[jboss-dev] Oops, javax.naming.spi.* is dependent on Hashtable, this will make it difficult to change the JBoss jndi naming service to use ConcurrentHashMap instead of Hashtable...

[Adrian]

On Wed, 2007-07-11 at 11:58 -0400, Scott Marlow wrote:
> Hi Adrian,
> 
> The 2-3 second contention that I'm seeing is on the following call stack:
> 
> "PooledInvokerThread-192.169.1.2: java.util.Hashtable.get :335
> PooledInvokerThread-192.169.1.2: org.jnp.interfaces.NamingContext.useAbsoluteName :1090
> PooledInvokerThread-192.169.1.2: org.jnp.interfaces.NamingContext.getObjectInstance :1123
> PooledInvokerThread-192.169.1.2: org.jnp.interfaces.NamingContext.getObjectInstanceWrapFailure :1142
> PooledInvokerThread-192.169.1.2: org.jnp.interfaces.NamingContext.lookup :705
> PooledInvokerThread-192.169.1.2: org.jnp.interfaces.NamingContext.lookup :587
> PooledInvokerThread-192.169.1.2: javax.naming.InitialContext.lookup :351
> PooledInvokerThread-192.169.1.2: org.hibernate.transaction.JTATransactionFactory.isTransactionInProgress :83
> PooledInvokerThread-192.169.1.2: org.hibernate.jdbc.JDBCContext.isTransactionInProgress :180
> PooledInvokerThread-192.169.1.2: org.hibernate.jdbc.JDBCContext.registerSynchronizationIfPossib :158
> PooledInvokerThread-192.169.1.2: org.hibernate.impl.SessionImpl.checkTransactionSynchStatus :1850
> PooledInvokerThread-192.169.1.2: org.hibernate.impl.SessionImpl.getEntityMode :1274
> PooledInvokerThread-192.169.1.2: org.hibernate.engine.StatefulPersistenceContext.addEntry :415
> PooledInvokerThread-192.169.1.2: org.hibernate.engine.StatefulPersistenceContext.addEntity :382
> PooledInvokerThread-192.169.1.2: org.hibernate.engine.TwoPhaseLoad.addUninitializedEntity :240
> PooledInvokerThread-192.169.1.2: org.hibernate.loader.Loader.loadFromResultSet :1358
> PooledInvokerThread-192.169.1.2: org.hibernate.loader.Loader.instanceNotYetLoaded :1300
> PooledInvokerThread-192.169.1.2: org.hibernate.loader.Loader.getRow :1197
> ..."
> 
> 
> I am looking at changing the Hashtable to a ConcurrentHashMap which 
> could help some applications run more concurrently. 

This just looks like a bug in Hibernate. 

It is caching the naming context in the JTATransactionFactory
and then using it concurrently across threads, without 
the required synchronization.

This probably only works by luck, because it is looking up in
"java:comp" for the UserTransaction which is a read only context
constructed at deployment time and is therefore unlikely 
to have concurrency problems.

I'm sure if this class was changed to create a new initial context
for each request you wouldn't see the contention, but that
might not be very efficient either. Depends how often the
isTransactionInProgress() is invoked.

I don't see why it isn't caching the UserTransaction instead anyway.
It's probably because some people use Hibernate across transaction
demarcation boundaries in at least dubious, if not broken ways. :-)
-- 
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Adrian Brock
Chief Scientist
JBoss, a division of Red Hat
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