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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 v 2.0
* which accompanies this distribution and is available at
* https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.txt
*
* 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).
*
* In more detail:
* 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, Abraham Nevado
*/
public class WeakClassLoaderReference{
protected final int hashcode;
private final WeakReference loaderRef;
public WeakClassLoaderReference(ClassLoader loader) {
loaderRef = new WeakReference(loader);
if(loader == null){
// Bug: 363962
// Check that ClassLoader is not null, for instance when loaded from BootStrapClassLoader
hashcode = System.identityHashCode(this);
}else{
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;
}
}