Java ExcutorService优雅关闭方式解析

关闭时可使用如下代码

public static void waitUntilTerminate(final ExecutorService executorService, final int timeout) {
    try {
      executorService.shutdown();
      if (!executorService.awaitTermination(timeout, TimeUnit.SECONDS)) { //超时后直接关闭
        executorService.shutdownNow();
      }
    } catch (InterruptedException e) { //awaitTermination 出现中断异常也将触发关闭
      executorService.shutdownNow();
    }
  }

但是实际使用中，可能会出现即使使用了shutdownNow方法，还是无法终止线程的问题，那是因为你的线程无法被中断

shutdownNow方法简单理解就是给在运行的线程发一个中断信号，如果你的线程忽略这个信号，那就无法停下来

举个例子来说明这个问题

public class ShutDownUtilsTest {

  private ExecutorService executorService;

  @Before
  public void init() {
    executorService = Executors.newFixedThreadPool(1);
  }

  @Test
  public void shutDownOKTest() {
    ShutDownUtils.waitUntilTerminate(executorService, 1);

    CommonUtils.sleep(1); //等待线程处理中断
    Assert.assertTrue(executorService.isTerminated());
  }

  @Test
  public void shutDownNowFailTest() {
    executorService.execute(this::canNotStopThread);
    ShutDownUtils.waitUntilTerminate(executorService, 0);

    CommonUtils.sleep(1); //等待线程处理中断
    Assert.assertFalse(executorService.isTerminated());
  }

  @Test
  public void shutDownNowOKTest() {
    executorService.execute(this::stopThread);
    ShutDownUtils.waitUntilTerminate(executorService, 0);

    CommonUtils.sleep(1); //等待线程处理中断
    Assert.assertTrue(executorService.isTerminated());
  }

  private void canNotStopThread() {
    for (long i = 0; i < Long.MAX_VALUE; i++) {
    }
  }

  private void stopThread() {
    for (long i = 0; i < Long.MAX_VALUE && !Thread.currentThread().isInterrupted(); i++) {
    }
  }
}

从上面的测试用例可以看到canNotStopThread无法被shutDownNow终止

然而stopThread可以被正常终止，因为通过Thread.currentThread().isInterrupted()在判断线程是否收到了中断信号

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