How to avoid two threads creating the same entity?

I seem to have a problem with a race-condition. Two threads are trying to
          create the same entity. One thread calls a finder with no success and
          creates the entity, meanwhile - before the entity gets persisted
          (ejbStore()) - the other thread also calls a finder with no success,
          creating the
          same entity.
          My transaction isolation level in the weblogic-ejb-jar.xml is
          <transaction-isolation>
          <isolation-level>TRANSACTION_READ_UNCOMMITTED</isolation-level>
          <method>
          <ejb-name>ejb</ejb-name>
          <method-name>*</method-name>
          </method>
          </transaction-isolation>
          I've also tried <isolation-level>TRANSACTION_SERIALIZABLE</isolation-level>
          with no significant change in behavior.
          In the ejb-jar.xml
          <container-transaction>
          <method>
          <ejb-name>ejb</ejb-name>
          <method-name>*</method-name>
          </method>
          <trans-attribute>Required</trans-attribute>
          </container-transaction>

          Try setting delay-updates-until-end-of-tx to false for your bean. Try experimenting
          with concurrency-strategy of Exclusive. Or re-write your code to not check for
          existence before creation; just create the bean and let the db return a duplicate
          key exception.
          simon.
          "Daniel" <[email protected]> wrote:
          >I seem to have a problem with a race-condition. Two threads are trying
          >to
          >create the same entity. One thread calls a finder with no success and
          >creates the entity, meanwhile - before the entity gets persisted
          >(ejbStore()) - the other thread also calls a finder with no success,
          >creating the
          >same entity.
          >
          >My transaction isolation level in the weblogic-ejb-jar.xml is
          ><transaction-isolation>
          ><isolation-level>TRANSACTION_READ_UNCOMMITTED</isolation-level>
          ><method>
          ><ejb-name>ejb</ejb-name>
          ><method-name>*</method-name>
          ></method>
          ></transaction-isolation>
          >
          >I've also tried <isolation-level>TRANSACTION_SERIALIZABLE</isolation-level>
          >with no significant change in behavior.
          >
          >In the ejb-jar.xml
          ><container-transaction>
          ><method>
          ><ejb-name>ejb</ejb-name>
          ><method-name>*</method-name>
          ></method>
          ><trans-attribute>Required</trans-attribute>
          ></container-transaction>
          >
          >

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I made up a quick example that shows this behaviour: playing with "Do not sleep" and "Call ProcessSystemEvents" options you can see how threads execute.
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Proud to use LW/CVI from 3.1 on.
My contributions to the Developer Zone Community
If I have helped you, why not giving me a kudos?
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