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Make wrapped thread mutex acquisition unwind-safe - #9813
ThreadMutex::lock_wrapped and ThreadMutex::try_lock_for_wrapped let a caller wrap the blocking acquisition, e.g. mutex.lock_wrapped(|do_lock| vm.allow_threads(do_lock)). On main the wrapper reported success through () / bool, so safe code could obtain a guard without the raw mutex being locked, and a panic after acquisition left the mutex locked.
The callback handed to the wrapper now returns the acquired guard (Option<ThreadMutexGuard> / Result<ThreadMutexGuard, TryLockThreadError>), and the wrapped API returns whatever the wrapper returns. A guard exists only after a real acquisition, so it cannot be fabricated, and unwinding drops it.
The wrapper callback types change. In-tree callers (vm.allow_threads(do_lock) in _io) compile unchanged because allow_threads returns the closure's value.
RawThreadMutex::lock_wrapped is removed; it had no users and could not express this without trusting the wrapper.
Calling the callback again while holding its guard returns None / Err(Current) instead of blocking.
The one-second shutdown grace period in _io is unchanged.
Validation
cargo test -p rustpython-common --features threading lock::thread_mutex
The thread mutex wrapped-lock methods now pass guard-returning operations to their wrappers and check for current-thread ownership. A test verifies that the mutex can be acquired after a wrapped acquisition panics.
The mutex checks whether the current thread already owns it before invoking either wrapper. lock_wrapped now passes an operation that returns an optional guard. try_lock_for_wrapped passes an operation that returns the guard or an error, including Current for reentrant acquisition and Other for contention. The raw boolean-returning wrapped lock helper is removed. A test checks that the mutex can be acquired after a wrapped acquisition panics.
The wrapped thread-mutex methods change their callback types despite the stated intent to keep API signatures unchanged. Some existing wrappers may no longer compile. A wrapper that calls the wait operation twice can also report failure after it had successfully acquired the lock. These should be addressed before merge.
Pre-merge checks: 4
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Title check
The title "Make wrapped thread mutex acquisition unwind-safe" matches the main change. The objectives say both wrapped acquisition APIs keep a real RAII guard until the wrapper finishes, and that a pa…
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Explanation
The title "Make wrapped thread mutex acquisition unwind-safe" matches the main change. The objectives say both wrapped acquisition APIs keep a real RAII guard until the wrapper finishes, and that a panic or rejected result after acquisition releases the guard. The raw summary confirms the wrapped lock methods now return the guard from a closure, check current-thread ownership, and add a test for a panic after acquisition. The title names the primary intent and does not cover the ownership-check detail, which is acceptable.
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Track actual acquisition with a cached RAII guard rather than trusting wrapper behavior. Preserve same-thread ownership during wrapper completion, prevent repeated waits, and release on rejection or panic. Cover skipped, repeated, dishonest, reentrant, and panicking wrappers.
Assisted-by: Codex:unreported
Match CPython's ENTER_BUFFERED fast path by trying the actual lock before wrapping a blocking wait. Keep the safe wrapped fallback and existing reentrancy/shutdown behavior. Share the fast path across buffered, text and newline-decoder locks.
Assisted-by: Codex:unreported
Use the existing detached acquisition when a per-thread stop or QSBR checkpoint is pending. Add real-interpreter coverage for a native lock loop without bytecode safepoints, verify pending-stop routing, and bound the contention test wait.
Assisted-by: Codex:unreported
ThreadMutex::lock_wrapped and try_lock_for_wrapped now hand the wrapper
a callback that returns the acquired guard, and return whatever guard the
wrapper returns. Remove the OnceCell cache, RawThreadMutexGuard, and
RawThreadMutex::lock_wrapped. Restore _io.rs to main, dropping lock_io
and its tests. Reduce the thread_mutex tests to the existing timed test
and one panic test.
Assisted-by: Claude
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Actionable comments posted: 2
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @crates/common/src/lock/thread_mutex.rs:
- Around line 146-148: Update the public wrapper callback contract that uses
ThreadMutexGuard so existing blocking callbacks can return unit and timed
callbacks retain their boolean result; move guard handling into a private helper
without exposing the guard through the public callback type.
- Line 153: Update the callbacks passed to wrap_fn in the mutex acquisition
methods so repeated calls replay the first acquisition result instead of
attempting to acquire the mutex again. Retain any acquired guard internally for
the callback’s lifetime and preserve the first result’s success or failure
status, including in the timed API.
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crates/common/src/lock/thread_mutex.rs
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Summary
ThreadMutex::lock_wrappedandThreadMutex::try_lock_for_wrappedlet a caller wrap the blocking acquisition, e.g.mutex.lock_wrapped(|do_lock| vm.allow_threads(do_lock)). On main the wrapper reported success through()/bool, so safe code could obtain a guard without the raw mutex being locked, and a panic after acquisition left the mutex locked.The callback handed to the wrapper now returns the acquired guard (
Option<ThreadMutexGuard>/Result<ThreadMutexGuard, TryLockThreadError>), and the wrapped API returns whatever the wrapper returns. A guard exists only after a real acquisition, so it cannot be fabricated, and unwinding drops it.vm.allow_threads(do_lock)in_io) compile unchanged becauseallow_threadsreturns the closure's value.RawThreadMutex::lock_wrappedis removed; it had no users and could not express this without trusting the wrapper.None/Err(Current)instead of blocking._iois unchanged.Validation
cargo test -p rustpython-common --features threading lock::thread_mutexcargo clippy -p rustpython-common -p rustpython-vm --all-targets --features rustpython-vm/threading -- -D warnings-m test test_ioAI assistance: OpenAI Codex wrote the initial patch; Claude reworked it into the guard-returning API.