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From tathagata roy <tatha....@gmail.com>
Subject Re: Apache Curator Shared Lock Revoking fails
Date Wed, 28 Oct 2015 19:19:29 GMT
>
> All,
>
> I am trying to test the revocable Locking in Apache Curator. I have two
> threads which tries to acquire a lock. If the first test acquires the lock,
> the second thread can ask the first thread to release the lock so that the
> 2nd thread can acquire it
>
>           RetryPolicy retryPolicy = new ExponentialBackoffRetry(
> baseSleepTimeMills, maxRetries);
>
>         CuratorFramework client = CuratorFrameworkFactory.newClient(hosts, retryPolicy);
>         client.start();
>
>         final InterProcessMutex lock = new InterProcessMutex(client, lockBasePath);
>
>         Collection<String> nodes =  lock.getParticipantNodes();
>
>         lock.makeRevocable(new RevocationListener<InterProcessMutex>(){
>
>             @Override
>             public void revocationRequested(InterProcessMutex lock1) {
>                 try {
>                     if(lock.isAcquiredInThisProcess()){
>                         lock.release();
>                     }
>
>                 } catch (Exception e) {
>                     // TODO Auto-generated catch block
>                     e.printStackTrace();
>                 }
>
>             }
>
>         });
>
>         if(nodes!=null && !nodes.isEmpty()){
>             Revoker.attemptRevoke(client, nodes.iterator().next());
>         }
>
>         if (lock.acquire(waitTimeSeconds, TimeUnit.SECONDS)) {
>             try {
>                 doSomeWork(lockName);
>             } finally {
>                 lock.release();
>             }
>         } else {
>             System.err.printf("%s timed out after %d seconds waiting to acquire lock
on %s\n",
>                     lockName, waitTimeSeconds, lockPath);
>         }
>
>
> The problem is, when the 2nd thread calls the attemptRevoke, the callback
> async method is called on the first process, but since its a call back
> method that's a third thread, and if that invokes the lock.release it
> throws an Exception
>
> *java.lang.IllegalMonitorStateException: You do not own the lock*
>
> That is as per the api
>
> *release() Perform one release of the mutex if the calling thread is the
> same thread that acquired it.*
>
> So basically this is never possible because callbacks will always be
> another thread. Is my understanding right? Is there any other way to
> achieve this?
>
> Thanks for any suggestions
>
> -Tatha
>
>

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