[HBASE-13146] Race Condition in ScheduledChore and ChoreService

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.1.0, 2.0.0
• Fix Version/s: 1.1.0, 2.0.0
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Duo Zhang
• Reporter: Duo Zhang
• Created: 03/Mar/15 14:40
• Updated: 03/Jun/15 15:29
• Resolved: 03/Mar/15 19:32

Description

Here is my findings when addressing HBASE-13145.

ChoreService.java

  public synchronized boolean scheduleChore(ScheduledChore chore) {
      ...
      ScheduledFuture<?> future =
          scheduler.scheduleAtFixedRate(chore, chore.getInitialDelay(), chore.getPeriod(),
            chore.getTimeUnit());
      chore.setChoreServicer(this);
      ...
  }

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

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);
  }

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.

ScheduledChore.java

  public synchronized void cancel(boolean mayInterruptIfRunning) {
    if (isScheduled()) choreServicer.cancelChore(this, mayInterruptIfRunning);

    choreServicer = null;
  }

So if you insert a sleep before cancel(remember to set a larger sleep time here), then you can make the test always fail.