Jan Svoboda de4a1a77e1 [clang][modules] Prevent deadlock in module cache (#182722) ...

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

2026-02-27 09:36:14 -08:00

22 KiB

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