On 2013/2/25 2:58, 云达(Yunda) wrote:

    Hi all,

    When I used CLHSDB just now I met this error:
    hsdb> inspect 0x00000000ee255080
    instance of "java/io/InputStream" @ 0x00000000ee255080 @ 0x00000000ee255080 (size = 24)
    Exception in thread "main" java.lang.InternalError: unimplemented
             at sun.jvm.hotspot.oops.Oop.iterateFields(Oop.java:151)
             at sun.jvm.hotspot.oops.Instance.iterateFields(Instance.java:66)
             at sun.jvm.hotspot.oops.Oop.iterate(Oop.java:143)
             at sun.jvm.hotspot.ui.tree.OopTreeNodeAdapter.getChildCount(OopTreeNodeAdapter.java:65)
             at sun.jvm.hotspot.CommandProcessor$Command.printNode(CommandProcessor.java:231)
             at sun.jvm.hotspot.CommandProcessor$24.doit(CommandProcessor.java:1008)
             at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1897)
             at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1867)
             at sun.jvm.hotspot.CommandProcessor.run(CommandProcessor.java:1747)
             at sun.jvm.hotspot.CLHSDB.run(CLHSDB.java:91)
             at sun.jvm.hotspot.CLHSDB.main(CLHSDB.java:35)

    I found it’s caused by the code of sun.jvm.hotspot.oops.Oop.iterateFields():
       void iterateFields(OopVisitor visitor, boolean doVMFields) {
         if (doVMFields) {
           visitor.doCInt(mark, true);
           if (VM.getVM().isCompressedKlassPointersEnabled()) {
             throw new InternalError("unimplemented");
           } else {
             visitor.doMetadata(klass, true);
           }
         }
       }

    When compressed oops( which is by default) are used an InternalError of “unimplemented” will be throwed. But actually it can be implemented easily by just one line of code:

    visitor.doMetadata(compressedKlass, true);
    
    I checked the hotspot-rt repo and I found it was implemented this way before changeset 3601, the main implementation of NPG. Since 3601 changed a whole lot of stuff, the ‘compressedKlass’ field couldn’t get the right value, as in line 51:

    // compressedKlass = new CIntField(type.getCIntegerField("_metadata._compressed_klass"), 0);

    So the code in iterateFields() was changed to throwing an InternalError accordingly.

    But the ‘compressedKlass’ field can get the right value now. So I think it’s time to change the code back and here’s the diff against the latest hotspot-rt:

    diff -r 2f881161d085 agent/src/share/classes/sun/jvm/hotspot/oops/Oop.java
    --- a/agent/src/share/classes/sun/jvm/hotspot/oops/Oop.java Mon Feb 25 18:25:24 2013 +0800
    +++ b/agent/src/share/classes/sun/jvm/hotspot/oops/Oop.java Mon Feb 25 18:47:08 2013 +0800
    @@ -148,7 +148,7 @@
         if (doVMFields) {
           visitor.doCInt(mark, true);
           if (VM.getVM().isCompressedKlassPointersEnabled()) {
    - throw new InternalError("unimplemented");
    + visitor.doMetadata(compressedKlass, true);
           } else {
             visitor.doMetadata(klass, true);
           }

 Regards,
 Yunda