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

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();

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);

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();
  }
});

只是在这里提供更多不同于使用闩锁/屏障的选择。 你也可以在它们全部使用完CompletionService之前得到部分结果。

来自Java并发实践: “如果您有一批计算要提交给Executor,并且您希望检索它们的结果 可用时,您可以保留与每个任务关联的Future,并通过调用get来重复轮询完成 超时为0。这是可能的,但很乏味。幸运的是,还有更好的方法:完井服务。”

这里是实现

public class TaskSubmiter {
    private final ExecutorService executor;
    TaskSubmiter(ExecutorService executor) { this.executor = executor; }
    void doSomethingLarge(AnySourceClass source) {
        final List<InterestedResult> info = doPartialAsyncProcess(source);
        CompletionService<PartialResult> completionService = new ExecutorCompletionService<PartialResult>(executor);
        for (final InterestedResult interestedResultItem : info)
            completionService.submit(new Callable<PartialResult>() {
                public PartialResult call() {
                    return InterestedResult.doAnOperationToGetPartialResult();
                }
        });

    try {
        for (int t = 0, n = info.size(); t < n; t++) {
            Future<PartialResult> f = completionService.take();
            PartialResult PartialResult = f.get();
            processThisSegment(PartialResult);
            }
        } 
        catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        } 
        catch (ExecutionException e) {
            throw somethinghrowable(e.getCause());
        }
    }
}

这是我的解决方案,基于“亚当·天行者”的技巧,它很有效

package frss.main;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestHilos {

    void procesar() {
        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();

        System.out.println("FIN DEL PROCESO DE HILOS");
    }

    private List<Runnable> getTasks() {
        List<Runnable> tasks = new ArrayList<Runnable>();

        Hilo01 task1 = new Hilo01();
        tasks.add(task1);

        Hilo02 task2 = new Hilo02();
        tasks.add(task2);
        return tasks;
    }

    private class Hilo01 extends Thread {

        @Override
        public void run() {
            System.out.println("HILO 1");
        }

    }

    private class Hilo02 extends Thread {

        @Override
        public void run() {
            try {
                sleep(2000);
            }
            catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("HILO 2");
        }

    }


    public static void main(String[] args) {
        TestHilos test = new TestHilos();
        test.procesar();
    }
}