何时使用 Guava sameThreadExecutor

Question

我只是运行变成这样的代码：

ExecutorService executorService = MoreExecutors.sameThreadExecutor();

for (int i = 0; i < 10; i++) {
  executorService.submit(new Callable<Void>() {
    @Override
    public Void call() throws Exception {
      try {
        Do some work here...
        return null;
      } catch (final Exception e) {
        throw e;
      } finally {
        //
      }
    }
  });
}

这和下面的代码片段有什么区别吗？如果我理解正确的话，sameThreadExecutor使用调用submit()的同一个线程，也就是说这10个"jobs"都是在主线程上一个一个运行

for (int i = 0; i < 10; i++) {
      try {
        Do some work here...
      } catch (final Exception e) {
        throw e;
      } finally {
        //
      }
}

谢谢！

Answer 1

首先，MoreExecutors#sameThreadExecutor 已弃用：

Deprecated. Use directExecutor() if you only require an Executor and newDirectExecutorService() if you need a ListeningExecutorService. This method will be removed in August 2016.

所以问题是：什么时候需要 MoreExecutors#directExecutor or MoreExecutors#newDirectExecutorService（上面提到了两者之间的区别 - ListeningExecutorService 是 Guava 对 ListenableFutures 的扩展）。答案是：

在您需要 Executor / ExecutorService（例如您的界面需要它）并且不想要并发而是运行您的多线程代码同步时使用它
（上面暗示）在测试中使用它以获得可预测的结果
当您想自己实现 newDirectExecutorService 之类的简单 ExecutorService，但又不想重新发明轮子时（参见 its source code）
如果您使用 ListenableFuture##addCallback(ListenableFuture, FutureCallback), newDirectExecutorService is used by default ("for use when the callback is fast and lightweight", also mentions it's "a dangerous choice in some cases" (see javadoc)).

何时使用 Guava sameThreadExecutor

When to use Guava sameThreadExecutor

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