等待執行程序服務線程

Question

我有一個類，它使用executor服務來同時運行任務。

代碼：

class SomeClass{ 
private static ExecutorService taskThread = Executors.newFixedThreadPool(1, new ThreadFactory() { 
     private int threadCount = 0; 

     @Override 
     public Thread newThread(Runnable r) { 
      Thread t = new Thread(r); 
      t.setDaemon(true); 
      return t; 
     } 
    }); 

    static { 
     Runtime.getRuntime().addShutdownHook(new Thread() { 
      @Override 
      public void run() { 
       // TODO Auto-generated method stub 
       taskThread.shutdown(); 
      } 
     }); 
    } 


doSomeTask() 
{ 
      DocumentUploader callable = new DocumentUploader(randomID,fileLoc);   
      FutureTask<String> task1 = new FutureTask<String>(callable); 
      taskThread.execute(task1); 
} 


someFunctionforWait(){ 


//what here..??? 
} 

我還有一個類名SomeOtherClass將訪問由task1線程完成的修改/計算。所以我需要等待線程完成，那麼我如何等待task1完成。我打算做的是致電SomeOtherClasssomeFunctionforWait()檢查線程是否已完成，然後開始執行任務。

我該怎麼做。

Answer 1

創建Future到taskThread並調用get()就可以了。它會阻止，直到Future完成：

Future<String> f = taskThread.submit(callable); // concurrent operation 
String result = f.get(); // blocks until f completes 
// use result 

Answer 2

你可以使用期貨，或者如果你想堅持使用ExecutorService的，只是等待taskThread.shutdown（）和taskThread.awaitTermination（）;你可以把這些語句放到你的someFunctionforWait（）中，然後繼續執行。這是基於你的代碼一個簡單的例子：

public class SomeClass { 
    private ExecutorService taskThread = Executors.newFixedThreadPool(1); 
    private List<Future<String>> futures = new ArrayList<Future<String>>(); 
    void doSomeTask() { 
     FutureTask<String> task1 = new FutureTask<String>(new Callable<String>() { 
      public String call() throws Exception { 
       System.out.println("thread executing"); 
       Thread.sleep(1000); 
       return Thread.currentThread().toString(); 
      } 
     }); 
     taskThread.execute(task1); 
     futures.add(task1); 
    }; 

    public void someFunctionforWait() throws InterruptedException, ExecutionException{ 
     taskThread.shutdown(); 
     taskThread.awaitTermination(5, TimeUnit.SECONDS); 
     System.out.println("joined"); 
    } 

    public void someFunctionforWaitAlternative() throws InterruptedException, ExecutionException{ 
     for(Future<String> future : futures) { 
      System.out.println("future val: " + future.get()); 
     } 
     System.out.println("joined"); 
    } 

    public static void main(String[] args) throws Exception { 
     SomeClass c = new SomeClass(); 
     c.doSomeTask(); 
     c.someFunctionforWait(); 
     //c.someFunctionforWaitAlternative(); 
    } 
}