我需要一次执行一定数量的任务4，就像这样:
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
//...wait for completion somehow
当所有这些都完成后，我如何得到通知?现在我想不出比设置一些全局任务计数器更好的方法，并在每个任务结束时减少它，然后在无限循环中监视这个计数器变成0;或获取一个期货列表，并在无限循环监视器isDone为所有它们。不涉及无限循环的更好的解决方案是什么?
谢谢。
当前回答
这只是我的个人意见。 为了克服CountDownLatch预先知道任务数量的要求，您可以使用简单的Semaphore来使用旧的方式。
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
int numberOfTasks=0;
Semaphore s=new Semaphore(0);
while(...) {
taskExecutor.execute(new MyTask());
numberOfTasks++;
}
try {
s.aquire(numberOfTasks);
...
在任务中调用s.release()就像调用latch.countDown()一样;
其他回答
你可以使用下面的代码:
public class MyTask implements Runnable {
private CountDownLatch countDownLatch;
public MyTask(CountDownLatch countDownLatch {
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
try {
//Do somethings
//
this.countDownLatch.countDown();//important
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
CountDownLatch countDownLatch = new CountDownLatch(NUMBER_OF_TASKS);
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
for (int i = 0; i < NUMBER_OF_TASKS; i++){
taskExecutor.execute(new MyTask(countDownLatch));
}
countDownLatch.await();
System.out.println("Finish tasks");
ExecutorService WORKER_THREAD_POOL
= Executors.newFixedThreadPool(10);
CountDownLatch latch = new CountDownLatch(2);
for (int i = 0; i < 2; i++) {
WORKER_THREAD_POOL.submit(() -> {
try {
// doSomething();
latch.countDown();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
});
}
// wait for the latch to be decremented by the two remaining threads
latch.await();
如果doSomething()抛出一些其他异常，latch.countDown()似乎不会执行，那么我该怎么办?
基本上在ExecutorService上调用shutdown()，然后调用awaitterminate ():
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
taskExecutor.shutdown();
try {
taskExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
} catch (InterruptedException e) {
...
}
你可以把你的任务包装在另一个可运行文件中，它会发送通知:
taskExecutor.execute(new Runnable() {
public void run() {
taskStartedNotification();
new MyTask().run();
taskFinishedNotification();
}
});
您可以使用自己的ExecutorCompletionService子类来包装taskExecutor，并使用自己的BlockingQueue实现在每个任务完成时获得通知，并在完成的任务数量达到预期目标时执行任何回调或其他操作。
