Re: [Springframework-developer] CachedIntrospectionResults classCache leak

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As Juergen pointed out, if you find a static member hasn't been garbage 
collected, it just means its ClassLoader cannot be garbage collected 
yet, the static member is not necessarly at fault there.  For an 
explanation of the current behavior, see below.

For the solution, you can use a ServletContextListener to call 
java.beans.Introspector.flushCaches() when the ServletContext is detroy 
(which causes the ClassLoader to be thrown away).

>                 if (results == null) {
>                         // can throw BeansException
>                         results = new CachedIntrospectionResults(clazz);
>                         boolean cacheSafe = isCacheSafe(clazz);
>                         if (logger.isDebugEnabled()) {
>                                 logger.debug("Class [" + 
> clazz.getName() + "] is " + (!cacheSafe ? "not " : "") + "cache-safe");
>                         }
> *                        classCache.put(clazz, new 
> WeakReference(results));
> *                }

Since Spring 1.0.2, the current code of this method is the following :

        if (results == null) {
            // can throw BeansException
            results = new CachedIntrospectionResults(clazz);
            boolean cacheSafe = isCacheSafe(clazz);
            if (logger.isDebugEnabled()) {
                logger.debug("Class [" + clazz.getName() + "] is " + 
(!cacheSafe ? "not " : "") + "cache-safe");
            }
            if (cacheSafe) {
                classCache.put(clazz, results);
            }
            else {
                classCache.put(clazz, new WeakReference(results));
            }
        }

What the isCacheSafe(Class) method does is check if the clazz's 
ClassLoader is the
same as CachedIntrospectionResults, or a parent of it.  Because what 
prevent garbage
collection of a ClassLoader A is if a class of a ClassLoader B that is 
not for garbage
collection has a reference on a class (or instance) of the ClassLoader 
A.  However, if
A is a parent of B (or B == A), then A cannot be collected anyway.  
Which is why if clazz
is considered "cacheSafe", no WeakReference is necessary, and in such 
case it improve
performance.  For example, if the class introspected is a JDK class, or 
a Spring class, its
ClassLoader can never be collected before the CachedIntrospectionResults 
class.

> I don't understand about memory leak, weark or soft referance but I've 
> see that CachedIntrospectionResults is referenced by  
> CachedIntrospectionResults.classCache and there are 2 instances 
> (org.springframework.context.support.ResourceBundleMessageSource and 
> org.springframework.web.servlet.DispatcherServlet)

I don't know what causes the ClassLoader to be retained, but you cannot 
easily know what is the cause, just knowning that singletons instances 
are still in the JVM only proves that the ClassLoader has not been 
garbage collected.  The problem is that something in a parent (or 
sibling) ClassLoader still has a reference on a Class of your webapp's 
ClassLoader.  The trick is to find what is.

Guillaume

Claudio D'Angelo wrote:

> I've deployed the minimal application (see the spring's sample). There 
> isn't Quarts, ibatis or hibernate. There is a controller with a 
> test.jsp only.
>
> I don't understand about memory leak, weark or soft referance but I've 
> see that CachedIntrospectionResults is referenced by  
> CachedIntrospectionResults.classCache and there are 2 instances 
> (org.springframework.context.support.ResourceBundleMessageSource and 
> org.springframework.web.servlet.DispatcherServlet)
>
>
> Where I can call the java.beans.Introspector.flushCaches()?
>
> Please help. After 20 redeploy Tomcat goes in OutOfMemory and ELS craches
>
> At 15.17 15/07/2004 +0200, you wrote:
>
>> If this happens with Spring 1.0.2, it is typically caused by *other* 
>> code that causes a leak. The ClassLoader is then still around, also 
>> showing Spring classes like CachedIntrospectionResults. This is not 
>> Spring's fault: Spring classes just keep hanging around as a side effect.
>>  
>> Try calling "java.beans.Introspector.flushCaches()" on application 
>> shutdown. This is a typical source of such leaks: The JavaBeans 
>> Introspector might still refer to application classes. This is not 
>> caused by Spring: It's rather other libraries that use the 
>> Introspector, for example Quartz.
>>  
>> Juergen
>>  
>>
>> ________________________________
>>
>> Von: spr...@li... im Auftrag 
>> von Rod Johnson
>> Gesendet: Do 15.07.2004 14:38
>> An: spr...@li...
>> Betreff: Re: [Springframework-developer] CachedIntrospectionResults 
>> classCache leak
>>
>>
>>
>> Claudio
>>
>> What version of Spring is your analysis against?
>>
>> R
>>
>> ----- Original Message -----
>> From: "Claudio D'Angelo" <cla...@ob...>
>> To: <spr...@li...>
>> Sent: Thursday, July 15, 2004 10:26 AM
>> Subject: [Springframework-developer] CachedIntrospectionResults 
>> classCache
>> leak
>>
>>
>> > Hi,
>> > I'm analyzing with OptimizeIt my web application:
>> > when I redeploy the application I note that instances of
>> > CachedIntrospectionResults still in memory and for any redeploy the
>> > instances raise.
>>
>>
>>
>>
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>
> Grazie e buon lavoro
> ------------------------------------------------------------------------
> *Claudio D'Angelo
> *Software Consultant
> *ObjectWay S.p.A.
> *Via G.A. Boltraffio 7
> 20159 Milano (MI)
> *http://www.objectway.it <http://www.objectway.it/>
>
> *
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