[Backport v1.5] fix(streams): prevent race condition in ChannelSource on channel completion #7951
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…letion (akkadotnet#7941) * fix(streams): prevent race condition in ChannelSource on channel completion (akkadotnet#7940) Fixed a race condition in ChannelSourceLogic that caused intermittent NullReferenceException when completing a ChannelWriter while the stream was waiting for data. The issue occurred because two async callbacks could fire simultaneously when the channel writer completed: 1. The _reader.Completion continuation → OnReaderComplete → CompleteStage 2. The WaitToReadAsync continuation → OnValueRead(false) → CompleteStage Both paths could pass the IsStageCompleted check before either completed the stage, leading to concurrent access of stage internals. The fix adds an atomic flag (_completing) using Interlocked.Exchange to ensure only one completion path ever executes. This is applied to: - OnReaderComplete - channel completion callback - OnValueRead - when data is not available - OnValueReadFailure - when read fails - OnPull - synchronous completion path * refactor: use CompareExchange instead of Exchange for atomic flag CompareExchange is more semantically correct - it only sets the value if it's currently 0, rather than unconditionally setting it.
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This was referenced Nov 26, 2025
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Summary
Backport of #7941 to v1.5 branch.
Original PR: #7941