我们如何知道线程已完成执行？

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...");
        }
     }
}

我想在线程完成任务时在 main 方法中接收事件或其他内容。我该怎么做？

Answer 1

当你start一个线程yourThread.start()时，系统会启动一个新线程来执行run方法中的操作.您可以简单地打印如下内容：System.out.println("FINISHED " + this.getName()) 在 run 方法的末尾。

PS ：请确保不要将上面的打印放在某些循环中，它应该是 run 方法中的最后一条语句. （ .execute() 方法几乎与 .start() 相同）

Answer 2

你可以使用 yourThread.join().

Answer 3

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返回一些结果，请使用 Callable 界面而不是 Runnable。见以下代码：

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

我们如何知道线程已完成执行？

How do we come to know that the thread has finished its execution?

java

multithreading

java-7