Allow interrupting GetMultiXactIdMembers

alvherre · alvherre · commit 137e4da6df75 · 2014-11-14T15:14:02.000-03:00
This function has a loop which can lead to uninterruptible process
"stalls" (actually infinite loops) when some bugs are triggered.  Avoid
that unpleasant situation by adding a check for interrupts in a place
that shouldn't degrade performance in the normal case.

Backpatch to 9.3.  Older branches have an identical loop here, but the
aforementioned bugs are only a problem starting in 9.3 so there doesn't
seem to be any point in backpatching any further.
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
@@ -1258,6 +1258,7 @@ GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
 		{
 			/* Corner case 2: next multixact is still being filled in */
 			LWLockRelease(MultiXactOffsetControlLock);
+			CHECK_FOR_INTERRUPTS();
 			pg_usleep(1000L);
 			goto retry;
 		}

Original file line number	Diff line number	Diff line change
`@@ -1258,6 +1258,7 @@ GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,`
`1258`	`1258`	`{`
`1259`	`1259`	`/* Corner case 2: next multixact is still being filled in */`
`1260`	`1260`	`LWLockRelease(MultiXactOffsetControlLock);`
	`1261`	`+ CHECK_FOR_INTERRUPTS();`
`1261`	`1262`	`pg_usleep(1000L);`
`1262`	`1263`	`goto retry;`
`1263`	`1264`	`}`