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

你可以在这个Runner类上调用waitTillDone():

Runner runner = Runner.runner(4); // create pool with 4 threads in thread pool

while(...) {
    runner.run(new MyTask()); // here you submit your task
}


runner.waitTillDone(); // and this blocks until all tasks are finished (or failed)


runner.shutdown(); // once you done you can shutdown the runner

在调用shutdown()之前,您可以重用这个类并多次调用waitTillDone(),而且您的代码非常简单。你也不需要预先知道任务的数量。

要使用它,只需将gradle/maven compile 'com.github.matejtymes:javafixes:1.3.1'依赖项添加到你的项目中。

详情请点击这里:

https://github.com/MatejTymes/JavaFixes

其他回答

使用CountDownLatch:

CountDownLatch latch = new CountDownLatch(totalNumberOfTasks);
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
  taskExecutor.execute(new MyTask());
}

try {
  latch.await();
} catch (InterruptedException E) {
   // handle
}

在任务中(在try / finally中附上)

latch.countDown();

这可能会有所帮助

Log.i(LOG_TAG, "shutting down executor...");
executor.shutdown();
while (true) {
                try {
                    Log.i(LOG_TAG, "Waiting for executor to terminate...");
                    if (executor.isTerminated())
                        break;
                    if (executor.awaitTermination(5000, TimeUnit.MILLISECONDS)) {
                        break;
                    }
                } catch (InterruptedException ignored) {}
            }

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) {
  ...
}

Project Loom的AutoCloseable执行器服务上的Try-with-Resources语法

Project Loom试图为Java中的并发能力添加新特性。

其中一个特性是使ExecutorService可自动关闭。这意味着每个ExecutorService实现都将提供一个close方法。这意味着我们可以使用try-with-resources语法自动关闭ExecutorService对象。

executorservice# close方法将阻塞,直到所有提交的任务都完成。使用close代替了调用shutdown & awaitterminate。

自动关闭功能有助于Project Loom将“结构化并发”引入Java。

try (
    ExecutorService executorService = Executors.… ;
) {
    // Submit your `Runnable`/`Callable` tasks to the executor service.
    …
}
// At this point, flow-of-control blocks until all submitted tasks are done/canceled/failed.
// After this point, the executor service will have been automatically shutdown, wia `close` method called by try-with-resources syntax.

有关Project Loom的更多信息,请搜索由Ron Pressler和Project Loom团队的其他人所做的演讲和采访。关注更近期的,如Project Loom的发展。

Project Loom技术的实验版本现在已经可以使用了,它是基于早期的Java 18。