From d74a7e53be060c05990ec9e931242ea8b4eaac16 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Tue, 24 May 2022 10:55:01 -0400 Subject: [PATCH v2] shm_mq_sendv: Fix flushing bug when receiver not yet attached. 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. --- src/backend/storage/ipc/shm_mq.c | 11 +++++------ src/include/storage/shm_mq.h | 1 - 2 files changed, 5 insertions(+), 7 deletions(-) diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c index 6139c622e0..8ca24de8d6 100644 --- a/src/backend/storage/ipc/shm_mq.c +++ b/src/backend/storage/ipc/shm_mq.c @@ -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; } diff --git a/src/include/storage/shm_mq.h b/src/include/storage/shm_mq.h index f5220baa78..b6fe68725d 100644 --- a/src/include/storage/shm_mq.h +++ b/src/include/storage/shm_mq.h @@ -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); -- 2.24.3 (Apple Git-128)