Java ExcutorService優雅關閉方式

關閉時可使用如下代碼

public static void waitUntilTerminate(final ExecutorService executorService, final int timeout) {
        try {
            executorService.shutdown();
            if (!executorService.awaitTermination(timeout, TimeUnit.SECONDS)) { //超時后直接關閉
                executorService.shutdownNow();
            }
        } catch (InterruptedException e) { //awaitTermination 出現中斷異常也將觸發關閉
            executorService.shutdownNow();
        }
    }

但是實際使用中，可能會出現即使使用了shutdownNow方法，還是無法終止線程的問題，那是因為你的線程無法被中斷

shutdownNow方法簡單理解就是給在運行的線程發一個中斷信號，如果你的線程忽略這個信號，那就無法停下來

舉個例子來說明這個問題

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); //等待線程處理中斷
        Assert.assertTrue(executorService.isTerminated());
    }

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

        CommonUtils.sleep(1); //等待線程處理中斷
        Assert.assertFalse(executorService.isTerminated());
    }

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

        CommonUtils.sleep(1); //等待線程處理中斷
        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++) {
        }
    }
}

從上面的測試用例可以看到canNotStopThread無法被shutDownNow終止

然而stopThread可以被正常終止，因為通過Thread.currentThread().isInterrupted()在判斷線程是否收到了中斷信號