFramesAsync and ProcessOutgoingFramesAsync are responsible for disposing/returning their respective buffers.
// SetupAsync is the exception as it's responsible for starting the ProcessOutgoingFramesAsync loop.
// As we're about to throw and ProcessOutgoingFramesAsync will never be called, we must return the buffer here.
_outgoingBuffer.Dispose();

Dispose();

if (e is OperationCanceledException oce && oce.CancellationToken == cancellationToken)
Expand Down Expand Up @@ -428,9 +435,13 @@ private async ValueTask<FrameHeader> ReadFrameAsync(bool initialFrame = false)
// Ensure we've read enough data for the frame header.
if (_incomingBuffer.ActiveLength < FrameHeader.Size)
{
_incomingBuffer.EnsureAvailableSpace(FrameHeader.Size - _incomingBuffer.ActiveLength);
do
{
// Issue a zero-byte read to avoid potentially pinning the buffer while waiting for more data.
await _stream.ReadAsync(Memory<byte>.Empty).ConfigureAwait(false);

_incomingBuffer.EnsureAvailableSpace(FrameHeader.Size);

int bytesRead = await _stream.ReadAsync(_incomingBuffer.AvailableMemory).ConfigureAwait(false);
_incomingBuffer.Commit(bytesRead);
if (bytesRead == 0)
Expand Down Expand Up @@ -469,6 +480,9 @@ private async ValueTask<FrameHeader> ReadFrameAsync(bool initialFrame = false)
_incomingBuffer.EnsureAvailableSpace(frameHeader.PayloadLength - _incomingBuffer.ActiveLength);
do
{
// Issue a zero-byte read to avoid potentially pinning the buffer while waiting for more data.
await _stream.ReadAsync(Memory<byte>.Empty).ConfigureAwait(false);

int bytesRead = await _stream.ReadAsync(_incomingBuffer.AvailableMemory).ConfigureAwait(false);
_incomingBuffer.Commit(bytesRead);
if (bytesRead == 0) ThrowPrematureEOF(frameHeader.PayloadLength);
Expand Down Expand Up @@ -531,9 +545,21 @@ private async Task ProcessIncomingFramesAsync()
// the entire frame's needs (not just the header).
if (_incomingBuffer.ActiveLength < FrameHeader.Size)
{
_incomingBuffer.EnsureAvailableSpace(FrameHeader.Size - _incomingBuffer.ActiveLength);
do
{
// Issue a zero-byte read to avoid potentially pinning the buffer while waiting for more data.
ValueTask<int> zeroByteReadTask = _stream.ReadAsync(Memory<byte>.Empty);
if (!zeroByteReadTask.IsCompletedSuccessfully && _incomingBuffer.ActiveLength == 0)
{
// No data is available yet. Return the receive buffer back to the pool while we wait.
_incomingBuffer.ClearAndReturnBuffer();
}
await zeroByteReadTask.ConfigureAwait(false);

// While we only need FrameHeader.Size bytes to complete this read, it's better if we rent more
// to avoid multiple ReadAsync calls and resizes once we start copying the content.
_incomingBuffer.EnsureAvailableSpace(InitialConnectionBufferSize);

int bytesRead = await _stream.ReadAsync(_incomingBuffer.AvailableMemory).ConfigureAwait(false);
Debug.Assert(bytesRead >= 0);
_incomingBuffer.Commit(bytesRead);
Expand Down Expand Up @@ -605,6 +631,10 @@ private async Task ProcessIncomingFramesAsync()

Abort(e);
}
finally
{
_incomingBuffer.Dispose();
}
}

// Note, this will return null for a streamId that's no longer in use.
Expand Down Expand Up @@ -1252,6 +1282,11 @@ private async Task ProcessOutgoingFramesAsync()
{
await FlushOutgoingBytesAsync().ConfigureAwait(false);
}

if (_outgoingBuffer.ActiveLength == 0)
{
_outgoingBuffer.ClearAndReturnBuffer();
}
}
}
catch (Exception e)
Expand All @@ -1260,6 +1295,10 @@ private async Task ProcessOutgoingFramesAsync()

Debug.Fail($"Unexpected exception in {nameof(ProcessOutgoingFramesAsync)}: {e}");
}
finally
{
_outgoingBuffer.Dispose();
}
}

private Task SendSettingsAckAsync() =>
Expand Down Expand Up @@ -1330,7 +1369,7 @@ private void WriteIndexedHeader(int index, ref ArrayBuffer headerBuffer)
int bytesWritten;
while (!HPackEncoder.EncodeIndexedHeaderField(index, headerBuffer.AvailableSpan, out bytesWritten))
{
headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
headerBuffer.Grow();
}

headerBuffer.Commit(bytesWritten);
Expand All @@ -1343,7 +1382,7 @@ private void WriteIndexedHeader(int index, string value, ref ArrayBuffer headerB
int bytesWritten;
while (!HPackEncoder.EncodeLiteralHeaderFieldWithoutIndexing(index, value, valueEncoding: null, headerBuffer.AvailableSpan, out bytesWritten))
{
headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
headerBuffer.Grow();
}

headerBuffer.Commit(bytesWritten);
Expand All @@ -1356,7 +1395,7 @@ private void WriteLiteralHeader(string name, ReadOnlySpan<string> values, Encodi
int bytesWritten;
while (!HPackEncoder.EncodeLiteralHeaderFieldWithoutIndexingNewName(name, values, HttpHeaderParser.DefaultSeparator, valueEncoding, headerBuffer.AvailableSpan, out bytesWritten))
{
headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
headerBuffer.Grow();
}

headerBuffer.Commit(bytesWritten);
Expand All @@ -1369,7 +1408,7 @@ private void WriteLiteralHeaderValues(ReadOnlySpan<string> values, string? separ
int bytesWritten;
while (!HPackEncoder.EncodeStringLiterals(values, separator, valueEncoding, headerBuffer.AvailableSpan, out bytesWritten))
{
headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
headerBuffer.Grow();
}

headerBuffer.Commit(bytesWritten);
Expand All @@ -1382,7 +1421,7 @@ private void WriteLiteralHeaderValue(string value, Encoding? valueEncoding, ref
int bytesWritten;
while (!HPackEncoder.EncodeStringLiteral(value, valueEncoding, headerBuffer.AvailableSpan, out bytesWritten))
{
headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
headerBuffer.Grow();
}

headerBuffer.Commit(bytesWritten);
Expand All @@ -1392,11 +1431,7 @@ private void WriteBytes(ReadOnlySpan<byte> bytes, ref ArrayBuffer headerBuffer)
{
if (NetEventSource.Log.IsEnabled()) Trace($"{nameof(bytes.Length)}={bytes.Length}");

if (bytes.Length > headerBuffer.AvailableLength)
{
headerBuffer.EnsureAvailableSpace(bytes.Length);
}

headerBuffer.EnsureAvailableSpace(bytes.Length);
bytes.CopyTo(headerBuffer.AvailableSpan);
headerBuffer.Commit(bytes.Length);
}
Expand Down Expand Up @@ -1855,6 +1890,10 @@ private void FinalTeardown()
_connectionWindow.Dispose();
_writeChannel.Writer.Complete();

// We're not disposing the _incomingBuffer and _outgoingBuffer here as they may still be in use by
// ProcessIncomingFramesAsync and ProcessOutgoingFramesAsync respectively, and those methods are
// responsible for returning the buffers.

if (HttpTelemetry.Log.IsEnabled())
{
if (Interlocked.Exchange(ref _markedByTelemetryStatus, TelemetryStatus_Closed) == TelemetryStatus_Opened)
Expand Down
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