shm_mq: Repair breakage from previous commit.

robertmhaas · robertmhaas · commit a1480ec1d3ba · 2015-10-22T22:01:11.000-04:00
If the counterparty writes some data into the queue and then detaches,
it's wrong to return SHM_MQ_DETACHED right away.  If we do that, we
fail to read whatever was written.
diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
@@ -501,10 +501,12 @@ shm_mq_receive(shm_mq_handle *mqh, Size *nbytesp, void **datap, bool nowait)
 	{
 		if (nowait)
 		{
-			if (shm_mq_counterparty_gone(mq, mqh->mqh_handle))
-				return SHM_MQ_DETACHED;
 			if (shm_mq_get_sender(mq) == NULL)
+			{
+				if (shm_mq_counterparty_gone(mq, mqh->mqh_handle))
+					return SHM_MQ_DETACHED;
 				return SHM_MQ_WOULD_BLOCK;
+			}
 		}
 		else if (!shm_mq_wait_internal(mq, &mq->mq_sender, mqh->mqh_handle)
 				 && shm_mq_get_sender(mq) == NULL)

Original file line number	Diff line number	Diff line change
`@@ -501,10 +501,12 @@ shm_mq_receive(shm_mq_handle mqh, Size nbytesp, void **datap, bool nowait)`
`501`	`501`	`{`
`502`	`502`	`if (nowait)`
`503`	`503`	`{`
`504`		`- if (shm_mq_counterparty_gone(mq, mqh->mqh_handle))`
`505`		`- return SHM_MQ_DETACHED;`
`506`	`504`	`if (shm_mq_get_sender(mq) == NULL)`
	`505`	`+ {`
	`506`	`+ if (shm_mq_counterparty_gone(mq, mqh->mqh_handle))`
	`507`	`+ return SHM_MQ_DETACHED;`
`507`	`508`	`return SHM_MQ_WOULD_BLOCK;`
	`509`	`+ }`
`508`	`510`	`}`
`509`	`511`	`else if (!shm_mq_wait_internal(mq, &mq->mq_sender, mqh->mqh_handle)`
`510`	`512`	`&& shm_mq_get_sender(mq) == NULL)`