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From "Adrian Cumiskey (Commented) (JIRA)" <>
Subject [jira] [Commented] (OGNL-34) OgnlRuntime.getCompiler and thread-safety.
Date Sat, 29 Oct 2011 21:15:32 GMT


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.

> OgnlRuntime.getCompiler and thread-safety.
> ------------------------------------------
>                 Key: OGNL-34
>                 URL:
>             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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