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https://issues.apache.org/jira/browse/OGNL-34?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13139445#comment-13139445
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Adrian Cumiskey commented on OGNL-34:
-------------------------------------
I think making ExpressionCompiler a singleton is a good idea. If we did decide
to do this then we should also consider refactoring ExpressionCompiler as it
currently has many static methods - perhaps migrating all of them to a
companion ExpressionCompilerUtil.
I see two other options...
A) We take a small performance hit and wrap _compiler in a synchronized block.
B) We choose to not use the ClassResolver held by the OgnlContext but instead
use OgnlContext.DEFAULT_CLASS_RESOLVER for resolving. Then there wouldn't be
any need to synchronize access to _compiler because the resolution wouldn't be
dependent on OgnlContext, we could instantiate ExpressionCompiler immediately.
I think it would be a rare case that a custom class resolver would be required
to ensure that javaassist is available.
Thoughts?
> OgnlRuntime.getCompiler and thread-safety.
> ------------------------------------------
>
> Key: OGNL-34
> URL: https://issues.apache.org/jira/browse/OGNL-34
> Project: OGNL
> Issue Type: Bug
> Reporter: Maurizio Cucchiara
> Priority: Minor
> Labels: concurrency, thread-safety
>
> As you can see, {{getCompiler}} is not thread safe.
> I recently added a new performance benchmark to test its 3d-safety and
> performance: during my tests I have experienced a fast execution on unsafe
> version vs the safe one (though every concurrent test instantiated a new
> compiler).
> I have not yet investigated and I still don't know what can cause running
> more than one instance of the compiler in the same jvm. If necessary we can
> consider to make compiler a singleton in order to enforce this concept.
>
> What do you think guys?
> {code}
> public static OgnlExpressionCompiler getCompiler( OgnlContext ognlContext )
>
> {
>
> if ( _compiler == null )
>
> {
>
> try
>
> {
>
> OgnlRuntime.classForName( ognlContext, "javassist.ClassPool" );
>
> _compiler = new ExpressionCompiler();
>
> }
>
> catch ( ClassNotFoundException e )
>
> {
>
> throw new IllegalArgumentException(
>
> "Javassist library is missing in classpath! Please add missed
> dependency!", e );
> }
>
> }
>
> return _compiler;
>
> }
> {code}
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