[clang][modules] Prevent deadlock in module cache (#182722)#12833
Merged
jansvoboda11 merged 1 commit intostable/21.xfrom Apr 27, 2026
Merged
[clang][modules] Prevent deadlock in module cache (#182722)#12833jansvoboda11 merged 1 commit intostable/21.xfrom
jansvoboda11 merged 1 commit intostable/21.xfrom
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When there's a dependency cycle between modules, the dependency scanner may encounter a deadlock. This was caused by not respecting the lock timeout. But even with the timeout implemented, leaving `unsafeMaybeUnlock()` unimplemented means trying to take a lock after a timeout would still fail and prevent making progress. This PR implements this API in a way to avoid UB on `std::mutex` (when it's unlocked by someone else than the owner). Lastly, this PR makes sure that `unsafeUnlock()` ends the wait of existing threads, so that they don't need to hit the full timeout amount. This PR also implements `-fimplicit-modules-lock-timeout=<seconds>` that allows tweaking the default 90-second lock timeout, and adds `#pragma clang __debug sleep` that makes it easier to achieve desired execution ordering. rdar://170738600 (cherry picked from commit de4a1a7)
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@swift-ci please test |
Author
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@swift-ci please test |
Author
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swiftlang/swift#88652 |
akyrtzi
approved these changes
Apr 27, 2026
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When there's a dependency cycle between modules, the dependency scanner may encounter a deadlock. This was caused by not respecting the lock timeout. But even with the timeout implemented, leaving
unsafeMaybeUnlock()unimplemented means trying to take a lock after a timeout would still fail and prevent making progress. This PR implements this API in a way to avoid UB onstd::mutex(when it's unlocked by someone else than the owner). Lastly, this PR makes sure thatunsafeUnlock()ends the wait of existing threads, so that they don't need to hit the full timeout amount.This PR also implements
-fimplicit-modules-lock-timeout=<seconds>that allows tweaking the default 90-second lock timeout, and adds#pragma clang __debug sleepthat makes it easier to achieve desired execution ordering.rdar://170738600
(cherry picked from commit de4a1a7)