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Editorial Team
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Asked: 2026-05-24T23:53:11+00:00

I’ve started reading about the singleton session bean and the annotations used to employ

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I’ve started reading about the singleton session bean and the annotations used to employ container managed concurrency. I don’t see the benfit of this compared to simply using the ‘synchronized’ keyword, so I suspect there is something important I am missing. Consider this example from the book “Enterprise JavaBeans 3.1” by Rubinger & Burke, O’Reilly:

@javax.ejb.Lock(javax.ejb.LockType.READ)
public String concurrentReadOnlyMethod(){...}

@javax.ejb.Lock(javax.ejb.LockType.WRITE)
public void allowOnlyOneWriteAtATimeMethod(String stringToSet){...}

How is this better than omitting the annotation all toghether in the read-case and using the synchronized keyword in the write-case, like this:

public String concurrentReadOnlyMethod(){...}

public synchronized void allowOnlyOneWriteAtATimeMethod(String stringToSet){...}
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1 Answer

  1. Editorial Team

    Simple.

    The “concurrentReadOnlyMethod” is not synchronized at all, so it doesn’t gain other side effect of synchronization (such as effects on variables within the memory model). Also, the READ lock will block the WRITE lock, so with just synchronized, you can have two threads running both methods simultaneously, whereas with the READ/WRITE lock you won’t.

    Obviously there’s more value when you have several READ locks and few WRITE locks, as all of the READ locks can be shared and run simultaneously, while the WRITE locks act more like a normal synchronized.

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