public synchronized void cancel(boolean mayInterruptIfRunning) {
    if (isScheduled()) {
      choreService.cancelChore(this, mayInterruptIfRunning);
    }
    choreService = null;
  }
Returns false when the Chore is not currently scheduled with a ChoreService
hbase-common/src/main/java/org/apache/hadoop/hbase/ScheduledChore.java