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shm_mq_sendv: Fix flushing bug when receiver not yet attached.

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With the old logic, when the reciever had not yet attached, we would
never call shm_mq_inc_bytes_written(), even if force_flush = true
was specified. That could result in a situation where data that the
sender believes it has sent is never received.

Along the way, remove a useless function prototype for a nonexistent
function from shm_mq.h.

Commit 46846433a03dff4f2e08c8a161e54a842da360d6 introduced these
problems.

Pavan Deolasee, with a few changes by me.

Discussion: https://postgr.es/m/CABOikdPkwtLLCTnzzmpSMXo3QZa2yXq0J7Q61ssdLFAJYrOVvQ@mail.gmail.com
This commit is contained in:
Robert Haas 2022-05-24 10:55:01 -04:00
parent 0a050ee000
commit f5bfba5413
2 changed files with 5 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
src/backend/storage/ipc/shm_mq.c
View File

@ -518,8 +518,7 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait,
/*
* If the counterparty is known to have attached, we can read mq_receiver
* without acquiring the spinlock and assume it isn't NULL. Otherwise,
* more caution is needed.
* without acquiring the spinlock. Otherwise, more caution is needed.
*/
if (mqh->mqh_counterparty_attached)
receiver = mq->mq_receiver;
@ -528,9 +527,8 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait,
SpinLockAcquire(&mq->mq_mutex);
receiver = mq->mq_receiver;
SpinLockRelease(&mq->mq_mutex);
if (receiver == NULL)
return SHM_MQ_SUCCESS;
mqh->mqh_counterparty_attached = true;
if (receiver != NULL)
mqh->mqh_counterparty_attached = true;
}
/*
@ -541,7 +539,8 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait,
if (force_flush || mqh->mqh_send_pending > (mq->mq_ring_size >> 2))
{
shm_mq_inc_bytes_written(mq, mqh->mqh_send_pending);
SetLatch(&receiver->procLatch);
if (receiver != NULL)
SetLatch(&receiver->procLatch);
mqh->mqh_send_pending = 0;
}

1
src/include/storage/shm_mq.h
View File

@ -76,7 +76,6 @@ extern shm_mq_result shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov,
int iovcnt, bool nowait, bool force_flush);
extern shm_mq_result shm_mq_receive(shm_mq_handle *mqh,
Size *nbytesp, void **datap, bool nowait);
extern void shm_mq_flush(shm_mq_handle *mqh);
/* Wait for our counterparty to attach to the queue. */
extern shm_mq_result shm_mq_wait_for_attach(shm_mq_handle *mqh);