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Sumi JeongandJeong, YunWon
9d9fc27082
* _queue: check for pending signals during blocking get() Semaphore::acquire() waited on the condvar in a single uninterrupted call, so a Python-level signal handler never ran until the wait itself returned. check_signals() is only invoked from the bytecode dispatch loop, and this native wait never passed through it -- CPython chunks its equivalent blocking wait for the same reason. Cap each wait at a short interval and call check_signals() between chunks, only giving up once the caller's real deadline has actually elapsed. The mutex guard must be dropped before check_signals() runs: a signal handler that calls back into the same queue on the same thread would otherwise try to relock a mutex it's still holding and deadlock against itself. Add a regression snippet that arms a SIGALRM well before a helper thread unblocks the queue, and asserts the handler ran near the alarm instead of only once get() returned. Refs #8250 Assisted-by: Claude * _queue: correct SIGNAL_CHECK_INTERVAL doc comment The old comment claimed this mirrors CPython's PyThread_acquire_lock_timed, but CPython doesn't chunk its wait either -- it makes one sem_timedwait call and relies on the OS reporting EINTR. parking_lot's Condvar has no equivalent signal to surface, so polling is a workaround for that gap, not a mirror of CPython's approach. Assisted-by: Claude * Apply suggestions from code review Co-authored-by: Jeong, YunWon <69878+youknowone@users.noreply.github.com> * _queue: fix comment indentation (cargo fmt) Assisted-by: Claude --------- Co-authored-by: Jeong, YunWon <69878+youknowone@users.noreply.github.com>
53 lines
1.4 KiB
Python
53 lines
1.4 KiB
Python
"""A blocking queue.SimpleQueue.get() must stay responsive to signals.
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SimpleQueue.get() waits on a Condvar. A single uninterrupted wait blocks
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Python-level signal handlers (including the default KeyboardInterrupt) until
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the wait itself returns, since signals are only delivered at bytecode
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safepoints. A regression shows up as the handler firing only once get()
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unblocks, instead of promptly when the signal actually arrives.
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"""
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import queue
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import signal
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import sys
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import threading
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import time
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if sys.platform.startswith("win"):
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print("skipped (no SIGALRM)")
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raise SystemExit(0)
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q = queue.SimpleQueue()
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start = time.time()
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handled_at = []
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def handler(signum, frame):
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handled_at.append(time.time() - start)
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signal.signal(signal.SIGALRM, handler)
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signal.setitimer(signal.ITIMER_REAL, 0.3)
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def unblock_later():
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time.sleep(1.5)
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q.put("unblock")
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threading.Thread(target=unblock_later, daemon=True).start()
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item = q.get() # blocks until unblock_later() wakes us up
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elapsed = time.time() - start
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assert item == "unblock", item
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assert handled_at, "signal handler never ran"
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# The handler should fire around t=0.3s, when the timer was started, not t=1.5s
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# (when get() finally unblocked).
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assert handled_at[0] < elapsed - 0.5, (
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f"signal handled at {handled_at[0]:.2f}s but get() only returned at "
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f"{elapsed:.2f}s -- signal was not processed while blocked"
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)
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print("ok")
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