Fix parDemuxScan deadlock when worker throws with full buffer#3189
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harendra-kumar merged 1 commit intocomposewell:masterfrom Apr 19, 2026
Merged
Fix parDemuxScan deadlock when worker throws with full buffer#3189harendra-kumar merged 1 commit intocomposewell:masterfrom
harendra-kumar merged 1 commit intocomposewell:masterfrom
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Thanks for the PR @johnhampton . I will take a deeper look and get back to you. |
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@johnhampton I have fixed the failing CIs on master, you can rebase this on master. |
Signal the driver thread when a worker exception occurs so it can wake up from blocking on a full input buffer. Previously sendExceptionToDriver only wrote to the output queue, leaving the driver stuck on takeMVar. - Set closedForInput and signal inputSpaceDoorBell in sendExceptionToDriver - Add regression test with slow single-key worker that throws mid-stream - Test confirms original exception propagates instead of BlockedIndefinitelyOnMVar
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@harendra-kumar I've rebased and all the tests pass. I'm sorry for the delay, I missed the GitHub notification. |
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Thanks @johnhampton . I am merging this. |
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When a fold worker throws an exception while the driver is blocked on a full input buffer,
sendExceptionToDriverwrites to the output queue but never signals the driver. The driver remains stuck ontakeMVar, and GHC's runtime eventually throwsBlockedIndefinitelyOnMVar, masking the original exception entirely.Signal
inputSpaceDoorBelland setclosedForInputinsendExceptionToDriverso the driver can wake up. Add regression test.This fix was implemented with AI assistance (Claude, Anthropic).