[jira] [Commented] (HBASE-13146) Race Condition in ScheduledChore and ChoreService

["Sean Busbey (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-13146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14345152#comment-14345152 ] 

Sean Busbey commented on HBASE-13146:
-------------------------------------

good find!

> 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
>
>
> 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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