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Loopback exception example

Lucas Smith
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Joined: Apr 20, 2009
Posts: 804
    
    1

Hi,

I have read in Ivan Krizsan's notes (great job!) - page 65 (Reentrant locking) about loopback exception.

Why the following code does not throw mentioned exception?:

Could you give me an example when such exception can occur?


SCJP6, SCWCD5, OCE:EJBD6.
BLOG: http://leakfromjavaheap.blogspot.com
E Armitage
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Joined: Mar 17, 2012
Posts: 873
    
    9
a calling b here is very bad because most likely the @Lock(LockType.WRITE) is ignored since transaction and (just by inference) also concurrency attributes are only applied in a client view mode.
i.e the attributes are only applied when the business method is being invoked from some injected or looked up reference of the bean.
Here post and a will not throw exceptions because the container will allow multiple threads to access the methods
and b called through a is really run in READ mode as well. (i.e b is not considered a business method when called through method a).

To get an exception, set the @AccessTimeout value to zero for method b, make method b do some longish task and call method b twice (one call after another) from a client view of the bean or two different clients of the bean. The second call should get the javax.ejb.ConcurrentAccessException.
 
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