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From "Jonathan Lawlor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13146) Race Condition in ScheduledChore and ChoreService
Date Tue, 03 Mar 2015 17:46:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14345396#comment-14345396
] 

Jonathan Lawlor commented on HBASE-13146:
-----------------------------------------

Thanks for digging in here [~Apache9] and catching my mistake. This is a great find and the
change makes sense to me.

> Race Condition in ScheduledChore and ChoreService
> -------------------------------------------------
>
>                 Key: HBASE-13146
>                 URL: https://issues.apache.org/jira/browse/HBASE-13146
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 2.0.0, 1.1.0
>            Reporter: zhangduo
>            Assignee: zhangduo
>             Fix For: 2.0.0, 1.1.0
>
>         Attachments: HBASE-13146.patch
>
>
> Here is my findings when addressing HBASE-13145.
> {code:title=ChoreService.java}
>   public synchronized boolean scheduleChore(ScheduledChore chore) {
>       ...
>       ScheduledFuture<?> future =
>           scheduler.scheduleAtFixedRate(chore, chore.getInitialDelay(), chore.getPeriod(),
>             chore.getTimeUnit());
>       chore.setChoreServicer(this);
>       ...
>   }
> {code}
> So we schedule the chore first, and then set chore servicer. And for CompactionChecker,
the initialDelay is 0, so it is possible that the chore is run before we set chore servicer
for it. And see this
> {code:title=ScheduledChore.java}
>   public void run() {
>     ...
>     else if (stopper.isStopped() || !isScheduled()) {
>       cancel(false);
>       cleanup();
>       if (LOG.isInfoEnabled()) LOG.info("Chore: " + getName() + " was stopped");
>     }
>     ...
>   }
>     ...
>   public synchronized boolean isScheduled() {
>     return choreServicer != null && choreServicer.isChoreScheduled(this);
>   }
> {code}
> So it is possible that isScheduled() returns false and we start to cancel the chore.
You can insert a sleep between scheduled chore and set chore servicer, then you can always
get the log ' Chore: CompactionChecker was stopped'. But it does not always actually cancel
the chore because the cancel method's implementation.
> {code:title=ScheduledChore.java}
>   public synchronized void cancel(boolean mayInterruptIfRunning) {
>     if (isScheduled()) choreServicer.cancelChore(this, mayInterruptIfRunning);
>     choreServicer = null;
>   }
> {code}
> So if you insert a sleep before cancel(remember to set a larger sleep time here), then
you can make the test always fail.



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