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Make LimitArrayPoolWriteStream.ReturnAllPooledBuffers idempotent #128083

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Make LimitArrayPoolWriteStream.ReturnAllPooledBuffers idempotent #128083

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18 changes: 10 additions & 8 deletions src/libraries/System.Net.Http/src/System/Net/Http/HttpContent.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1077,10 +1077,12 @@ public void CopyToCore(Span<byte> destination)

private void ReturnAllPooledBuffers()
{
if (_pooledBuffers is byte[]?[] buffers)
// Use Interlocked exchanges so that concurrent Dispose() calls cannot
// double-return the same buffer to the pool. Stream.Dispose isn't required
// to be thread-safe, but a buffer returned twice corrupts the shared pool
// process-wide, so we make this method idempotent under racing callers.
if (Interlocked.Exchange(ref _pooledBuffers, null) is byte[]?[] buffers)
{
_pooledBuffers = null;

foreach (byte[]? buffer in buffers)
{
if (buffer is null)
Expand All @@ -1092,15 +1094,15 @@ private void ReturnAllPooledBuffers()
}
}

Debug.Assert(_lastBuffer is not null);
// Capture the last buffer reference before claiming the pooled flag.
// Whichever caller wins the bool exchange owns the captured reference;
// losers skip the Return and just clear the field.
byte[] lastBuffer = _lastBuffer;
_lastBuffer = null!;

if (_lastBufferIsPooled)
if (Interlocked.Exchange(ref _lastBufferIsPooled, false))
{
_lastBufferIsPooled = false;
ArrayPool<byte>.Shared.Return(lastBuffer);
}
_lastBuffer = null!;
}

public override void Write(byte[] buffer, int offset, int count)
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