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Java example source code file (FinalizerInfo.java)

This example Java source code file (FinalizerInfo.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, comparator, defaultoopvisitor, finalizerinfo, hashmap, instanceklass, ljava\/lang\/object, ljava\/lang\/ref\/reference, longfield, objecthistogramelement, oop, oopfield, string, tool, util

The FinalizerInfo.java Java example source code

/*
 * Copyright (c) 2004, 2013, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

package sun.jvm.hotspot.tools;

import sun.jvm.hotspot.debugger.JVMDebugger;
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 FinalizerInfo() {
        super();
    }

    public FinalizerInfo(JVMDebugger d) {
        super(d);
    }

    public static void main(String[] args) {
        FinalizerInfo finfo = new FinalizerInfo();
        finfo.execute(args);
    }

    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());
            }
       }

   }
}

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