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[patch] Return from Cancel() before the cancelled run unwinds, so cancelling under a lock can't deadlock - #111
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…so Cancel() returns before the unwind The reader's cancellation TaskCompletionSource was completed from inside CancellationTokenSource.Cancel() without RunContinuationsAsynchronously, so the whole unwind ran on the cancelling thread before Cancel() returned: the read drain, the process-tree kill, and the caller's own catch block. A caller that cancelled while holding a lock its cleanup also takes deadlocked. Fixes #103 Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01Bm33TiYrofqKs4oGc3UGUU
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This was referenced Oct 6, 2026
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Fixes #103
Problem
AsyncProcessStreamReader.Startcreated its cancellation signal asnew TaskCompletionSource<bool>(). The token registration completes it from insideCancellationTokenSource.Cancel(), so every continuation ran synchronously on the cancelling thread: the read drain,RunAsync's catch with the process-tree kill, and then the caller's ownawait/catch. All of that happened beforeCancel()returned. A caller that cancelled while holding a lock its cleanup also takes deadlocked, andCancelAfterran user code on the timer thread.Change
TaskCreationOptions.RunContinuationsAsynchronously, with a comment explaining why.Tests
Two new tests in
RunCommandTests, following the issue's acceptance criteria:CancelShouldNotRunTheCallersContinuationInline: the caller'scatch (OperationCanceledException)records whether it ran whileCancel()was still on the stack.CancelWhileHoldingALockTheCallersCleanupNeedsShouldNotDeadlock: the cancelling thread holds aSemaphoreSlimthat the caller's catch takes synchronously. The wait in the catch is bounded at 5 s, so the bug shows up as a failure and doesn't hang the run.Checked locally (Linux, net10.0):
Cancel()was blocked behind the cleanup.🤖 Generated with Claude Code
https://claude.ai/code/session_01Bm33TiYrofqKs4oGc3UGUU
Generated by Claude Code