SUGGESTED FIX

/net/prt-archiver/data/archived_workspaces/main/gc_baseline/2006/20060806201917.jmasa.gc_baseline_6415354
                                     

SUGGESTED FIX

A second change was made for this bug to better detect
unparsable objects.

*** 6465,6479 ****
        // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
        // will dirty the card when the klass pointer is installed in the
        // object (signalling the completion of initialization).
      }
    } else {
!     // an unmarked object; ignore mark word in verification below
!     // since we are running concurrent with mutators
      assert(p->is_oop(true), "should be an oop"); 
      size = CompactibleFreeListSpace::adjustObjectSize(p->size());
    }
    assert(_markStack->isEmpty(), "post-condition (eager drainage)");
    assert(size > 0, "no unparsable object found");
    return size;
  }
  
--- 6466,6486 ----
        // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
        // will dirty the card when the klass pointer is installed in the
        // object (signalling the completion of initialization).
      }
    } else {
!     
!     // Either a not yet marked object or an uninitialized object:
!     // we merely need to compute its size so as to go look at the next
!     // block.
!     if (p->klass() == NULL || !p->is_parsable()) {
!       size = 0;   // An uninitialized object
!     } else {  // an object not (yet) reached by marking
        assert(p->is_oop(true), "should be an oop"); 
        size = CompactibleFreeListSpace::adjustObjectSize(p->size());
      }
+   }
    assert(_markStack->isEmpty(), "post-condition (eager drainage)");
    assert(size > 0, "no unparsable object found");
    return size;
  }
                                     

EVALUATION

During class file parsing there are slots that change from
an integer (constant pool index) to a reference.  These transitions
are done by the time the class has been created so are normally
not seen by other parts of the VM.  A class can be seen in transition
by CMS during precleaning if it is covered by a dirty card.
                                     

SUGGESTED FIX

The slots that changes from integer to references are tagged to
identify the current contents.  The slots only go from integer
to reference.  Currently the tag is changed from an integer tag
to a reference tag and then a reference is put into the slot.
Put a 0 in the slot before changing the tag.  A 0 will appear as
a NULL reference if the CMS precleaning finds the slot and will
be ignored.  When the reference is written into the slot, the
card covering the slot will be dirtied so the slot will be
revisited.