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Fix attach-related race condition in shm_mq_send_bytes.

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Spotted by Antonin Houska.
This commit is contained in:
Robert Haas 2015-08-07 09:04:07 -05:00
parent 4eda0a6470
commit 846f8c9483
1 changed files with 21 additions and 17 deletions
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38
src/backend/storage/ipc/shm_mq.c
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@ -777,33 +777,37 @@ shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, const void *data,
return SHM_MQ_DETACHED; return SHM_MQ_DETACHED;
} }
if (available == 0) if (available == 0 && !mqh->mqh_counterparty_attached)
{ {
shm_mq_result res;
/* /*
* The queue is full, so if the receiver isn't yet known to be * The queue is full, so if the receiver isn't yet known to be
* attached, we must wait for that to happen. * attached, we must wait for that to happen.
*/ */
if (!mqh->mqh_counterparty_attached) if (nowait)
{ {
if (nowait) if (shm_mq_get_receiver(mq) == NULL)
{ {
if (shm_mq_get_receiver(mq) == NULL)
{
*bytes_written = sent;
return SHM_MQ_WOULD_BLOCK;
}
}
else if (!shm_mq_wait_internal(mq, &mq->mq_receiver,
mqh->mqh_handle))
{
mq->mq_detached = true;
*bytes_written = sent; *bytes_written = sent;
return SHM_MQ_DETACHED; return SHM_MQ_WOULD_BLOCK;
} }
mqh->mqh_counterparty_attached = true;
} }
else if (!shm_mq_wait_internal(mq, &mq->mq_receiver,
mqh->mqh_handle))
{
mq->mq_detached = true;
*bytes_written = sent;
return SHM_MQ_DETACHED;
}
mqh->mqh_counterparty_attached = true;
/*
* The receiver may have read some data after attaching, so we
* must not wait without rechecking the queue state.
*/
}
else if (available == 0)
{
shm_mq_result res;
/* Let the receiver know that we need them to read some data. */ /* Let the receiver know that we need them to read some data. */
res = shm_mq_notify_receiver(mq); res = shm_mq_notify_receiver(mq);