[jboss-jira] [JBoss JIRA] (JGRP-1495) SEQUENCER delivers messages and views out of order

[David Hotham (JIRA)]

     [ https://issues.jboss.org/browse/JGRP-1495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

David Hotham updated JGRP-1495:
-------------------------------

    Summary: SEQUENCER delivers messages and views out of order  (was: SEQUENCER needs a lock for delivery of messages)

    
> SEQUENCER delivers messages and views out of order
> --------------------------------------------------
>
>                 Key: JGRP-1495
>                 URL: https://issues.jboss.org/browse/JGRP-1495
>             Project: JGroups
>          Issue Type: Feature Request
>    Affects Versions: 3.1
>            Reporter: David Hotham
>            Assignee: Bela Ban
>
> I first raised this, or something very like it, in JGRP-1468; but it got lost among the other fixes that were made in that issue.
> I've just seen a case where after a merge-view the following happens at a node W:
> {noformat}
>           SEQUENCER            GMS            APPLICATION
>              |                  |                  |
>  B (view)    |                  |                  |
> ------------>|                  |                  |
>              |----------------->|                  |
>              |                  |----\             |
>  C (view)    |                  |     \            |
> ------------>|                  |      \           |
>              |----------------->|       \          |
>              |                  |        \         |
>  C (msg)     |                  |        |         |
> ------------>|                  |        |         |
>              |---------------------------|-------->|
>              |                  |        |         |
>              |                  |        \         |
>              |                  |         \------->|
> {noformat}
> -  Initially the view is {B,W}
> -  There's a merge view, in which B and C were the old coordinators
> -  B and C both broadcast the new view {B,C,T,W}.  In fact both know the physical address of the member shown above (or we're using UDP multicast, if you like); so the view is sent to this node twice.
> -  B's view arrives on thread Incoming-1, and gets as far as GMS
> -  C's view arrives on thread Incoming-2, and gets as far as GMS (where it is dropped, since it is the same view)
> -  A message from C, prompted by the change in view, arrives on thread Incoming-2
> -  This overtakes the view on thread Incoming-1, and is delivered to the application
> -  Only then does thread Incoming-1 get to deliver the view to the application
> ie from the application's point of view: C broadcast the view and then the message; whereas at the node shown above the application received the message and then the view.
> I think that the fix will simply be to put a lock in SEQUENCER around up_prot.up(evt) in SEQUENCER.deliver().  That way messages will be delivered to the application in the same order as they arrive at SEQUENCER.  
> Edit: updated description for clarity

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