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;
}