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Commitbf740ce

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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.
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‎src/backend/postmaster/bgworker.c

Lines changed: 24 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -244,14 +244,37 @@ BackgroundWorkerStateChange(void)
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rw->rw_terminate= true;
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if (rw->rw_pid!=0)
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kill(rw->rw_pid,SIGTERM);
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else
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{
249+
/* Report never-started, now-terminated worker as dead. */
250+
ReportBackgroundWorkerPID(rw);
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}
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}
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continue;
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}
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251-
/* If it's already flagged as do not restart, just release the slot. */
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/*
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* If the worker is marked for termination, we don't need to add it
258+
* to the registered workers list; we can just free the slot.
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* However, if bgw_notify_pid is set, the process that registered the
260+
* worker may need to know that we've processed the terminate request,
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* so be sure to signal it.
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*/
252263
if (slot->terminate)
253264
{
265+
intnotify_pid;
266+
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/*
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* We need a memory barrier here to make sure that the load of
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* bgw_notify_pid completes before the store to in_use.
270+
*/
271+
notify_pid=slot->worker.bgw_notify_pid;
272+
pg_memory_barrier();
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slot->pid=0;
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slot->in_use= false;
275+
if (notify_pid!=0)
276+
kill(notify_pid,SIGUSR1);
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continue;
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}
257280

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