Re: [mdr-users] NullPointerException with IBM JRE

Thanks for the patch. I have to admit I do not understand (even after 
your explanation) how the IBM JRE works (when it makes the entries 
invalid and why your patch fixes that). Could you please point me to 
some web page containing the description of the problem?
Martin

Mike Martin wrote:

> (I tried filing a bug report on this but it seems my
> login doesn't have the necessary permission to do so.)
>
> Running under the IBM JRE produces a NullPointerException
> while trying to initialize a B-tree repository.
>
>     [java] [org.netbeans.mdr.Logger] Rebooting storage. Reason: 
> org.netbeans.mdr.persistence.StorageBadRequestException: Btree 
> repository mdr does not exist
>     [java] *********** Exception occurred ************ at Wed May 18 
> 15:11:12 CDT 2005
>     [java] org.netbeans.mdr.util.DebugException: Fatal error: 
> Repository boot/initialization failed with message: 
> java.lang.NullPointerException: null
>     [java]     at 
> org.netbeans.mdr.NBMDRepositoryImpl.initCheck(NBMDRepositoryImpl.java:753) 
>
>     [java]     at 
> org.netbeans.mdr.NBMDRepositoryImpl.getExtent(NBMDRepositoryImpl.java:298) 
>
>     [java]     at org.netbeans.lib.jmi.uml2mof.Main.init(Main.java:70)
>     [java]     at org.netbeans.lib.jmi.uml2mof.Main.main(Main.java:53)
>     [java] ANNOTATIONS:
>     [java] [null] Exception occurred:
>
> This is with latest sources as of today (May 18 2005)
> running on an IBM 1.4.1 JRE for z/OS:
>
>    $ java -version
>    java version "1.4.1"
>    Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1)
>    Classic VM (build 1.4.1, J2RE 1.4.1 IBM z/OS Persistent Reusable VM 
> build cm1411sr2a-20040515 (JIT enabled: jitc))
>
> That's right, I'm running MDR on a mainframe!
>
> I chased the problem and it's failing because some code
> in MDRCache is using Map.Entry objects after they've gone
> invalid.  The following patch fixes it:
>
>    Index: 
> mdr/src/org/netbeans/mdr/persistence/btreeimpl/btreestorage/MDRCache.java
>    ===================================================================
>    RCS file: 
> /cvs/mdr/src/org/netbeans/mdr/persistence/btreeimpl/btreestorage/MDRCache.java,v 
>
>    retrieving revision 1.16
>    diff -r1.16 MDRCache.java
>    455c455
>    <         result.addAll(newOnes.entrySet());
>    ---
>    >         result.addAll(new HashMap(newOnes).entrySet());
>    464c464
>    <         ArrayList result = new ArrayList(dirty.entrySet());
>    ---
>    >         ArrayList result = new ArrayList(new 
> HashMap(dirty).entrySet());
>
> This program demonstrates the difference between the Sun and IBM
> JREs re. Map views:
>
>    import java.util.*;
>
>    public class MapViews
>    {
>        public static void main(String[] args)
>        {
>            Map m = new HashMap();
>            m.put("key1", "value1");
>            m.put("key2", "value2");
>
>            Set s = new HashSet(m.entrySet());
>            m.clear();
>
>            System.out.println("Set s = " + s);
>        }
>    }
>
> With the Sun JRE this code outputs:
>
>    Set s = [key2=value2, key1=value1]
>
> while the IBM JRE outputs:
>
>    Set s = [null=null, null=null]
>
> Both are legal results.  The IBM version makes it clearer
> that Map.Entry objects are valid only for the duration of
> an iteration over the entrySet().
>
> Mike