Java Code Examples for sun.jvm.hotspot.utilities.SystemDictionaryHelper#findInstanceKlass()

private static void SAInstanceKlassSize(int lingeredAppPid,
                                        String[] instanceKlassNames) {

    HotSpotAgent agent = new HotSpotAgent();
    try {
        agent.attach(lingeredAppPid);
    }
    catch (DebuggerException e) {
        System.out.println(e.getMessage());
        System.err.println("Unable to connect to process ID: " + lingeredAppPid);

        agent.detach();
        e.printStackTrace();
    }

    for (String instanceKlassName : instanceKlassNames) {
        InstanceKlass iKlass = SystemDictionaryHelper.findInstanceKlass(
                                   instanceKlassName);
        Asserts.assertNotNull(iKlass,
            String.format("Unable to find instance klass for %s", instanceKlassName));
        System.out.println("SA: The size of " + instanceKlassName +
                           " is " + iKlass.getSize());
    }
    agent.detach();
}
 

private static void SAInstanceKlassSize(int pid,
                                        String[] SAInstanceKlassNames) {
    HotSpotAgent agent = new HotSpotAgent();
    try {
        agent.attach(pid);
    }
    catch (DebuggerException e) {
        System.out.println(e.getMessage());
        System.err.println("Unable to connect to process ID: " + pid);

        agent.detach();
        e.printStackTrace();
    }

    for (String SAInstanceKlassName : SAInstanceKlassNames) {
        InstanceKlass ik = SystemDictionaryHelper.findInstanceKlass(
                           SAInstanceKlassName);
        Asserts.assertNotNull(ik,
            String.format("Unable to find instance klass for %s", ik));
        System.out.println("SA: The size of " + SAInstanceKlassName +
                           " is " + ik.getSize());
    }
    agent.detach();
}
 

private static void printBytecodes(String pid,
                                   String[] instanceKlassNames) {
    HotSpotAgent agent = new HotSpotAgent();
    try {
        agent.attach(Integer.parseInt(pid));
    }
    catch (DebuggerException e) {
        System.out.println(e.getMessage());
        System.err.println("Unable to connect to process ID: " + pid);

        agent.detach();
        e.printStackTrace();
    }

    for (String instanceKlassName : instanceKlassNames) {
        InstanceKlass iKlass = SystemDictionaryHelper.findInstanceKlass(instanceKlassName);
        MethodArray methods = iKlass.getMethods();
        for (int i = 0; i < methods.length(); i++) {
            Method m = methods.at(i);
            System.out.println("Method: " + m.getName().asString() +
                               " in instance klass: " + instanceKlassName);
            HTMLGenerator gen = new HTMLGenerator(false);
            System.out.println(gen.genHTML(m));
        }
    }
    agent.detach();
}
 

private static void printDefaultMethods(String pid,
                                        String[] instanceKlassNames) {
    HotSpotAgent agent = new HotSpotAgent();
    try {
        agent.attach(Integer.parseInt(pid));
    }
    catch (DebuggerException e) {
        System.out.println(e.getMessage());
        System.err.println("Unable to connect to process ID: " + pid);

        agent.detach();
        e.printStackTrace();
    }

    for (String instanceKlassName : instanceKlassNames) {
        InstanceKlass iKlass = SystemDictionaryHelper.findInstanceKlass(instanceKlassName);
        MethodArray methods = iKlass.getMethods();
        MethodArray defaultMethods = iKlass.getDefaultMethods();
        for (int i = 0; i < methods.length(); i++) {
            Method m = methods.at(i);
            System.out.println("Method: " + m.getName().asString() +
                               " in instance klass: " + instanceKlassName);
        }
        if (defaultMethods != null) {
            for (int j = 0; j < defaultMethods.length(); j++) {
                Method dm = defaultMethods.at(j);
                System.out.println("Default method: " + dm.getName().asString() +
                                   " in instance klass: " + instanceKlassName);
            }
        } else {
            System.out.println("No default methods in " + instanceKlassName);
        }

    }
    agent.detach();
}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}
 

public void run() {
     /*
      * The implementation here has a dependency on the implementation of
      * java.lang.ref.Finalizer. If the Finalizer implementation changes it's
      * possible this method will require changes too. We looked into using
      * ObjectReader to deserialize the objects from the target VM but as
      * there aren't any public methods to traverse the queue it means using
      * reflection which will also tie us to the implementation.
      *
      * The assumption here is that Finalizer.queue is the ReferenceQueue
      * with the objects awaiting finalization. The ReferenceQueue queueLength
      * is the number of objects in the queue, and 'head' is the head of the
      * queue.
      */
     InstanceKlass ik =
         SystemDictionaryHelper.findInstanceKlass("java.lang.ref.Finalizer");
     final Oop[] queueref = new Oop[1];
     ik.iterateStaticFields(new DefaultOopVisitor() {
         public void doOop(OopField field, boolean isVMField) {
           String name = field.getID().getName();
           if (name.equals("queue")) {
             queueref[0] = field.getValue(getObj());
           }
         }
       });
     Oop queue = queueref[0];

     InstanceKlass k = (InstanceKlass) queue.getKlass();

     LongField queueLengthField = (LongField) k.findField("queueLength", "J");
     long queueLength = queueLengthField.getValue(queue);

     OopField headField =  (OopField) k.findField("head", "Ljava/lang/ref/Reference;");
     Oop head = headField.getValue(queue);

     System.out.println("Number of objects pending for finalization: " + queueLength);

     /*
      * If 'head' is non-NULL then it is the head of a list of References.
      * We iterate over the list (end of list is when head.next == head)
      */
     if (head != null) {
         k = (InstanceKlass) head.getKlass();
         OopField referentField =
             (OopField) k.findField("referent", "Ljava/lang/Object;");
         OopField nextField =
             (OopField) k.findField("next", "Ljava/lang/ref/Reference;");

         HashMap map = new HashMap();
         for (;;) {
             Oop referent = referentField.getValue(head);

             Klass klass = referent.getKlass();
             if (!map.containsKey(klass)) {
                 map.put(klass, new ObjectHistogramElement(klass));
             }
             ((ObjectHistogramElement)map.get(klass)).updateWith(referent);

             Oop next = nextField.getValue(head);
             if (next == null || next.equals(head)) break;
             head = next;
         }

         /*
          * Sort results - decending order by total size
          */
         ArrayList list = new ArrayList();
         list.addAll(map.values());
         Collections.sort(list, new Comparator() {
           public int compare(Object o1, Object o2) {
               return ((ObjectHistogramElement)o1).compare((ObjectHistogramElement)o2);
           }
         });

         /*
          * Print summary of objects in queue
          */
         System.out.println("");
         System.out.println("Count" + "\t" + "Class description");
         System.out.println("-------------------------------------------------------");
         for (int i=0; i<list.size(); i++) {
             ObjectHistogramElement e = (ObjectHistogramElement)list.get(i);
             System.out.println(e.getCount() + "\t" + e.getDescription());
         }
    }

}