Re: How to handle waitingForLock in LockWaitCancel()

Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp> writes:
> [ backtrace snipped ]

Hmm, this is definitely not operating as intended: LockWaitCancel is
getting interrupted, because ProcessInterrupts may be called when it's
trying to acquire the lockmanager spinlock, and ProcessInterrupts will
see the ProcDiePending flag already set. I think the correct fix (or
at least part of it) is in postgres.c's die():

/*
* If it's safe to interrupt, and we're waiting for input or a lock,
* service the interrupt immediately
*/
if (ImmediateInterruptOK && InterruptHoldoffCount == 0 &&
CritSectionCount == 0)
{
+ /* bump holdoff count to make ProcessInterrupts() a no-op */
+ /* until we are done getting ready for it */
+ InterruptHoldoffCount++;
DisableNotifyInterrupt();
/* Make sure HandleDeadLock won't run while shutting down... */
LockWaitCancel();
+ InterruptHoldoffCount--;
ProcessInterrupts();
}

QueryCancelHandler probably needs similar additions.

I suspect you will find that these crashes occur during the window just
after the semop() call in IpcSemaphoreLock() --- see the comment
beginning at line 399 of ipc.c. You could probably make the crash
easier to reproduce by inserting a delay there, if you want to test
more.

regards, tom lane