// com.google.common.util.concurrent.MoreExecutors#shutdownAndAwaitTermination

public static boolean shutdownAndAwaitTermination(

    ExecutorService service, long timeout, TimeUnit unit) {

  // 把阻塞时间平分

  long halfTimeoutNanos = unit.toNanos(timeout) / 2;

  // Disable new tasks from being submitted

  // 这一步是必做的，保证线程池不再接受新的任务

  service.shutdown();

  try {

    // Wait for half the duration of the timeout for existing tasks to terminate

    // 先最多等设置的阻塞时间的一半时间

    if (!service.awaitTermination(halfTimeoutNanos, TimeUnit.NANOSECONDS)) {

      // Cancel currently executing tasks

      // 考虑到有些任务可能处于阻塞状态，直接 shutdownNow，会中断执行的任务

      service.shutdownNow();

      // Wait the other half of the timeout for tasks to respond to being cancelled

      service.awaitTermination(halfTimeoutNanos, TimeUnit.NANOSECONDS);

    }

  } catch (InterruptedException ie) {

    // Preserve interrupt status

    Thread.currentThread().interrupt();

    // (Re-)Cancel if current thread also interrupted

    service.shutdownNow();

  }

  return service.isTerminated();

}