java - 从 ScheduledExecutorService 停止和删除任务

Question

我知道我可以抛出异常来禁止进一步执行已安排在 ScheduledExecutorService 中重复执行的任务(请参阅 this question)。

我也知道我可以 setRemoveOnCancelPolicy(true) 来确保已取消的任务从队列中移除。

我的问题是:当我从其中抛出异常时，任务是否真的从调度程序中删除了？这是否通过隐式取消 future 发生？如果是，这是否意味着 setRemoveOnCancelPolicy() 也适用于这种情况？

在 Javadocs 中找不到任何内容。

Answer 1

我也有同样的疑问，在文档中找不到任何内容，所以我试了一下。观察:

• 抛出 RuntimeException 将 future 标记为完成，未取消。
• Runnable 从调度程序的队列中删除，不管 setRemoveOnCancelPolicy()。

亲自尝试一下:

public class SchedulerTest {
    protected final Logger log = LoggerFactory.getLogger(this.getClass());

    @Test
    public void schedulerExecutionException() throws Exception {
        log.info("Test: schedulerExecutionException");

        ScheduledThreadPoolExecutor sched = new ScheduledThreadPoolExecutor(2);
        sched.setRemoveOnCancelPolicy(true);

        ScheduledFuture future1 = sched.scheduleAtFixedRate(new Runnable() {
            int counter = 0;
            @Override
            public void run() {
                log.info("Runnable 1: "+ ++counter);

                if (counter >= 2) {
                    log.info("Runnable 1: BOOOM");
                    throw new RuntimeException("boom");
                }

            }
        }, 1, 1, TimeUnit.SECONDS);

        ScheduledFuture future2 = sched.scheduleAtFixedRate(new Runnable() {
            int counter = 0;
            @Override
            public void run() {
                log.info("Runnable 2: "+ ++counter);
            }
        }, 1, 1, TimeUnit.SECONDS);

        long cutoff = new Date().getTime() + 6000;

        while (new Date().getTime() < cutoff) {
            log.info("Scheduler Queue size: "+ sched.getQueue().size());
            log.info("Future 1: is "+ (future1.isCancelled() ? "" : "not ") +"cancelled, is "+ (future1.isDone()? "" : "not ") +"done");
            log.info("Future 2: is "+ (future2.isCancelled() ? "" : "not ") +"cancelled, is "+ (future2.isDone()? "" : "not ") +"done");
            Thread.sleep(1000);
        }
        assertEquals(sched.getQueue().size(), 1);

        future2.cancel(true);
        log.info("Scheduler Queue size: "+ sched.getQueue().size());
        log.info("Future 1: is "+ (future1.isCancelled() ? "" : "not ") +"cancelled, is "+ (future1.isDone()? "" : "not ") +"done");
        log.info("Future 2: is "+ (future2.isCancelled() ? "" : "not ") +"cancelled, is "+ (future2.isDone()? "" : "not ") +"done");

        assertEquals(sched.getQueue().size(), 0);

        sched.shutdownNow();
    }
}