Java调度线程池ScheduledThreadPoolExecutor不执行问题怎么解决？

本篇内容主要讲解“Java调度线程池ScheduledThreadPoolExecutor不执行问题怎么解决”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Java调度线程池ScheduledThreadPoolExecutor不执行问题怎么解决”吧!

ScheduledThreadPoolExecutor不调度分析

示例程序

在示例程序可以看到当计数器中的计数达到5的时候就会主动抛出一个异常，抛出异常后ScheduledThreadPoolExecutor就不调度了。

public class ScheduledTask {
    private static final AtomicInteger count = new AtomicInteger(0);
    private static final ScheduledThreadPoolExecutor SCHEDULED_TASK = new ScheduledThreadPoolExecutor(
            1, new ThreadFactory() {
        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread(Thread.currentThread().getThreadGroup(), r, "sc-task");
            t.setDaemon(true);
            return t;
        }
    });
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(1);
        SCHEDULED_TASK.scheduleWithFixedDelay(() -> {
            System.out.println(111);
            if (count.get() == 5) {
                throw new IllegalArgumentException("my exception");
            }
            count.incrementAndGet();
        }, 0, 5, TimeUnit.SECONDS);
        latch.await();
    }
}

源码分析

ScheduledThreadPoolExecutor#run

run方法内部首先判断任务是不是周期性的任务，如果不是周期性任务通过ScheduledFutureTask.super.run();执行任务；如果状态是运行中或shutdown，取消任务执行；如果是周期性的任务，通过ScheduledFutureTask.super.runAndReset()执行任务并且重新设置状态，成功了就会执行setNextRunTime设置下次调度的时间，问题就是出现在ScheduledFutureTask.super.runAndReset()，这里执行任务出现了异常，导致结果为false，就不进行下次调度时间设置等

        public void run() {
            boolean periodic = isPeriodic();
            if (!canRunInCurrentRunState(periodic))
                cancel(false);
            else if (!periodic)
                ScheduledFutureTask.super.run();
            else if (ScheduledFutureTask.super.runAndReset()) {
                setNextRunTime();
                reExecutePeriodic(outerTask);
            }
        }

*FutureTask#runAndReset

在线程任务执行过程中抛出异常，然后catch到了异常，最终导致这个方法返回false，然后ScheduledThreadPoolExecutor#run就不设置下次执行时间了，代码c.call(); 抛出异常，跳过ran = true;代码，最终runAndReset返回false。

    protected boolean runAndReset() {
        if (state != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return false;
        boolean ran = false;
        int s = state;
        try {
            Callable<V> c = callable;
            if (c != null && s == NEW) {
                try {
                    c.call(); // don't set result
                    ran = true;
                } catch (Throwable ex) {
                    setException(ex);
                }
            }
        } finally {
            // runner must be non-null until state is settled to
            // prevent concurrent calls to run()
            runner = null;
            // state must be re-read after nulling runner to prevent
            // leaked interrupts
            s = state;
            if (s >= INTERRUPTING)
                handlePossibleCancellationInterrupt(s);
        }
        return ran && s == NEW;
    }

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