oracle.toplink.essentials.internal.identitymaps.HardCacheWeakIdentityMap Maven / Gradle / Ivy
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* of the Common Development and Distribution License
* (the "License"). You may not use this file except
* in compliance with the License.
*
* You can obtain a copy of the license at
* glassfish/bootstrap/legal/CDDLv1.0.txt or
* https://glassfish.dev.java.net/public/CDDLv1.0.html.
* See the License for the specific language governing
* permissions and limitations under the License.
*
* When distributing Covered Code, include this CDDL
* HEADER in each file and include the License file at
* glassfish/bootstrap/legal/CDDLv1.0.txt. If applicable,
* add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your
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*/
// Copyright (c) 1998, 2007, Oracle. All rights reserved.
package oracle.toplink.essentials.internal.identitymaps;
import java.util.*;
import oracle.toplink.essentials.internal.helper.linkedlist.*;
/**
* Purpose: A weak cache is identical to the weak identity map, however the weak
* 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 weak cache solves this through also holding a fixed number of objects is memory to improve caching.
* This makes used of an exposed node linked list to maintain the objects by storing the link nodes in the cache key.
*
Responsibilities:
* - Guarantees identity
*
- Allows garbage collection
*
- Increases performance through maintaining a fixed size cache of MRU objects when memory is available
*
- The default size of the reference cache is half the max size
*
* @since TOPLink/Java 1.2
*/
public class HardCacheWeakIdentityMap extends WeakIdentityMap {
protected ExposedNodeLinkedList referenceCache;
public HardCacheWeakIdentityMap(int size) {
super(size);
this.referenceCache = new ExposedNodeLinkedList();
}
/**
* Use a ReferenceCacheKey that also stores the linked list node to manage
* the LRU sub-cache of references.
*/
public CacheKey createCacheKey(Vector primaryKey, Object object, Object writeLockValue, long readTime) {
return new ReferenceCacheKey(primaryKey, object, writeLockValue, readTime);
}
/**
* Return the linked reference cache.
*/
public ExposedNodeLinkedList getReferenceCache() {
return referenceCache;
}
/**
* Creates a Soft reference if Required
* @param object is the domain object to cache.
*/
public Object buildReference(Object object) {
return object;
}
/**
* Checks if the object is null, or reference's object is null.
* @param the object for hard or the reference for soft.
*/
public boolean hasReference(Object reference) {
return reference != null;
}
/**
* Store the object in the cache with the cache key.
* Also store the linked list node in the cache key.
*/
protected void put(CacheKey cacheKey) {
ReferenceCacheKey referenceCacheKey = (ReferenceCacheKey)cacheKey;
LinkedNode node = getReferenceCache().addFirst(buildReference(referenceCacheKey.getObject()));
referenceCacheKey.setReferenceCacheNode(node);
super.put(cacheKey);
}
/**
* Remove the cache key from the map and the sub-cache list.
*/
public Object remove(CacheKey cacheKey) {
if (cacheKey == null) {
return null;
}
ReferenceCacheKey referenceCacheKey = (ReferenceCacheKey)cacheKey;
synchronized (this){
getReferenceCache().remove(referenceCacheKey.getReferenceCacheNode());
}
return super.remove(cacheKey);
}
/**
* This method will be used to update the max cache size.
*/
public synchronized void updateMaxSize(int maxSize) {
setMaxSize(maxSize);
// Remove the LRU items if max size exceeded.
while (getReferenceCache().size() > getMaxSize()) {
getReferenceCache().removeLast();
}
}
/**
* Inner class to define the specialized weak cache key.
* Keeps track of the linked list node to allow quick repositioning.
*/
public class ReferenceCacheKey extends WeakCacheKey {
protected LinkedNode referenceNode;
public ReferenceCacheKey(Vector primaryKey, Object object, Object writeLockValue, long readTime) {
super(primaryKey, object, writeLockValue, readTime);
}
public LinkedNode getReferenceCacheNode() {
return referenceNode;
}
public void setReferenceCacheNode(LinkedNode referenceNode) {
this.referenceNode = referenceNode;
}
public ExposedNodeLinkedList getReferenceCache() {
return referenceCache;
}
/**
* Notifies that cache key that it has been accessed.
* Allows the LRU sub-cache to be maintained,
* the cache node must be moved to the front of the list.
*/
public void updateAccess() {
// CR#3573797 must be synchronized on the map, not the cache key.
synchronized (HardCacheWeakIdentityMap.this) {
// Check if the node's contents is null (was removed),
// also the object is null on initial put of acquired cache key,
// or ref value may have garbage collected so reset it.
if (!hasReference(getReferenceCacheNode().getContents())) {
getReferenceCacheNode().setContents(buildReference(getObject()));
}
// This is a fast constant time operations because of the linked list usage.
getReferenceCache().moveFirst(getReferenceCacheNode());
// Remove the old LRU items if max size exceeded (if was removed).
while (getReferenceCache().size() > getMaxSize()) {
getReferenceCache().removeLast();
}
}
}
}
}