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[broker] Fix issue where Key_Shared consumers could get stuck #10920
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Looks like a race condition between sending messages to the consumer and remove the consumer from the selector?
We have a
synchronized
to protect thereadEntriesComplete
andremoveConsumer
. How can this happen?There was a problem hiding this comment.
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@codelipenghui Perhaps this happens if the messages to be redelivered is in the managed ledger cache. In this case,
are executed and completed synchronously in
PersistentDispatcherMultipleConsumers#removeConsumer()
.pulsar/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentDispatcherMultipleConsumers.java
Lines 184 to 195 in 894d92b
synchronized
protection does not work because all of these methods are executed by the same thread.There was a problem hiding this comment.
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Ok, I think the stack trace here would be like:
removeConsumer()
↓
super.removeConsumer()
↓
readMoreEntries()
(This is what is used to trigger the re-delivery of the messages that were pending on the removed consumer)↓
readEntriesComplete()
↓
sendMessagesToConsumers()
As mentioned, this can select the removed consumer which is still in the selector list.At this point, the
sendMessagesToConsumers()
will fail and the message will stay into thependingAcks
set for that consumer, but, since the consumer was already removed, the redelivery of this message will not happen.I think this change is the correct one.
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Oh, I see. Thanks for the explanation @massakam @merlimat. I missed that
super.removeConsumer()
also get a chance to callreadMoreEntries()
.