[jboss-jira] [JBoss JIRA] Created: (JGRP-986) FLUSH: relax event sequencing for a joining member

[Vladimir Blagojevic (JIRA)]

FLUSH: relax event sequencing for a joining member
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                 Key: JGRP-986
                 URL: https://jira.jboss.org/jira/browse/JGRP-986
             Project: JGroups
          Issue Type: Bug
    Affects Versions: 2.6.10, 2.8
            Reporter: Vladimir Blagojevic
            Assignee: Vladimir Blagojevic
             Fix For: 2.6.11, 2.8


There is a possibility that a message could get dropped for a joining member C as it joins a cluster (and it should not get dropped). Flush has a latch (allowMessagesToPassUp) that is turned on once a joining member C receives a first stop flush - received right after a first view, sent from coordinator, say member A. If a message M from another member B happens to go up the stack before first stop flush reaches C - member C drops message M. This latch was introduced to always enforce a strict order between view, unblock and message M. 

If we did not have this switch then we could have reverse order of unblock and a message M, that is messages could go up the stack before unblock. Note that this does not violate virtual synchrony in any way - messages are still received after the first view. However, we need to document unblock callback to clearly make a note of this.

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