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From tathagata roy <tatha....@gmail.com>
Subject Re: Apache Curator Shared Lock Revoking fails
Date Wed, 28 Oct 2015 21:46:27 GMT
Jordan,

I tried using InterProcessSemaphoreMutex but that too has problems which
are

If the 2nd thread creates a lock object on the basepath and without
acquiring it and tries to release it, the Exception
*java.lang.IllegalStateException:
Not acquired *is thrown. And the 2nd thread is not able to acquire the lock
in itself without releasing it.

Also if we go by the first approach you suggested of some kind of
intercommunication between threads, that would be a problem in real time as
instead of the threads being in the same JVM, the threads can be in
separate JVMs. So we cant notify threads running on a different JVM.

Do you think we can achieve this using the native zookeeper api?

Note: i am using version 2.8.0

Thanks for all your help and suggestions



On Wed, Oct 28, 2015 at 4:01 PM, tathagata roy <tatha.roy@gmail.com> wrote:

> Thanks I will try that out
>
> On Wed, Oct 28, 2015 at 4:00 PM, Jordan Zimmerman <
> jordan@jordanzimmerman.com> wrote:
>
>> Another thing is to use InterProcessSemaphoreMutex instead. It is a
>> non-reentrant lock and can be unlocked from any thread.
>>
>> -JZ
>>
>> On Oct 28, 2015, at 2:55 PM, tathagata roy <tatha.roy@gmail.com> wrote:
>>
>> Thanks Jordan for the response.
>>
>> I cannot use the strategy because the thread can hold multiple locks ,
>> and if i do that it will release all the locks. The example i have put in
>> the question is just a sample i was trying but in the actual project a
>> single thread holds multiple locks.
>>
>> Is there any other way i can do that?
>>
>> On Wed, Oct 28, 2015 at 3:43 PM, Jordan Zimmerman <
>> jordan@jordanzimmerman.com> wrote:
>>
>>> Your RevocationListener should interrupt the thread that holds the lock.
>>> Then, that thread can release the lock.
>>>
>>> -Jordan
>>>
>>> On Oct 28, 2015, at 2:19 PM, tathagata roy <tatha.roy@gmail.com> wrote:
>>>
>>> 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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