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Fix status reporting for terminated bgworkers that were never started.

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Previously, GetBackgroundWorkerPid() would return BGWH_NOT_YET_STARTED
if the slot used for the worker registration had not been reused by
unrelated activity, and BGWH_STOPPED if it had.  Either way, a process
that had requested notification when the state of one of its
background workers changed did not receive such notifications.  Fix
things so that GetBackgroundWorkerPid() always returns BGWH_STOPPED in
this situation, so that we do not erroneously give waiters the
impression that the worker will eventually be started; and send
notifications just as we would if the process terminated after having
been started, so that it's possible to wait for the postmaster to
process a worker termination request without polling.

Discovered by Amit Kapila during testing of parallel sequential scan.
Analysis and fix by me.  Back-patch to 9.4; there may not be anyone
relying on this interface yet, but if anyone is, the new behavior is a
clear improvement.
This commit is contained in:
Robert Haas 2015-03-19 10:56:34 -04:00
parent 417f78a517
commit bf740ce9e5
1 changed files with 24 additions and 1 deletions
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25
src/backend/postmaster/bgworker.c
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@ -244,14 +244,37 @@ BackgroundWorkerStateChange(void)
rw->rw_terminate = true;
if (rw->rw_pid != 0)
kill(rw->rw_pid, SIGTERM);
else
{
/* Report never-started, now-terminated worker as dead. */
ReportBackgroundWorkerPID(rw);
}
}
continue;
}
/* If it's already flagged as do not restart, just release the slot. */
/*
* If the worker is marked for termination, we don't need to add it
* to the registered workers list; we can just free the slot.
* However, if bgw_notify_pid is set, the process that registered the
* worker may need to know that we've processed the terminate request,
* so be sure to signal it.
*/
if (slot->terminate)
{
int notify_pid;
/*
* We need a memory barrier here to make sure that the load of
* bgw_notify_pid completes before the store to in_use.
*/
notify_pid = slot->worker.bgw_notify_pid;
pg_memory_barrier();
slot->pid = 0;
slot->in_use = false;
if (notify_pid != 0)
kill(notify_pid, SIGUSR1);
continue;
}