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Commitcd89965

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Fix bogus when-to-deregister-from-listener-array logic.
Since a backend adds itself to the global listener array duringExec_ListenPreCommit, it's inappropriate for it to remove itself duringExec_UnlistenCommit or Exec_UnlistenAllCommit --- that leads to failurewhen committing a transaction that did UNLISTEN then LISTEN, since we endup not registered though we should be. (This leads to missing laternotifications, or to Assert failures in assert-enabled builds.) Insteaddeal with deregistering at the bottom of AtCommit_Notify, when we know thefinal state of the listenChannels list.Also, simplify the representation of registration status by replacing thetransient backendHasExecutedInitialListen flag with an amRegisteredListenerflag.Per report from Greg Sabino Mullane. Back-patch to 9.0, where the problemwas introduced during the LISTEN/NOTIFY rewrite.
1 parentfdf9e21 commitcd89965

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-38
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1 file changed

+22
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‎src/backend/commands/async.c

Lines changed: 22 additions & 38 deletions
Original file line numberDiff line numberDiff line change
@@ -350,12 +350,12 @@ static volatile sig_atomic_t notifyInterruptOccurred = 0;
350350
/* True if we've registered an on_shmem_exit cleanup */
351351
staticboolunlistenExitRegistered= false;
352352

353+
/* True if we're currently registered as a listener in asyncQueueControl */
354+
staticboolamRegisteredListener= false;
355+
353356
/* has this backend sent notifications in the current transaction? */
354357
staticboolbackendHasSentNotifications= false;
355358

356-
/* has this backend executed its first LISTEN in the current transaction? */
357-
staticboolbackendHasExecutedInitialListen= false;
358-
359359
/* GUC parameter */
360360
boolTrace_notify= false;
361361

@@ -724,6 +724,7 @@ static void
724724
Async_UnlistenOnExit(intcode,Datumarg)
725725
{
726726
Exec_UnlistenAllCommit();
727+
asyncQueueUnregister();
727728
}
728729

729730
/*
@@ -768,8 +769,6 @@ PreCommit_Notify(void)
768769
if (Trace_notify)
769770
elog(DEBUG1,"PreCommit_Notify");
770771

771-
Assert(backendHasExecutedInitialListen== false);
772-
773772
/* Preflight for any pending listen/unlisten actions */
774773
foreach(p,pendingActions)
775774
{
@@ -892,11 +891,9 @@ AtCommit_Notify(void)
892891
}
893892
}
894893

895-
/*
896-
* If we did an initial LISTEN, listenChannels now has the entry, so we no
897-
* longer need or want the flag to be set.
898-
*/
899-
backendHasExecutedInitialListen= false;
894+
/* If no longer listening to anything, get out of listener array */
895+
if (amRegisteredListener&&listenChannels==NIL)
896+
asyncQueueUnregister();
900897

901898
/* And clean up */
902899
ClearPendingActionsAndNotifies();
@@ -914,19 +911,12 @@ Exec_ListenPreCommit(void)
914911
* Nothing to do if we are already listening to something, nor if we
915912
* already ran this routine in this transaction.
916913
*/
917-
if (listenChannels!=NIL||backendHasExecutedInitialListen)
914+
if (amRegisteredListener)
918915
return;
919916

920917
if (Trace_notify)
921918
elog(DEBUG1,"Exec_ListenPreCommit(%d)",MyProcPid);
922919

923-
/*
924-
* We need this variable to detect an aborted initial LISTEN. In that case
925-
* we would set up our pointer but not listen on any channel. This flag
926-
* gets cleared in AtCommit_Notify or AtAbort_Notify().
927-
*/
928-
backendHasExecutedInitialListen= true;
929-
930920
/*
931921
* Before registering, make sure we will unlisten before dying. (Note:
932922
* this action does not get undone if we abort later.)
@@ -950,6 +940,9 @@ Exec_ListenPreCommit(void)
950940
QUEUE_BACKEND_PID(MyBackendId)=MyProcPid;
951941
LWLockRelease(AsyncQueueLock);
952942

943+
/* Now we are listed in the global array, so remember we're listening */
944+
amRegisteredListener= true;
945+
953946
/*
954947
* Try to move our pointer forward as far as possible. This will skip over
955948
* already-committed notifications. Still, we could get notifications that
@@ -1022,10 +1015,6 @@ Exec_UnlistenCommit(const char *channel)
10221015
* We do not complain about unlistening something not being listened;
10231016
* should we?
10241017
*/
1025-
1026-
/* If no longer listening to anything, get out of listener array */
1027-
if (listenChannels==NIL)
1028-
asyncQueueUnregister();
10291018
}
10301019

10311020
/*
@@ -1041,8 +1030,6 @@ Exec_UnlistenAllCommit(void)
10411030

10421031
list_free_deep(listenChannels);
10431032
listenChannels=NIL;
1044-
1045-
asyncQueueUnregister();
10461033
}
10471034

10481035
/*
@@ -1160,6 +1147,9 @@ asyncQueueUnregister(void)
11601147

11611148
Assert(listenChannels==NIL);/* else caller error */
11621149

1150+
if (!amRegisteredListener)/* nothing to do */
1151+
return;
1152+
11631153
LWLockAcquire(AsyncQueueLock,LW_SHARED);
11641154
/* check if entry is valid and oldest ... */
11651155
advanceTail= (MyProcPid==QUEUE_BACKEND_PID(MyBackendId))&&
@@ -1168,6 +1158,9 @@ asyncQueueUnregister(void)
11681158
QUEUE_BACKEND_PID(MyBackendId)=InvalidPid;
11691159
LWLockRelease(AsyncQueueLock);
11701160

1161+
/* mark ourselves as no longer listed in the global array */
1162+
amRegisteredListener= false;
1163+
11711164
/* If we were the laziest backend, try to advance the tail pointer */
11721165
if (advanceTail)
11731166
asyncQueueAdvanceTail();
@@ -1524,21 +1517,12 @@ void
15241517
AtAbort_Notify(void)
15251518
{
15261519
/*
1527-
* If we LISTEN but then roll back the transactionwe have set our pointer
1528-
*but havenot made any entry in listenChannels. In that case, remove our
1529-
*pointer again.
1520+
* If we LISTEN but then roll back the transactionafter PreCommit_Notify,
1521+
*we haveregistered as a listener but have not made any entry in
1522+
*listenChannels. In that case, deregister again.
15301523
*/
1531-
if (backendHasExecutedInitialListen)
1532-
{
1533-
/*
1534-
* Checking listenChannels should be redundant but it can't hurt doing
1535-
* it for safety reasons.
1536-
*/
1537-
if (listenChannels==NIL)
1538-
asyncQueueUnregister();
1539-
1540-
backendHasExecutedInitialListen= false;
1541-
}
1524+
if (amRegisteredListener&&listenChannels==NIL)
1525+
asyncQueueUnregister();
15421526

15431527
/* And clean up */
15441528
ClearPendingActionsAndNotifies();

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