@Override
  public boolean hasRunnables() {
    schedLock();
    try {
      return queueHasRunnables();
    } finally {
      schedUnlock();
    }
  }
Returns true if there are procedures available to process. NOTE: this method is called with the
sched lock held.
@return true if there are procedures available to process, otherwise false.
hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/AbstractProcedureScheduler.java