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Fix attach-related race condition in shm_mq_send_bytes.

Spotted by Antonin Houska.

1 parent4eda0a6 commit846f8c9Copy full SHA for 846f8c9

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+21

-17

lines changed

src/backend/storage/ipc
- shm_mq.c

1 file changed

+21

-17

lines changed

`‎src/backend/storage/ipc/shm_mq.c`

Lines changed: 21 additions & 17 deletions

Original file line number	Diff line number	Diff line change
`@@ -777,33 +777,37 @@ shm_mq_send_bytes(shm_mq_handle mqh, Size nbytes, const void data,`
`777`	`777`	`returnSHM_MQ_DETACHED;`
`778`	`778`	`}`
`779`	`779`
`780`		`-if (available==0)`
	`780`	`+if (available==0&& !mqh->mqh_counterparty_attached)`
`781`	`781`	`{`
`782`		`-shm_mq_resultres;`
`783`		`-`
`784`	`782`	`/*`
`785`	`783`	`* The queue is full, so if the receiver isn't yet known to be`
`786`	`784`	`* attached, we must wait for that to happen.`
`787`	`785`	`*/`
`788`		`-if (!mqh->mqh_counterparty_attached)`
	`786`	`+if (nowait)`
`789`	`787`	`{`
`790`		`-if (nowait)`
	`788`	`+if (shm_mq_get_receiver(mq)==NULL)`
`791`	`789`	`{`
`792`		`-if (shm_mq_get_receiver(mq)==NULL)`
`793`		`-{`
`794`		`-*bytes_written=sent;`
`795`		`-returnSHM_MQ_WOULD_BLOCK;`
`796`		`-}`
`797`		`-}`
`798`		`-elseif (!shm_mq_wait_internal(mq,&mq->mq_receiver,`
`799`		`-mqh->mqh_handle))`
`800`		`-{`
`801`		`-mq->mq_detached= true;`
`802`	`790`	`*bytes_written=sent;`
`803`		`-returnSHM_MQ_DETACHED;`
	`791`	`+returnSHM_MQ_WOULD_BLOCK;`
`804`	`792`	`}`
`805`		`-mqh->mqh_counterparty_attached= true;`
`806`	`793`	`}`
	`794`	`+elseif (!shm_mq_wait_internal(mq,&mq->mq_receiver,`
	`795`	`+mqh->mqh_handle))`
	`796`	`+{`
	`797`	`+mq->mq_detached= true;`
	`798`	`+*bytes_written=sent;`
	`799`	`+returnSHM_MQ_DETACHED;`
	`800`	`+}`
	`801`	`+mqh->mqh_counterparty_attached= true;`
	`802`	`+`
	`803`	`+/*`
	`804`	`+ * The receiver may have read some data after attaching, so we`
	`805`	`+ * must not wait without rechecking the queue state.`
	`806`	`+ */`
	`807`	`+}`
	`808`	`+elseif (available==0)`
	`809`	`+{`
	`810`	`+shm_mq_resultres;`
`807`	`811`
`808`	`812`	`/* Let the receiver know that we need them to read some data. */`
`809`	`813`	`res=shm_mq_notify_receiver(mq);`

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Commit846f8c9

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1 file changed

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`‎src/backend/storage/ipc/shm_mq.c`

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