[jboss-jira] [JBoss JIRA] Created: (JBRULES-2276) Thread-deadlock when Negation Was Used

Thu Sep 10 11:04:24 EDT 2009

Thread-deadlock when Negation Was Used
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                 Key: JBRULES-2276
                 URL: https://jira.jboss.org/jira/browse/JBRULES-2276
             Project: Drools
          Issue Type: Bug
      Security Level: Public (Everyone can see)
          Components: drools-core
    Affects Versions: 5.0.1.FINAL
         Environment: Drools version:  5.0.1
JDK version:       1.5.0_6
            Reporter: Freddy Andersen
            Assignee: Mark Proctor

A sever thread dead-lock was discovered when the Package instances were serialized/de-serialized, and then added to the RuleBase for execution.  In the attached unit test, the thread-lock would occur in a few seconds.  It seems the dead-lock would occur for conditions such as "rateTypeId not in (11,5)", and "rateTypeId != 11, rateTypeId != 5", while runs file with "rateTypeId in (11,5)" and "rateTypeId == 11 || rateTypeId == 5".

Please note that this test would not run without out fix in the previous submitted ticket JBRULES-2267.

Our Fix:
Removing the synchronized declaration in 2 places:
1.       CompositeClassLoader.loadClass at line 54.
2.       JavaDialectRuntimeData. PackageClassLoader.loadClass at line 451.

Rational: The thread-deadlock happens when one rule execution thread is competing with one package merging thread.  For class loading purpose, custom class loader objects are shared when the same Package objects are used in different RuleBuilders.  Although no instance attributes were changed for those class loader objects, a common cause to share the objects, they do share the thread locks.  When the object is locked, it's state changes, meaning it may not be a good idea to share those objects between threads.  On the other hand, there seems no need to synchronize those "loadClass" methods.  Thread lock is automatic when JVM's creates new classes.  The issue seems fixed after this simple change.

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