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bpo-41299: fix 16ms jitter in Windows threading timeouts #26568

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Merged
zooba merged 1 commit into from
Jun 7, 2021
Merged

bpo-41299: fix 16ms jitter in Windows threading timeouts #26568

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Windows/2021-06-06-16-36-13.bpo-41299.Rg-vb_.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix 16ms jitter when using timeouts in :mod:`threading`, such as with :meth:`threading.Lock.acquire` or :meth:`threading.Condition.wait`.
14 changes: 10 additions & 4 deletions Python/thread_nt.h
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Expand Up @@ -76,16 +76,22 @@ EnterNonRecursiveMutex(PNRMUTEX mutex, DWORD milliseconds)
}
} else if (milliseconds != 0) {
/* wait at least until the target */
ULONGLONG now, target = GetTickCount64() + milliseconds;
_PyTime_t now = _PyTime_GetPerfCounter();
if (now <= 0) {
Py_FatalError("_PyTime_GetPerfCounter() == 0");
}
_PyTime_t nanoseconds = _PyTime_FromNanoseconds((_PyTime_t)milliseconds * 1000000);
_PyTime_t target = now + nanoseconds;
while (mutex->locked) {
if (PyCOND_TIMEDWAIT(&mutex->cv, &mutex->cs, (long long)milliseconds*1000) < 0) {
_PyTime_t microseconds = _PyTime_AsMicroseconds(nanoseconds, _PyTime_ROUND_TIMEOUT);
if (PyCOND_TIMEDWAIT(&mutex->cv, &mutex->cs, microseconds) < 0) {
result = WAIT_FAILED;
break;
}
now = GetTickCount64();
now = _PyTime_GetPerfCounter();
if (target <= now)
break;
milliseconds = (DWORD)(target-now);
nanoseconds = target - now;
}
}
if (!mutex->locked) {
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