[英]How to keep thread waiting in ScheduledExecutorService that has been shutdown
public ScheduledFuture<?> executeTaskWithDelay(String name,
final Runnable runnable, Period delay, boolean isDaemon) {
ScheduledExecutorService executorService =
Executors.newSingleThreadScheduledExecutor(new DefaultThreadFactory(
name, isDaemon));
ScheduledFuture<?> future = executorService.schedule(runnable,
delay.toStandardDuration().getMillis(), TimeUnit.MILLISECONDS);
executorService.shutdown();
return future;
}
当我分析应用程序时,我注意到这个方法创建的调度线程在执行之前总是处于“正在运行”而不是“等待”状态。 如果我删除executorService.shutdown()它会做我想要的(即线程保持等待状态,直到它们运行的时间)。 但是,如果没有executorService.shutdown(),nonDaemon线程在执行后永远不会被垃圾收集。 有没有办法可以确保线程在执行前始终处于等待状态? 或者我可以使用其他替代方法来确保:
线程没有等待因为你没有调用future.get()方法。 我做了一个单元测试来证明这一点。
测试#1(不调用future.get()方法):
@Test
public void testSchedule() throws InterruptedException, ExecutionException {
ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
System.out.println(new Date());
ScheduledFuture<?> future = executorService.schedule(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getId() + " - " + Thread.currentThread().getName() + " - Executing thread...");
}
}, 5, TimeUnit.SECONDS);
//System.out.println("future : " + future.get());
executorService.shutdown();
System.out.println(new Date());
}
输出是:
Thu May 24 10:11:14 BRT 2012
Thu May 24 10:11:14 BRT 2012
测试#2(调用future.get()方法):
@Test
public void testSchedule() throws InterruptedException, ExecutionException {
ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
System.out.println(new Date());
ScheduledFuture<?> future = executorService.schedule(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getId() + " - " + Thread.currentThread().getName() + " - Executing thread...");
}
}, 5, TimeUnit.SECONDS);
System.out.println("future : " + future.get());
executorService.shutdown();
System.out.println(new Date());
}
输出是:
Thu May 24 10:12:48 BRT 2012
8 - pool-1-thread-1 - Executing thread...
future : null
Thu May 24 10:12:53 BRT 2012
我希望它对你有所帮助!
您所看到的是ScheduledExecutor委托给普通的ThreadPoolExecutor以获取关闭功能。 关闭TPE时,其所有线程都会在后备工作队列中旋转,直到它为空。 那么ScheduledThreadPool使用的DelayedQueue可能不是空的,但是如果你进行了轮询,你会得到一个空值,因为任务还没有准备好安排。 它会旋转并旋转直到准备好
你唯一能做的就是shutdownNow并执行以其他方式返回的任务。
我也被告知这实际上是在Java 7中修复的
找出一个解决方案:它是shutdown(),它将所有待处理任务线程的状态从“等待”更改为“正在运行”。 我现在使用executorService来调度自己的shutdown(),而不是立即调用shutdown()。 这可确保挂起的任务尽可能长时间保持等待状态 - 从而节省CPU资源。
public ScheduledFuture<?> executeTaskWithDelay(String name,
final Runnable runnable, Period delay, boolean isDaemon) {
final ScheduledExecutorService executorService =
Executors.newSingleThreadScheduledExecutor(new DefaultThreadFactory(
name, isDaemon));
ScheduledFuture<?> future = executorService.schedule(runnable,
delay.toStandardDuration().getMillis(), TimeUnit.MILLISECONDS);
executorService.schedule(new Runnable() {
@Override
public void run() {
executorService.shutdown();
}}, delay.toStandardDuration().getMillis(), TimeUnit.MILLISECONDS);
return future;
}
跑你的代码。 这是来自jvisualvm中的线程转储(我命名为线程“bla”):
"bla" prio=5 tid=7fa2bc16a000 nid=0x10bd53000 runnable [10bd52000]
java.lang.Thread.State: RUNNABLE
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:950)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:680)
Locked ownable synchronizers:
- None
现在,这是来自于ThreadPoolExecutor.java:950
grepcode:
944 // It is possible (but unlikely) for a thread to have been
945 // added to workers, but not yet started, during transition to
946 // STOP, which could result in a rare missed interrupt,
947 // because Thread.interrupt is not guaranteed to have any effect
948 // on a non-yet-started Thread (see Thread#interrupt).
949 if (runStateOf(ctl.get()) == STOP && ! t.isInterrupted())
950 t.interrupt();
这让我得出结论,问题出在您的测试代码中 - 您正在关闭执行程序太快,并且线程发现自己处于一种奇怪的状态。 这不应该是生产代码中的问题。
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