Created attachment 33760 [details]
Exception build 060909

For me it seems like a race condition in MergedClassPathImplementation.

BTW: The message "Change in unknown classpath" does seem to be very rational.
How the classpath can be unknown by its listener ;)

Tomasi, do you understand this assertion? I don't :)
Thanks

It seems as a racecondition caused by the fix of the
http://www.netbeans.org/issues/show_bug.cgi?id=75635.
1) The first thread removes the classpath from resourceMap in the sync block. 
this.resourceMap.remove (cp);
2) It leaves sync block
3) It calls addClasspathResource() outside sync block
4) Other thread enters sync block and tries to find the CP ---> assertion error
5) The first thread enters the sync block and adds CP into the resourceMap.

In my opinion replacing this.resourceMap.remove (cp); by this.resourceMap.get(cp);
should be OK, but I didn't tried tests yet.

I will try to run tests and let you know.

Created attachment 33770 [details]
Patch

The patch should like in this way. MCPImplTests are passing, but it requires
more testing.

Checking in
src/org/netbeans/modules/javacore/classpath/MergedClassPathImplementation.java;
/cvs/java/javacore/src/org/netbeans/modules/javacore/classpath/MergedClassPathImplementation.java,v
 <--  MergedClassPathImplementation.java
new revision: 1.29; previous revision: 1.28
done

Created attachment 33877 [details]
Patch

Reporter can you verify it in the release55_branch, otherwise I am not able to
integrate it into the NetBeans 5.5

Fabiola, can you verify the fix? Thanks

Is this issue integrated into NB 5.5 ? 
If not when do you want to do it ? 

Fabi, 
I think Tomas is waiting for your verification. 

No, it's not yet verified. It can be reproduced only in the ME designer.

The fix will be included in 6.0, because is not safe to integrate in MP 5.5 release

Reorganization of java component