org.eclipse.persistence.internal.identitymaps.SoftCacheWeakIdentityMap Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of eclipselink Show documentation

EclipseLink build based upon Git transaction f2b9fc5

There is a newer version: 5.0.0-B03

/*
 * Copyright (c) 1998, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation from Oracle TopLink
package org.eclipse.persistence.internal.identitymaps;

import java.lang.ref.SoftReference;

import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.internal.sessions.AbstractSession;

/**
 * Purpose: A SoftCacheWeakIdentityMap is identical to the WeakIdentityMap, however the weak reference
 * can be a performance problem for some types of apps because it can cause too much garbage collection
 * of objects read causing them to be re-read and re-built (this defeats the purpose of the cache).
 * The SoftCacheWeakIdentityMap solves this through also holding a fixed number of objects in memory to improve caching.
 * 
Responsibilities:

 *  Guarantees identity
 * 
 Allows garbage collection
 * 
 Increases performance by maintaining a fixed size cache of MRU objects when memory is available.
 * 
 The default size of the reference cache is the max size.
 * 
 * @since TOPLink/Java 1.2
 */
public class SoftCacheWeakIdentityMap extends HardCacheWeakIdentityMap {

    public SoftCacheWeakIdentityMap(int size, ClassDescriptor descriptor, AbstractSession session, boolean isIsolated) {
        super(size, descriptor, session, isIsolated);
    }

    /**
     * Creates a Soft reference to the object.
     * @param object is the domain object to cache.
     */
    @Override
    public Object buildReference(Object object) {
        if (object != null) {
            return new SoftReference(object);
        } else {
            return null;
        }
    }

    /**
     * Checks if the object is null, or reference's object is null.
     * @param reference the object for hard or the reference for soft.
     */
    @Override
    public boolean hasReference(Object reference) {
        return (reference != null) && (((SoftReference)reference).get() != null);
    }
}