Java Pause Execution

Question

I have a pool of threads which are working independently. Basically these threads are getting data from websites. I have also another thread which change my System IP. I just need to pause all other threads while another thread is changing ip. As soon as ip will change then other threads pool will resume.

Is there any solution?

Here is my Code:

for(;;){
  for (int aa = 0; aa < pages.size(); aa++) {
    if (pageID != null) {
      t = new Thread(new BackgroundThread(pageID.get(aa)));
      System.out.println(pageID.get(aa));
      t.start();
    }
    if(ipNo == 3){
      ipNo = 0;
    }
    if(aa == 35) {
      //Following method take a little bit time to change ip. I need when this method will be executin then 
      //all above threads "t" will be paused
      IPRotator.rotateIP(ip[ipNo]); 
      //When IP will be change then all paused threads will be resumed
      ipNo++;
    }
  }
}

I think you are doing something illegal here :) Anyway - do threads have while(true) in them? Show some code. — Bozho
– Bozho, Commented Jul 3, 2010 at 21:13
Think positive Be Positve!! I am changing my NIC IP not illegal stuff!!! ;-) — Novice
– Novice, Commented Jul 3, 2010 at 21:25
@Bozho, unless the question is along the lines of "How to I break the law?" I don't think we can assume anyone is doing anything illegal. — Dolph
– Dolph, Commented Jul 3, 2010 at 22:01

mdma · Accepted Answer · 2010-07-03 21:31:54Z

I'm assuming you really mean you are changing the machine IP? You need to be sure that the threads are in a state where the system IP can be changed, and also that the system IP changer needs to wait until all threads are pausing for the IP to be changed.

This can be done using a CountDownLatch to indicate that threads should pause - each thread counts down the latch. When all threads have hit the latch, the system IP updater can proceed. Once it's done it's work, it then resumes the threads by setting the latch to null.

Exception handling omitted for clarity.

  class SystemIPChanger implements Runnable {
      Collection<WorkerThread> pool;

      public void changeIP() {
          pauseAllThreads();
          changeIP();
          resumeThreads();
      }

      void pauseAllThreads() {
          CountDownLatch latch = new CountDownLatch(pool.size());
          for (WorkerThread worker : pool) {
              worker.setPause(latch);
          }
          latch.await();          
      }

      void resumeThreads() {
          for (WorkerThread worker : pool) {
              worker.setPause(null);
          }

      }
  }

  class WorkerThread implements Runnable {
    private CountDownLatch pause;

    public void run() {
        while (...) {
            pause();
            doRealWork(); 
        }
    }


    synchronized void pause() {
        CountdownLatch latch = pause;
        if (latch!=null) {
           latch.countDown();
           while (pause==latch) {
               wait();
           }
        }
    }

    public synchronized void setPause(CountDownLatch latch) {
        this.pause = latch;
        notifyAll();
    }
  }

pdbartlett · Accepted Answer · 2010-07-03 21:10:14Z

2

How about using some sort of Read/Write lock? The threads do their normal work (in relatively small chunks, so they can be interrupted in a timely fashion) as a reader, and the thread that needs to change IP does so as a writer.

answered Jul 3, 2010 at 21:10

pdbartlett

1,51910 silver badges18 bronze badges

2 Comments

Novice Over a year ago

Thankyou for your answer. I've edited my question. Please see it and advice me how can I implement read/write lock

pdbartlett Over a year ago

As @rmarimon suggests, an implementation of Java's own ReadWriteLock (such as ReentrantReadWriteLock: java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/locks/…) is the obvious answer and probably your best option. There are probably other libraries around with more specialist versions, though, should you find you need something else.

Ricardo Marimon · Accepted Answer · 2010-07-03 21:31:51Z

0

Try this class ReadWriteLock in the java 1.5 api.

answered Jul 3, 2010 at 21:31

Ricardo Marimon

10.8k9 gold badges55 silver badges62 bronze badges

Collectives™ on Stack Overflow

Java Pause Execution

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related