java - Java 中这段代码中的 ExecutorService.submit 和 ExecutorService.execute 有什么区别？

Question

我正在学习使用 ExectorService 来汇集 threads 并发送任务。我下面有一个简单的程序

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;


class Processor implements Runnable {

    private int id;

    public Processor(int id) {
        this.id = id;
    }

    public void run() {
        System.out.println("Starting: " + id);

        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            System.out.println("sorry, being interupted, good bye!");
            System.out.println("Interrupted " + Thread.currentThread().getName());
            e.printStackTrace();
        }

        System.out.println("Completed: " + id);
    }
}


public class ExecutorExample {

    public static void main(String[] args) {
        Boolean isCompleted = false;

        ExecutorService executor = Executors.newFixedThreadPool(2);

        for (int i = 0; i < 5; i++) {
            executor.execute(new Processor(i));
        }

        //executor does not accept any more tasks but the submitted tasks continue
        executor.shutdown();

        System.out.println("All tasks submitted.");

        try {
            //wait for the exectutor to terminate normally, which will return true
            //if timeout happens, returns false, but this does NOT interrupt the threads
            isCompleted = executor.awaitTermination(100, TimeUnit.SECONDS);
            //this will interrupt thread it manages. catch the interrupted exception in the threads
            //If not, threads will run forever and executor will never be able to shutdown.
            executor.shutdownNow();
        } catch (InterruptedException e) {
        }

        if (isCompleted) {
            System.out.println("All tasks completed.");
        } else {
            System.out.println("Timeout " + Thread.currentThread().getName());
        }
    }
}

它没有什么花哨的，而是创建了两个线程，一共提交了5个任务。在每个 thread 完成其任务后，它会执行下一个任务，在上面的代码中，我使用了 executor.submit。我也改成了executor.execute。但我看不出输出有什么不同。 submit 和 execute 方法有何不同？这就是 API 所说的

Method submit extends base method Executor.execute(java.lang.Runnable) by creating and returning a Future that can be used to cancel execution and/or wait for completion. Methods invokeAny and invokeAll perform the most commonly useful forms of bulk execution, executing a collection of tasks and then waiting for at least one, or all, to complete. (Class ExecutorCompletionService can be used to write customized variants of these methods.)

但我不清楚它的确切含义是什么？

Answer 1

正如您从 JavaDoc execute(Runnable) 中看到的那样不返回任何东西。

但是，submit(Callable<T>)返回 Future对象，它允许您稍后以编程方式取消正在运行的线程并获取 T当 Callable 时返回完成。见 JavaDoc of Future了解更多

Future<?> future = executor.submit(longRunningJob);
...
//long running job is taking too long
future.cancel(true);

此外，如果 future.get() == null并且不抛出任何异常然后 Runnable 成功执行