Module org.eclipse.persistence.core

Package org.eclipse.persistence.internal.identitymaps

Class HardCacheWeakIdentityMap

java.lang.Object

org.eclipse.persistence.internal.identitymaps.AbstractIdentityMap

org.eclipse.persistence.internal.identitymaps.FullIdentityMap

org.eclipse.persistence.internal.identitymaps.WeakIdentityMap

org.eclipse.persistence.internal.identitymaps.HardCacheWeakIdentityMap

All Implemented Interfaces:

Serializable, Cloneable, IdentityMap

Direct Known Subclasses:

SoftCacheWeakIdentityMap

public class HardCacheWeakIdentityMap
extends WeakIdentityMap

Purpose: A HardCacheWeakIdentityMap is identical to the weak identity map, 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 hard weak cache solves this by also holding a fixed number of objects in memory to improve caching.
This class makes use 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 by maintaining a fixed size cache of LRU objects when memory is available
• The default size of the reference cache is half the max size

Since:

TOPLink/Java 1.2

See Also:

• Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
class	HardCacheWeakIdentityMap.ReferenceCacheKey	Inner class to define the specialized weak cache key.

Field Summary

Fields

Modifier and Type	Field	Description
protected ExposedNodeLinkedList	referenceCache	A subset of cache entries have hard references maintained in this list to reduce garbage collection frequency

Fields inherited from class org.eclipse.persistence.internal.identitymaps.WeakIdentityMap

cleanupCount, cleanupSize

Fields inherited from class org.eclipse.persistence.internal.identitymaps.FullIdentityMap

cacheKeys

Fields inherited from class org.eclipse.persistence.internal.identitymaps.AbstractIdentityMap

descriptor, isIsolated, maxSize, session

Constructor Summary

Constructors

Constructor	Description
HardCacheWeakIdentityMap(int size, ClassDescriptor descriptor, AbstractSession session, boolean isIsolated)

Method Summary

Modifier and Type	Method	Description
Object	buildReference(Object object)	Allows subclass to create a SoftReference to the object.
CacheKey	createCacheKey(Object primaryKey, Object object, Object writeLockValue, long readTime)	Use a ReferenceCacheKey that also stores the linked list node to manage the LRU sub-cache of references.
ExposedNodeLinkedList	getReferenceCache()	Return the linked reference cache.
boolean	hasReference(Object reference)	Checks if the object is null, or reference's object is null.
CacheKey	put(Object primaryKey, Object object, Object writeLockValue, long readTime)	Store the object in the cache at its primary key, and add to sub-cache list.
Object	remove(CacheKey cacheKey)	Remove the cache key from the map and the sub-cache list.
void	updateMaxSize(int maxSize)	This method will be used to update the max cache size.

Methods inherited from class org.eclipse.persistence.internal.identitymaps.WeakIdentityMap

checkCleanup, cleanupDeadCacheKeys, putCacheKeyIfAbsent

Methods inherited from class org.eclipse.persistence.internal.identitymaps.FullIdentityMap

clone, cloneKeys, collectLocks, elements, getCacheKey, getCacheKeys, getSize, getSize, keys, keys, lazyRelationshipLoaded, resetCacheKey, setCacheKeys

Methods inherited from class org.eclipse.persistence.internal.identitymaps.AbstractIdentityMap

acquireDeferredLock, acquireLock, acquireLockNoWait, acquireLockWithWait, acquireReadLockOnCacheKey, acquireReadLockOnCacheKeyNoWait, containsKey, get, getAllCacheKeysFromIdentityMapWithEntityPK, getAllFromIdentityMapWithEntityPK, getCacheKeyForLock, getCacheKeyWithReadLock, getDefaultIdentityMapClass, getDescriptor, getDescriptorClass, getMaxSize, getWrapper, getWriteLockValue, release, remove, setDescriptor, setMaxSize, setWrapper, setWriteLockValue, toString

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Details

referenceCache

protected ExposedNodeLinkedList referenceCache

A subset of cache entries have hard references maintained in this list to reduce garbage collection frequency

Constructor Details

HardCacheWeakIdentityMap

public HardCacheWeakIdentityMap(int size,
 ClassDescriptor descriptor,
 AbstractSession session,
 boolean isIsolated)

Method Details

createCacheKey

public CacheKey createCacheKey(Object primaryKey,
 Object object,
 Object writeLockValue,
 long readTime)

Use a ReferenceCacheKey that also stores the linked list node to manage the LRU sub-cache of references.

Overrides:

createCacheKey in class WeakIdentityMap

getReferenceCache

public ExposedNodeLinkedList getReferenceCache()

Return the linked reference cache.

buildReference

public Object buildReference(Object object)

Allows subclass to create a SoftReference to the object.

Parameters:

object - is the domain object to cache.

hasReference

public boolean hasReference(Object reference)

Checks if the object is null, or reference's object is null.

Parameters:

reference - the object for hard or the reference for soft.

remove

public Object remove(CacheKey cacheKey)

Remove the cache key from the map and the sub-cache list.

Specified by:

remove in interface IdentityMap

Overrides:

remove in class FullIdentityMap

Returns:

the object held within the CacheKey or null if no object cached for given cacheKey.

put

public CacheKey put(Object primaryKey,
 Object object,
 Object writeLockValue,
 long readTime)

Store the object in the cache at its primary key, and add to sub-cache list.

Specified by:

put in interface IdentityMap

Overrides:

put in class FullIdentityMap

Parameters:

primaryKey - is the primary key for the object.

object - is the domain object to cache.

writeLockValue - is the current write lock value of object, if null the version is ignored.

updateMaxSize

public void updateMaxSize(int maxSize)

This method will be used to update the max cache size.

Specified by:

updateMaxSize in interface IdentityMap

Overrides:

updateMaxSize in class AbstractIdentityMap