[FIXED] Possible race causing ack'ed message to be redelivered #1139
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During redelivery, a go routine gathers all pending messages under a lock. However, the actual send of messages is done one by one and by then, one of the message in the list of messages to redeliver may have been acknowledged. So during the send, under the sub's lock, we need to check that if a message marked as redelivered is no longer in the pending list, it should not be sent to the client. Also fixed an unrelated data race that was just found running tests. Resolves #1138 Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
server/server.go
Outdated
| @@ -3721,23 +3730,28 @@ func (s *StanServer) performAckExpirationRedelivery(sub *subState, isStartup boo | |||
| // otherwise this could cause a message to be redelivered to multiple members. | |||
| if !isClustered && qs != nil && !isStartup { | |||
| qs.Lock() | |||
| sub.Lock() | |||
| skip := !sub.isMsgStillPending(m) | |||
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very minor nitpick, take it or leave it, but could use msgPending := sub.isMsgStillPending(m) and avoid the !s. It might read easier.
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Will do, and actually should not try to send if not pending.. so thanks!
Used code review recommendation and fixed the queue case. Added queue sub in new test that would have caught the bug. Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
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During redelivery, a go routine gathers all pending messages under
a lock. However, the actual send of messages is done one by one
and by then, one of the message in the list of messages to redeliver
may have been acknowledged. So during the send, under the sub's lock,
we need to check that if a message marked as redelivered is no longer
in the pending list, it should not be sent to the client.
Also fixed an unrelated data race that was just found running tests.
Resolves #1138
Signed-off-by: Ivan Kozlovic ivan@synadia.com