Re: [Springframework-developer] CachedIntrospectionResults

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If the problem is related to the use of java.beans.Introspector that is =
caching BeanInfo's, then, as I said in a previous email, you need to =
have a javax.servlet.ServletContextListener, that has a call to =
java.beans.Instrospector.flushCaches() in the destroy method.  Spring =
1.1 will offer a built-in listener for such purpose =
(org.springframework.web.util.IntrospectorCleanupListener), but for =
previous version of Spring, you can create your own, it's a fairly =
simple class anyway.  You can see Spring's implementation at: =
http://cvs.sourceforge.net/viewcvs.py/springframework/spring/src/org/spri=
ngframework/web/util/IntrospectorCleanupListener.java?rev=3D1.1&view=3Dma=
rkup.  I would suggest to read that class' javadoc too.  Also, as it was =
mentionned by other people in answer to your mails, note that this =
problem is not Spring related, even if Spring do offers a workaround.

However, if such listener doesn't solve your problem, then I cannot help =
you without being able to reproduce the problem.  I can only tell you =
that if the Introspector is not the cause of the leak, you would need to =
track down what is the cause in order to solve you problem.

Guillaume

  ----- Original Message -----=20
  From: Claudio D'Angelo=20
  To: spr...@li...=20
  Sent: Monday, July 19, 2004 9:38 AM
  Subject: Re: [Springframework-developer] CachedIntrospectionResults

  I understend.
  But how can I save the application server from OutOfMemory or memory =
leak?
  My first problem is that after 20 redeploy the sever must be =
restarted.

  At 11.50 16/07/2004 -0400, you wrote:

    Claudio,

    I'm not completely sure to understand correctly your question, but I =
will try to answer as best as I can.

    WeakHashMap is implemented with WeakReference for keys, and strong =
reference for values.  That means if the value has a strong reference on =
the key, then the key cannot be garbage collected until the WeakHashMap =
is ready for collection.  However, if the value has no strong reference =
on its key, then being in the WeakHashMap won't prevent the key and =
value from being garbage collected if it is otherwise ready.  The =
WeakHashMap knows when to remove the key (and the value with it) by =
using the notification provided by the java.lang.ref package.  For more =
information on this, see: =
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/ref/package-summary.htm=
l

    So the problem here with the CachedIntrospectionResults is that it =
uses BeanInfo and PropertyDescriptor that both have strong reference to =
the class (indirectly by a reference on Methods of the class).  That =
will be solved with JDK 1.5 that uses a combinaison of Weak and Soft =
Reference to the Class and Method objects, but for 1.4.2, there's not =
really any better solution than to flush the Introspector's cache and/or =
use WeakReference on CachedIntrospectionResults. Using WeakReference on =
the CachedIntrospectionResults is safer, but decrease performance, and =
in such case a manual Instrospector.flushFromCaches(Class) must be used, =
so that the Instrospector does not keep a strong reference on the =
BeanInfo.

    When a webapp is hot-redeployed, a new ClassLoader is created to =
load the webapp, and the old one is thrown away, expected to be garbage =
collected.  For the collection to happen, the server must clear any =
strong reference to the ClassLoader or its classes, and also the webapp =
must make sure that any code in parent ClassLoaders (or siblings) clear =
any reference it might have to any of the webapp's class.

    Hopefully this answers your question, but if it does not (or if it's =
not clear enough), please give me more details of what information you =
need.

    Regards,
    Guillaume

    Claudio D'Angelo wrote:=20

      Thank's Guillaume.
      I'm studing about the WeakHashMap and I've seen that WeakHashMap =
build a weak reference on the key (it's right??), when the key hasn't =
any reference the entity is removed by map.

      Spring use a class type to save the key. When the class object =
haven't any reference? When the Classloader is shutdown?

      Can you explain to me (or advise to me if exists an article or =
tutorial) about?

      Thanks,
       Claudio

      At 10.05 15/07/2004 -0400, you wrote:

        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 =3D=3D null) {
                                  // can throw BeansException
                                  results =3D new =
CachedIntrospectionResults(clazz);
                                  boolean cacheSafe =3D =
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 =3D=3D null) {
                    // can throw BeansException
                    results =3D new CachedIntrospectionResults(clazz);
                    boolean cacheSafe =3D 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=20
        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=20
        collection has a reference on a class (or instance) of the =
ClassLoader A.  However, if=20
        A is a parent of B (or B =3D=3D 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:=20

          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.
            =20
            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.
            =20
            Juergen
            =20

            ________________________________

            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

          --=20
          La presente comunicazione potrebbe contenere informazioni =
riservate e/o protette=20
          da segreto professionale ed e' indirizzata esclusivamente ai =
destinatari della=20
          medesima qui indicati. Se avete ricevuto per errore la =
presente comunicazione,=20
          siete invitati a segnalarcelo, rispondendo a questo stesso =
indirizzo di e-mail,=20
          e a cancellare il presente messaggio dal Vostro sistema. E' =
strettamente proibito=20
          e potrebbe essere fonte di violazione di legge qualsiasi uso, =
comunicazione, copia=20
          o diffusione dei contenuti di questa comunicazione da parte di =
chi la abbia=20
          ricevuta per errore o in violazione degli scopi della =
presente.=20
          Il messaggio e' stato analizzato alla ricerca di virus o =
contenuti pericolosi ed=20
          e' risultato NON infetto.=20

      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

      --=20
      La presente comunicazione potrebbe contenere informazioni =
riservate e/o protette=20
      da segreto professionale ed e' indirizzata esclusivamente ai =
destinatari della=20
      medesima qui indicati. Se avete ricevuto per errore la presente =
comunicazione,=20
      siete invitati a segnalarcelo, rispondendo a questo stesso =
indirizzo di e-mail,=20
      e a cancellare il presente messaggio dal Vostro sistema. E' =
strettamente proibito=20
      e potrebbe essere fonte di violazione di legge qualsiasi uso, =
comunicazione, copia=20
      o diffusione dei contenuti di questa comunicazione da parte di chi =
la abbia=20
      ricevuta per errore o in violazione degli scopi della presente.=20
      Il messaggio e' stato analizzato alla ricerca di virus o contenuti =
pericolosi ed=20
      e' risultato NON infetto.=20
  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

  --=20
  La presente comunicazione potrebbe contenere informazioni riservate =
e/o protette=20
  da segreto professionale ed e' indirizzata esclusivamente ai =
destinatari della=20
  medesima qui indicati. Se avete ricevuto per errore la presente =
comunicazione,=20
  siete invitati a segnalarcelo, rispondendo a questo stesso indirizzo =
di e-mail,=20
  e a cancellare il presente messaggio dal Vostro sistema. E' =
strettamente proibito=20
  e potrebbe essere fonte di violazione di legge qualsiasi uso, =
comunicazione, copia=20
  o diffusione dei contenuti di questa comunicazione da parte di chi la =
abbia=20
  ricevuta per errore o in violazione degli scopi della presente.=20
  Il messaggio e' stato analizzato alla ricerca di virus o contenuti =
pericolosi ed=20
  e' risultato NON infetto. 