public ThreadPoolExecutor getExecutorLazily(ExecutorConfig config) {
    return executorMap.computeIfAbsent(config.getName(), (executorName) -> new Executor(config))
      .getThreadPoolExecutor();
  }
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