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Don't reset latch in ConditionVariablePrepareToSleep().

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It's not OK to do that without calling CHECK_FOR_INTERRUPTS().
Let the next wait loop deal with it, following the usual pattern.

One consequence of this bug was that a SIGTERM delivered in a very
narrow timing window could leave a parallel worker process waiting
forever for a condition variable that will never be signaled, after
an error was raised in other process.

The code is a bit different in the stable branches due to commit
1321509f, making problems less likely there.  No back-patch for now,
but we may finish up deciding to make a similar change after more
discussion.

Author: Thomas Munro
Reviewed-by: Shawn Debnath
Reported-by: Tomas Vondra
Discussion: https://postgr.es/m/CA%2BhUKGJOm8zZHjVA8svoNT3tHY0XdqmaC_kHitmgXDQM49m1dA%40mail.gmail.com
This commit is contained in:
Thomas Munro 2020-01-28 15:28:36 +13:00
parent 05f18c6b6b
commit 78aaa0e823
1 changed files with 0 additions and 6 deletions
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6
src/backend/storage/lmgr/condition_variable.c
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@ -93,12 +93,6 @@ ConditionVariablePrepareToSleep(ConditionVariable *cv)
/* Record the condition variable on which we will sleep. */
cv_sleep_target = cv;
/*
* Reset my latch before adding myself to the queue, to ensure that we
* don't miss a wakeup that occurs immediately.
*/
ResetLatch(MyLatch);
/* Add myself to the wait queue. */
SpinLockAcquire(&cv->mutex);
proclist_push_tail(&cv->wakeup, pgprocno, cvWaitLink);