public void submit(final EventHandler eh) {
    Executor executor = getExecutor(eh.getEventType().getExecutorServiceType());
    if (executor == null) {
      // This happens only when events are submitted after shutdown() was
      // called, so dropping them should be "ok" since it means we're
      // shutting down.
      LOG.error("Cannot submit [" + eh + "] because the executor is missing."
        + " Is this process shutting down?");
    } else {
      executor.submit(eh);
    }
  }
Initialize the executor lazily, Note if an executor need to be initialized lazily, then all
paths should use this method to get the executor, should not start executor by using
{@link ExecutorService#startExecutorService(ExecutorConfig)}
hbase-server/src/main/java/org/apache/hadoop/hbase/executor/ExecutorService.java