/*
 * Copyright 2004 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *  
 */
                                                                                          
package sun.jvm.hotspot.tools;

import sun.jvm.hotspot.tools.*;

import sun.jvm.hotspot.oops.*;
import sun.jvm.hotspot.runtime.VM;
import sun.jvm.hotspot.utilities.SystemDictionaryHelper;
import sun.jvm.hotspot.utilities.ObjectReader;
import sun.jvm.hotspot.utilities.MarkBits;

import java.util.HashMap;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

/*
 * Iterates over the queue of object pending finalization and prints a
 * summary of these objects in the form of a histogram.
 */
public class FinalizerInfo extends Tool {
    public static void main(String[] args) {
        FinalizerInfo finfo = new FinalizerInfo();
        finfo.start(args);
        finfo.stop();
    }

    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 OopField queueField[] = new OopField[1];
        ik.iterateFields(new DefaultOopVisitor() {
	    public void doOop(OopField field, boolean isVMField) {
	        String name = field.getID().getName();
		if (name.equals("queue")) {
		    queueField[0] = field;
		}
	    }
        }, false);
        Oop queue = queueField[0].getValue(ik);	

        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());
	    }
       }

   }
}
