java - 我们如何知道线程已经完成了它的执行？

Question

我正在使用 ExecutorService。以下是代码

public class A{ 
   public static void main(String args[]){
        ExecutorService executorService = Executors.newFixedThreadPool(5);
        Runnable worker = new FileUploadThread("thread");
        executorService.execute(worker);
   } 
}

public class FileuploadThread extends Thread{
    //has a parametrized constuctor

     @Override
     public void run(){
        for(int i=0; i<10000; i++){
            syso("executing...");
        }
     }
}

当线程完成它的任务时，我想在 main 方法中接收一个事件或其他东西。我怎样才能做到这一点 ？

Answer 1

要了解任务状态 - 您需要 Future 实例。
现在有两点:

如果您只是想知道任务是否已完成，请使用 executorService.submit(worker) , 而不是 executorService.execute(worker)方法。

如果您还想在任务完成后获得一些结果，请使用 Callable接口(interface)而不是 Runnable .见下面的代码:

public class A {
  public static void main(String args[]){
    ExecutorService executorService = Executors.newFixedThreadPool(5);
    Callable<String> worker = new FileUploadThread("thread");
    Future<String> workerTask = executorService.submit(worker);

    try {
        boolean isDone = workerTask.isDone();
        System.out.println("Task is done: " + isDone);

        //Wait untill task is executing
        String status = workerTask.get();

        System.out.println("Status: " + status);
        isDone = workerTask.isDone();
        System.out.println("Task is done: " + isDone);
    } catch (InterruptedException | ExecutionException e) {
        e.printStackTrace();
    }
    executorService.shutdown();
  }
}

class FileUploadThread implements Callable<String> {
  //has a parametrized constuctor
  public FileUploadThread(String thread) { }

  @Override
  public String call() throws Exception {
    for(int i=0; i<5; i++){
        System.out.println("executing..sleep for 1 sec...");
        Thread.sleep(1000);
    }
    return "DONE";
  }
}

输出:

Task is done: false
executing..sleep for 1 sec...
executing..sleep for 1 sec...
executing..sleep for 1 sec...
executing..sleep for 1 sec...
executing..sleep for 1 sec...
Status: DONE
Task is done: true