Java ExcutorService优雅关闭方式

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