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/* *******************************************************************
 * Copyright (c) 2008 Contributors
 * All rights reserved. 
 * This program and the accompanying materials are made available 
 * under the terms of the Eclipse Public License v1.0 
 * which accompanies this distribution and is available at 
 * http://www.eclipse.org/legal/epl-v10.html 
 * Contributors: 
 *     Andy Clement     initial implementation 
 * ******************************************************************/
package org.aspectj.weaver;

import java.lang.ref.WeakReference;

 * Wraps a reference to a classloader inside a WeakReference. This should be used where we do not want the existence of a
 * classloader reference to prevent garbage collection of that classloader (and possibly an associated weaver instance in the case
 * of load time weaving).
 * <p>
 * In more detail:<br>
 * When load time weaving, the class Aj maintains a WeakHashMap from the classloader instance to a weaver instance. The aim is that
 * the weaver is around as long as the classloader is and should the classloader be dereferenced then the weaver can also be garbage
 * collected. The problem is that if there are many references to the classloader from within the weaver, these are considered hard
 * references and cause the classloader to be long lived - even if the user of the classloader has dereferenced it in their code.
 * The solution is that the weaver should use instances of WeakClassLoaderReference objects - so that when the users hard reference
 * to the classloader goes, nothing in the weaver will cause it to hang around. There is a big assertion here that the
 * WeakClassLoaderReference instances will not 'lose' their ClassLoader references until the top level ClassLoader reference is
 * null'd. This means there is no need to check for the null case on get() in this WeakReference logic below, because we shouldn't
 * be using this weaver if its associated ClassLoader has been collected. See https://bugs.eclipse.org/bugs/show_bug.cgi?id=210470
 * @author Andy Clement
00035 public class WeakClassLoaderReference {

      protected final int hashcode;

      private final WeakReference loaderRef;

      public WeakClassLoaderReference(ClassLoader loader) {
            loaderRef = new WeakReference(loader);
            hashcode = loader.hashCode() * 37;

      public ClassLoader getClassLoader() {
            ClassLoader instance = (ClassLoader) loaderRef.get();
            // Assert instance!=null
            return instance;

      public boolean equals(Object obj) {
            if (!(obj instanceof WeakClassLoaderReference))
                  return false;
            WeakClassLoaderReference other = (WeakClassLoaderReference) obj;
            return (other.hashcode == hashcode);

      public int hashCode() {
            return hashcode;


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