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Using Thread.notify()

Posted on 2008-10-31
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Last Modified: 2012-05-05
Hi,

I have a background thread which will sleep for 30 seconds at a time. I want to possibly wake it up prematurely from another thread. I thought I could do something like:

    Thread t1 = new Thread() {
        public void run() {
            while (m_run) {
                Thread.sleept(30000);
            }
        }
    }
    t1.start();

   // now main thread continues on, maybe wants to wake the thread up now:
   t1.interrupt();

Is that how you do it? What if the thread is already awake when interrupt() is called, or if it is already exiting sleep() just at the same moment the main thread is calling it? I see you can also do a wait()/notfiy() but then you need an additional object to act as the guard?

Thanks
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Question by:DJ_AM_Juicebox
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4 Comments
 

Author Comment

by:DJ_AM_Juicebox
ID: 22853447
To follow up, I may have multiple threads wanting to wake that one background thread up - so a request to wake up prematurely may come from a few different sources -
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Author Comment

by:DJ_AM_Juicebox
ID: 22853694
Hmm so using wait/notify works too, is this the correct usage?
if (m_thread == null) {
    m_waitGuard = new Object();
    
    m_thread = new Thread() {
        public void run() {
            while (m_run) {
                try { 
                    synchronized (m_waitGuard) {  
                        m_waitGuard.wait(30000);
                    }
                }
                catch (InterruptedException ex) {
                    Log.d("**", "I woke up!");
                }
            }
            Log.d("**", "Thread is exiting..");
        }
    };
    m_thread.start();
}
 
 
// Then on some event like a button press, I can prematurely wake the thread up:
public void onBtnPress()
{
    synchronized (m_waitGuard) {
        m_waitGuard.notifyAll();
    }
}

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CEHJ earned 2000 total points
ID: 22855000
I see you can also do a wait()/notfiy() but then you need an additional object to act as the guard?

That's the way to do it in Java without using the java.util.concurrency package and it can be seen here:

http://technojeeves.com/joomla/index.php/free/61-wait-and-notify-in-java

but you don't *have* to have a separate lock object - it can be done using the objects you already have.
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Expert Comment

by:CEHJ
ID: 22896643
:-)
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