llvm-project

de4a1a77 - [clang][modules] Prevent deadlock in module cache (#182722)

[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