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commit    44339b892a04e94bbb472235882dc6f7023bdc65
Author:   Robert Haas <rhaas@postgresql.org>
Date:     Mon Jun 06 18:35:30 2016 +0000

    shm_mq: After a send fails with SHM_MQ_DETACHED, later ones should too.
    
    Prior to this patch, it was occasionally possible, after shm_mq_sendv
    had previously returned SHM_MQ_DETACHED, for a later shm_mq_sendv
    operation to fail an assertion instead of just again returning
    SHM_MQ_ATTACHED.  From the shm_mq code's point of view, it was
    expecting to be called again with the same arguments, since the
    previous operation had only partially completed.  However, a caller
    who isn't using non-blocking mode won't be prepared to repeat the call
    with the same arguments, and this code shouldn't expect that they
    will.  Repair in such a way that we'll be OK whether the next call
    uses the same arguments or not.
    
    Found by Andreas Seltenreich.  Analysis and sketch of fix by Amit
    Kapila.  Patch by me, reviewed by Amit Kapila.


 src/backend/storage/ipc/shm_mq.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index 7d1c9cdbd5a..03ca79b5e36 100644
--- a/src/backend/storage/ipc/shm_mq.c
+++ b/src/backend/storage/ipc/shm_mq.c
@@ -366,9 +366,15 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait)
 		res = shm_mq_send_bytes(mqh, sizeof(Size) - mqh->mqh_partial_bytes,
 								((char *) &nbytes) +mqh->mqh_partial_bytes,
 								nowait, &bytes_written);
-		mqh->mqh_partial_bytes += bytes_written;
-		if (res != SHM_MQ_SUCCESS)
+
+		if (res == SHM_MQ_DETACHED)
+		{
+			/* Reset state in case caller tries to send another message. */
+			mqh->mqh_partial_bytes = 0;
+			mqh->mqh_length_word_complete = false;
 			return res;
+		}
+		mqh->mqh_partial_bytes += bytes_written;
 
 		if (mqh->mqh_partial_bytes >= sizeof(Size))
 		{
@@ -378,6 +384,9 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait)
 			mqh->mqh_length_word_complete = true;
 		}
 
+		if (res != SHM_MQ_SUCCESS)
+			return res;
+
 		/* Length word can't be split unless bigger than required alignment. */
 		Assert(mqh->mqh_length_word_complete || sizeof(Size) > MAXIMUM_ALIGNOF);
 	}
@@ -432,7 +441,17 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait)
 						break;
 				}
 			}
+
 			res = shm_mq_send_bytes(mqh, j, tmpbuf, nowait, &bytes_written);
+
+			if (res == SHM_MQ_DETACHED)
+			{
+				/* Reset state in case caller tries to send another message. */
+				mqh->mqh_partial_bytes = 0;
+				mqh->mqh_length_word_complete = false;
+				return res;
+			}
+
 			mqh->mqh_partial_bytes += bytes_written;
 			if (res != SHM_MQ_SUCCESS)
 				return res;
@@ -449,6 +468,15 @@ shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait)
 			chunksize = MAXALIGN_DOWN(chunksize);
 		res = shm_mq_send_bytes(mqh, chunksize, &iov[which_iov].data[offset],
 								nowait, &bytes_written);
+
+		if (res == SHM_MQ_DETACHED)
+		{
+			/* Reset state in case caller tries to send another message. */
+			mqh->mqh_length_word_complete = false;
+			mqh->mqh_partial_bytes = 0;
+			return res;
+		}
+
 		mqh->mqh_partial_bytes += bytes_written;
 		offset += bytes_written;
 		if (res != SHM_MQ_SUCCESS)


[parent: e191a6900520]