Hello,
I need to access an entity bean instance in a serial fashion, so I kindly 
request for any pattern to implement this.

The use case is similar to managing an account balance, the account must be 
blocked during modification. I need to block other requests until the resource 
is available (as if it was a printer).  That is why optimistic locking is not 
suitable.

I don't think synchronizing the SFSB which handles the entity bean is the best 
way since that would serialize invocation regardless of the entity bean 
instance been updated, I only  want to avoid concurrently modifying the same 
entity bean instance.

Jboss 4.0 official guide describes the transaction lock behaviour which: 
anonymous wrote : ensures that only one transaction at a time has access to a 
given entity bean

But it is not clear to me how this apply in the case, for example, of two 
entitymanagers loading same entity bean. Does it mean the second one's thread 
will be locked at that precise moment?

Also I don't quite grasp the behavior of entitymanager.lock(), what happens 
when another thread tries to lock one entity bean instance already locked? the 
locking effect is global to different entitymanager instances?

I deeply appreciate any advice

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