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https://issues.apache.org/jira/browse/VELOCITY-750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12795675#action_12795675
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Nathan Bubna commented on VELOCITY-750:
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The fundamental problem here is that anyone using a single RuntimeInstance in a
multi-threaded environment should generally be manually init-ing the runtime.
The lazy initialization was not really intended for such situations, and the
double-checked locking was meant more as a convenience than a guarantee.
With that said, i was under the impression this is NOT broken double checked
locking in Java 1.5+. See:
http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
(section about volatile at the bottom)
Unless i've misunderstood that (or it's wrong), the init() method is
synchronized and the initialized variable is marked volatile. The assignment
of the volatile initialized variable should not be reordered to happen before
the initialize[Foo]() calls. And the synchronized init() method shouldn't be
executing simultaneously in multiple threads on the same instance. But perhaps
i have mis-implemented the fixed pattern?
> org.apache.velocity.runtime.RuntimeInstance initialization is not ThreadSafe
> ----------------------------------------------------------------------------
>
> Key: VELOCITY-750
> URL: https://issues.apache.org/jira/browse/VELOCITY-750
> Project: Velocity
> Issue Type: Bug
> Components: Engine
> Affects Versions: 1.6.2, 1.6.x
> Environment: Vista, Java 1.6
> Reporter: Cenek Rauscher
> Fix For: 1.6.x
>
>
> Two threads call Velocity.evaluate() method.
> Call RuntimeInstance.parse() and requireInitialization() method.
> One thread trying make initialization, set "initializing" to true and the
> other thread does not wait until initialization is done and go on.
> At next line Parser parser = (Parser) parserPool.get() is
> NullPointerException thrown.
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