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Commit76d07a2

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Fix status reporting for terminated bgworkers that were never started.
Previously, GetBackgroundWorkerPid() would return BGWH_NOT_YET_STARTEDif the slot used for the worker registration had not been reused byunrelated activity, and BGWH_STOPPED if it had. Either way, a processthat had requested notification when the state of one of itsbackground workers changed did not receive such notifications. Fixthings so that GetBackgroundWorkerPid() always returns BGWH_STOPPED inthis situation, so that we do not erroneously give waiters theimpression that the worker will eventually be started; and sendnotifications just as we would if the process terminated after havingbeen started, so that it's possible to wait for the postmaster toprocess 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 anyonerelying on this interface yet, but if anyone is, the new behavior is aclear improvement.
1 parent904e8b6 commit76d07a2

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‎src/backend/postmaster/bgworker.c

Lines changed: 24 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -245,14 +245,37 @@ BackgroundWorkerStateChange(void)
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rw->rw_terminate= true;
246246
if (rw->rw_pid!=0)
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kill(rw->rw_pid,SIGTERM);
248+
else
249+
{
250+
/* Report never-started, now-terminated worker as dead. */
251+
ReportBackgroundWorkerPID(rw);
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}
248253
}
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continue;
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}
251256

252-
/* If it's already flagged as do not restart, just release the slot. */
257+
/*
258+
* If the worker is marked for termination, we don't need to add it
259+
* to the registered workers list; we can just free the slot.
260+
* However, if bgw_notify_pid is set, the process that registered the
261+
* worker may need to know that we've processed the terminate request,
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* so be sure to signal it.
263+
*/
253264
if (slot->terminate)
254265
{
266+
intnotify_pid;
267+
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/*
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* We need a memory barrier here to make sure that the load of
270+
* bgw_notify_pid completes before the store to in_use.
271+
*/
272+
notify_pid=slot->worker.bgw_notify_pid;
273+
pg_memory_barrier();
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slot->pid=0;
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slot->in_use= false;
276+
if (notify_pid!=0)
277+
kill(notify_pid,SIGUSR1);
278+
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continue;
257280
}
258281

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