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
在Java8中，你可以用CompletableFuture来实现:
ExecutorService es = Executors.newFixedThreadPool(4);
List<Runnable> tasks = getTasks();
CompletableFuture<?>[] futures = tasks.stream()
.map(task -> CompletableFuture.runAsync(task, es))
.toArray(CompletableFuture[]::new);
CompletableFuture.allOf(futures).join();
es.shutdown();
其他回答
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。
Java 5及以后版本中的CyclicBarrier类就是为这类事情而设计的。
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.invokeAll()为您完成。
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
List<Callable<?>> tasks; // your tasks
// invokeAll() returns when all tasks are complete
List<Future<?>> futures = taskExecutor.invokeAll(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?
