@Override
  public void start() {
    LOG.info("Using {} as user call queue; handlerCount={}; maxQueueLength={}",
      this.getClass().getSimpleName(), handlerCount, maxQueueLength);
    this.executor = new ThreadPoolExecutor(handlerCount, handlerCount, 60, TimeUnit.SECONDS,
      new ArrayBlockingQueue<>(maxQueueLength),
      new ThreadFactoryBuilder().setNameFormat("FifoRpcScheduler.handler-pool-%d").setDaemon(true)
        .setUncaughtExceptionHandler(Threads.LOGGING_EXCEPTION_HANDLER).build(),
      new ThreadPoolExecutor.CallerRunsPolicy());
  }
A very simple {@code }RpcScheduler} that serves incoming requests in order. This can be used for
HMaster, where no prioritization is needed.
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/FifoRpcScheduler.java