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  [SOLVED] Problem with threads and ReentrantLock  (Read 523 times)
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Offline Yemto

Junior Duke


Exp: 3 years



« Posted 2013-09-16 10:57:40 »

I have a problem with a reentrantLock, It never allows other threads to attain it.

The lock it self
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private static Lock update = new ReentrantLock();


There is the code I'm using.
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@Override
    public void run(){
        while(Village.running || !scheduled.isEmpty()){              
           
            //Tasks thats need to done
            CoreTask task = getNextTask();
            if(task != null){
                long taskStart = System.nanoTime();
                task.start(); tps++;
                taskTime += System.nanoTime()-taskStart;
            }
           
            //Update the whole game
            long now = System.nanoTime();
            if(update.tryLock()){
                update.lock();
                try{
                    hasLocked = true;
                    delta += (now - lastTime) / (1000000000.0 / Village.targetUPS);
                    lastTime = now;
                   
                    Village.screenUpdate();
                    while(1.0 <= delta){
                        Village.gameUpdate();
                        delta--;
                    }
                   
                    System.out.println("Thread "+getThread().getName()+" is going to sleep.");
                }finally{
                    update.unlock();
                    System.out.println("Thread "+getThread().getName()+" is napping. update is unlocked: "+update.tryLock());
                    try{Thread.sleep(10000);}catch(Exception e){}
                }
            }else{
                System.out.println("Thread "+getThread().getName()+" filed to get the lock");
            }

            if(now-time > 1000000000){
                time = now;
                updateAllCoreInfo();
            }
           
            Thread.yield();
        }//While method ends.
    }//Run method ends.



Here is the output
Quote
Thread Thread-2 is going to sleep.
Thread Thread-2 is napping. update is unlocked: true
Thread Thread-3 failed to get the lock
Thread Thread-3 failed to get the lock
Thread Thread-3 failed to get the lock
Thread Thread-3 failed to get the lock
Thread Thread-3 failed to get the lock

if I remove line 34 to 36 (the else statement) I get this
Quote
Thread Thread-2 is going to sleep.
Thread Thread-2 is napping. update is unlocked: true
Thread Thread-2 is going to sleep.
Thread Thread-2 is napping. update is unlocked: true
Thread Thread-2 is going to sleep.
Thread Thread-2 is napping. update is unlocked: true

Why don't Thread-3 get the lock even when Thread-2 is asleep?
Offline ClickerMonkey

JGO Coder


Medals: 20


Game Engineer


« Reply #1 - Posted 2013-09-16 12:10:44 »

You are doing this:

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if(update.tryLock()){
     update.lock();


That's double locking it. You need to unlock it twice then. Proper usage of tryLock is this:

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if (lock.tryLock()) {
  try {
    // do something
  } finally {
    lock.unlock();
  }
}


That should do it!

Offline Yemto

Junior Duke


Exp: 3 years



« Reply #2 - Posted 2013-09-16 13:12:24 »

Thank so much, I thought .tryLock() only tested if it was locked or not
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Offline ClickerMonkey

JGO Coder


Medals: 20


Game Engineer


« Reply #3 - Posted 2013-09-16 13:17:24 »

No problem! I'm glad you appreciate my help!

Offline Troncoso

JGO Coder


Medals: 20



« Reply #4 - Posted 2013-09-16 13:40:30 »

There you go. In case he didn't get the hint.
Offline Yemto

Junior Duke


Exp: 3 years



« Reply #5 - Posted 2013-09-16 14:40:56 »

oh sorry, I'm kind of new to this site so forgot about that. Sorry
Offline ClickerMonkey

JGO Coder


Medals: 20


Game Engineer


« Reply #6 - Posted 2013-09-16 15:20:15 »

Ha it's not required or anything.

I suspect it's secretly a competition and the winner gets a pony or something. So just in case it is, I like to *remind* people.

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