[jboss-jira] [JBoss JIRA] (JGRP-1458) SEQUENCER delivers the same message more than once

[David Hotham (JIRA)]

David Hotham created JGRP-1458:
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             Summary: SEQUENCER delivers the same message more than once
                 Key: JGRP-1458
                 URL: https://issues.jboss.org/browse/JGRP-1458
             Project: JGroups
          Issue Type: Bug
    Affects Versions: 3.0.9
            Reporter: David Hotham
            Assignee: Bela Ban


This issue is certainly exposed by my running with a retransmit task in SEQUENCER (per JGRP-1449).  However, I think that it could be hit anyway at a change of view; and I'm sure it's a bug!

In SeqnoTable$Entry.add(seqno), the final branch "seqno > next_to_receive" always returns true.  But it should return the return code from seqnos.add(seqno) (ie, false if the seqno has already been added).

The consequence is that Sequencer's received_table.add() returns true even for a message that has already been delivered, so the message is delivered a second time.


Looking at this code raised another question, for which I should maybe raise a separate ticket.  Let me know if you'd prefer me to do so.

I think that when SeqnoTable.add() creates a new Entry, it always creates Entry(0) (because SeqnoTable.next_to_receive is always 0).  Is that true? and if so, is it correct? 

A might join a group long after some other member B has already broadcast the messages with sequence numbers 0,1,2, say.  Then since A will never receive those messages, isn't it going to end up with an Entry for B in which the Set of seqnos just grows indefinitely?

It looks to me as though maybe when it creates a new entry it should do so with Entry(seqno) rather than Entry(next_to_receive).  Or have I misunderstood something?

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