[jboss-jira] [JBoss JIRA] (JGRP-1377) Merge: add second line of defense for killing of runaway merge tasks

[Bela Ban (Created) (JIRA)]

Merge: add second line of defense for killing of runaway merge tasks
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                 Key: JGRP-1377
                 URL: https://issues.jboss.org/browse/JGRP-1377
             Project: JGroups
          Issue Type: Task
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.0


This prevents the following scenario:
- A merge ID is set and the merge task started
- If the merge task ends without setting merge-id back to null, subsequent merge requests will be rejected, because the merge coordinator thinks there is a merge still ongoing
- This should not happen, but I nevertheless want to add a second line of defense to prevent this

SOLUTION:
- Whenever a merge-id is assigned and the merge task started, we also keep track of the time this happened
- A separate timer task is started and runs every (say) M seconds (e.g. 2 minutes)
- The task checks whether the time stamp of the last merge (if not 0 (= no merge is running)) is more than N seconds old 
- (M and N are configurable)
- If this is the case, then we force-cancel the merge
- The forceCancelMerge() operation is also exposed via JMX, so it can be invoked (e.g.) across a cluster: probe.sh op=GMS.forceCancelMerge


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