Java ExcutorService優雅關閉方式解析

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

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