[Jython-users] Jython using Java Classes in OSGI container / bundle update problem

[timur m. <tim...@we...>]

Hello,

I am using Jython in an OSGI container (http://oscar.objectweb.org/ for 
example) and it works really well.

To me, OSGI containers provide two major advantages:
  1. dynamic linking on the level of Java packages
  2. dynamic updating of components (bundles) at runtime

I discovered a problem with 2. when using Jython. The problem 
manifests, when I update a bundle in which Jython is being used and a 
Jython script instantiates some of my Java classes (which might have 
been updated). When doing such an OSGI bundle update, my OSGI Java 
adapter class does infact (using the Jython interpreter) executes the 
new/updated version of my Jython script in the bundle. But for some 
reason, that Jython script then continues to used the old/previous 
version of my Java classes. Not the new/updated ones.

In order to fix this problem, I would need to gain a better 
understanding of how the Jython interpreter in normal cases discovers 
that Java classes in the classpath were modified. Since the VM is not 
restarted when an OSGI bundle get's updated, I might need to trigger 
this 'check for modified Java classes' manually, no?

Some additional info: in order to make Jython 'see' the dynamically 
provided Java packages in the first place, I do the following in my 
OSGI Java adapter class:

     sys = Py.getSystemState();
     sys.setClassLoader(new 
JythonClassLoader(getClass().getClassLoader()));

Making use of the following tiny class:

     /**
      * Custom classloader, used to make Jython respect it's parent 
classloader.
      *
      * This will make Java packages made available through a OSGI 
classloader
      * become accessable in Jython scripts.
      */

     public class JythonClassLoader extends ClassLoader
     {
       public JythonClassLoader(ClassLoader parent)
       {
         super(parent);
       }
     }

Then, I need to make any Java package, provided through the OSGI 
container, become available to the Jython script by using multiple:

     sys.add_package(packageName);

This is no problem, because all these package names can easily be 
retrieved. However, when the classes in these packages have been 
updated, they are not being used, but instead the old/non-updated 
version of these Java classes (the ones that were available the very 
first time Jython tried to instatiate them) are always used. Thus, the 
OSGI update does not result in a real update.

(I confirmed with the Oscar developers, that indeed the two versions 
(old and new) of the bundle are loaded in memory in parallel during the 
updated process. But Jython does for some reason not let go of the old 
version.)

Please help.

BR, Timur