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Re: EOEditingContexts with same Object store, different threads
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Re: EOEditingContexts with same Object store, different threads


  • Subject: Re: EOEditingContexts with same Object store, different threads
  • From: Jeff Schmitz <email@hidden>
  • Date: Sat, 04 Oct 2008 23:10:37 -0500

Yes, pool is an EO.  And yes, adding an unlock/lock sequence as shown below (is that the proper place?) seems to have fixed the problem (thanks!)

public class PoolSync {

  public synchronized boolean checkAndLock(Pool pool, String threadName, EOEditingContext ec) {
System.out.println("checkAndLock called by " + threadName + "for pool " + pool.name());
ec.unlock();
ec.lock();
if (!(pool.calculating())) {
   pool.calculating(true);
   ec.saveChanges();
   System.out.println("setCalculating true " + threadName + " for pool " + pool.name());
   return true;
} else {
System.out.println("checkAndLock returning false " + threadName + "for pool " + pool.name());

   return false;
}
  }

}


Now however, later in the processing I'm getting the exceptions shown below for two of the threads.  Can I assume this means I have some unbalanced lock/unlock pairs that I need to find?

Exception in thread "Thread 2" java.lang.IllegalMonitorStateException
at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:125)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1137)
at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:431)
at com.webobjects.eocontrol.EOEditingContext.unlock(EOEditingContext.java:4635)
at er.extensions.ERXEC.unlock(ERXEC.java:455)
at com.netbracketsfw.core.FileIO64.calcCanIWins64(FileIO64.java:1034)
at com.netbracketsfw.core.FileIO64$1.run(FileIO64.java:1465)
Exception in thread "Thread 1" java.lang.IllegalMonitorStateException
at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:125)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1137)
at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:431)
at com.webobjects.eocontrol.EOEditingContext.unlock(EOEditingContext.java:4635)
at er.extensions.ERXEC.unlock(ERXEC.java:455)
at com.netbracketsfw.core.FileIO64.calcCanIWins64(FileIO64.java:1034)
at com.netbracketsfw.core.FileIO64$1.run(FileIO64.java:1465)

On Oct 4, 2008, at 10:49 PM, Chuck Hill wrote:


On Oct 4, 2008, at 8:40 PM, Jeff Schmitz wrote:

Hello,
  I'm trying to run three threads that perform long calculations on data within the object space.  Each thread needs to check EO states set by the other threads at certain intervals to make sure that it isn't working on the same calculations as other threads.  When checking these states, each thread goes through a common sync point object of class PoolSync that has syncronized methods.


public class PoolSync {

  public synchronized boolean checkAndLock(Pool pool, String threadName, EOEditingContext ec) {
System.out.println("checkAndLock called by " + threadName + "for pool " + pool.name());
if (!(pool.calculating())) {
  pool.calculating(true);
  ec.saveChanges();
  System.out.println("setCalculating true " + threadName + " for pool " + pool.name());
  return true;
} else {
System.out.println("checkAndLock returning false " + threadName + "for pool " + pool.name());

  return false;
}
  }

}


I've set up each thread with its own editing context, with each having the same parent ObjectStoreCoordinator using the following code:


       EOObjectStoreCoordinator parentObjectStore = new EOObjectStoreCoordinator();
       EOEditingContext thread1EditingContext = ERXEC.newEditingContext(parentObjectStore);
       EOEditingContext thread2EditingContext = ERXEC.newEditingContext(parentObjectStore);
       EOEditingContext thread3EditingContext = ERXEC.newEditingContext(parentObjectStore);

This is the call thread1 makes:

poolSync.checkAndLockForCanIWins(pool, threadName, thread1EditingContext)

While the synchronized class seems to work as expected based on my IO output below, the editing contexts in each thread don't seem to be being kept up to date with states set from other threads.  I was under the impression that WO would do this for me automatically as soon as saveChanges was called as long as they shared the same parent ObjectStoreCoordinator.  Is that not the case?

Note that even though thread 1 sets pool.calculating to true for TESTPOOL, threads 2 and 3 later read the pool.calculating() state as False.


checkAndLock called by Thread 1for pool TESTPOOL
setCalculating true Thread 1 for pool TESTPOOL
checkAndLock called by Thread 3for pool TESTPOOL
setCalculating true Thread 3 for pool TESTPOOL
checkAndLock called by Thread 2for pool TESTPOOL
setCalculating true Thread 2 for pool TESTPOOL


Couple off the cuff guesses:

- is Pool an EO?  You need to unlock (and then relock) the EC to see changes saved in other editing contexts.  IIRC, locking then unlocking has the same effect without actually unlocking the EC.

- if Pool is not an EO, is calculating declared transient?

Chuck

--
Chuck Hill             Senior Consultant / VP Development

Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems.
http://www.global-village.net/products/practical_webobjects







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References: 
 >EOEditingContexts with same Object store, different threads (From: Jeff Schmitz <email@hidden>)
 >Re: EOEditingContexts with same Object store, different threads (From: Chuck Hill <email@hidden>)

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