ClassLoader Deadlock fix was: Re: Relationship to JSR 291 [was: Re: Bryan's comments]

[Adrian]

On Thu, 2007-05-24 at 11:00 +0100, Glyn Normington wrote:
> A better approach would be for the Java 7 platform to provide first
> class support for JSR 291. This boils down to standardising the
> experimental class loader deadlock fix ([1])

Fixing the deadlock just moves the problem.

You'll still get ClassCircularityErrors when competing threads
try to load classes using locks other than the classloader
synchronization or they don't synchronize on the loadClass()
or they release the lock during the classloading request
to let others have a go (again to avoid the deadlock).

This is because of the way the dictionary class determines
whether a circular load is occuring.

Although I haven't tried it with OpenJDK so maybe the
dictionary class contains some other fixes to workaround the
problem?

The simple form of the problem:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4699981
has been fixed in recent JDKs, but spurious CCEs
still exist in other cases.
e.g. the testAbstractFactoryConcurrent() here:
http://viewvc.jboss.org/cgi-bin/viewvc.cgi/jbossas/projects/microcontainer/trunk/classloader/src/tests/org/jboss/test/classloader/delegate/test/DelegateUnitTestCase.java?revision=62792&view=markup
will show CCEs in the log if you enable TRACE logging.

1445 TRACE [ClassLoaderManager] Run failed with exception
java.lang.ClassCircularityError:
org/jboss/test/classloader/delegate/support/b/TestFactoryImplementation
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
--
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Adrian Brock
Chief Scientist
JBoss, a division of Red Hat
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