我有一个宽度为10的固定线程池ExecutorService,以及一个100 Callable列表,每个等待20秒并记录它们的中断.
我在一个单独的线程中调用该列表中的invokeAll,几乎立即中断该线程. ExecutorService执行按预期中断,但Callables记录的实际中断数远远超过预期10 – 大约20-40.为什么这样,如果ExecutorService可以同时执行不超过10个线程？
完整来源:(由于并发,您可能需要运行一次)
@Test
public void interrupt3() throws Exception{
int callableNum = 100;
int executorThreadNum = 10;
final AtomicInteger interruptCounter = new AtomicInteger(0);
final ExecutorService executorService = Executors.newFixedThreadPool(executorThreadNum);
final List <Callable <Object>> executeds = new ArrayList <Callable <Object>>();
for (int i = 0; i < callableNum; ++i) {
executeds.add(new Waiter(interruptCounter));
}
Thread watcher = new Thread(new Runnable() {
@Override
public void run(){
try {
executorService.invokeAll(executeds);
} catch(InterruptedException ex) {
// NOOP
}
}
});
watcher.start();
Thread.sleep(200);
watcher.interrupt();
Thread.sleep(200);
assertEquals(10,interruptCounter.get());
}
// This class just waits for 20 seconds,recording it's interrupts
private class Waiter implements Callable <Object> {
private AtomicInteger interruptCounter;
public Waiter(AtomicInteger interruptCounter){
this.interruptCounter = interruptCounter;
}
@Override
public Object call() throws Exception{
try {
Thread.sleep(20000);
} catch(InterruptedException ex) {
interruptCounter.getAndIncrement();
}
return null;
}
}
使用WinXP 32位,Oracle JRE 1.6.0_27和JUnit4
解决方法
我不同意你应该只收到10个中断的假设.
Assume the cpu has 1 core. 1. Main thread starts Watcher and sleeps 2. Watcher starts and adds 100 Waiters then blocks 3. Waiter 1-10 start and sleep in sequence 4. Main wakes and interrupts Watcher then sleeps 5. Watcher cancels Waiter 1-5 then is yielded by the OS (now we have 5 interrupts) 6. Waiter 11-13 start and sleep 7. Watcher cancels Waiter 6-20 then is yielded by the OS (now we have 13 interrupts) 8. Waiter 14-20 are "started" resulting in a no-op 9. Waiter 21-24 start and sleep ....
本质上,我的论点是,无法保证Watcher线程在允许生成时间片并允许ExecutorService的工作线程启动更多Waiter任务之前,将允许取消所有100个“Waiter”RunnableFuture实例.
更新：显示来自AbstractExecutorService的代码
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException {
if (tasks == null)
throw new NullPointerException();
List<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
boolean done = false;
try {
for (Callable<T> t : tasks) {
RunnableFuture<T> f = newTaskFor(t);
futures.add(f);
execute(f);
}
for (Future<T> f : futures) {
if (!f.isDone()) {
try {
f.get(); //If interrupted,this is where the InterruptedException will be thrown from
} catch (CancellationException ignore) {
} catch (ExecutionException ignore) {
}
}
}
done = true;
return futures;
} finally {
if (!done)
for (Future<T> f : futures)
f.cancel(true); //Specifying "true" is what allows an interrupt to be sent to the ExecutorService's worker threads
}
}
包含f.cancel(true)的finally块是当中断传播到当前正在运行的任务时.如您所见,这是一个紧凑的循环,但不能保证执行循环的线程能够在一个时间片中遍历Future的所有实例.
