Package org.eclipse.persistence.internal.identitymaps

Class CacheIdentityMap

java.lang.Object

org.eclipse.persistence.internal.identitymaps.AbstractIdentityMap

org.eclipse.persistence.internal.identitymaps.FullIdentityMap

org.eclipse.persistence.internal.identitymaps.CacheIdentityMap

All Implemented Interfaces:

Serializable, Cloneable, IdentityMap

public class CacheIdentityMap
extends FullIdentityMap

Purpose: A fixed size LRU cache

Using a linked list as well as the map from the superclass a LRU cache is maintained. When a get is executed the LRU list is updated and when a new object is inserted the object at the start of the list is deleted (provided the maxSize has been reached).

Responsibilities:

• Guarantees identity through primary key values
• Keeps the LRU linked list updated.

Since:

TOPLink/Java 1.0

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
protected LinkedCacheKey	first	Provide handles on the linked list
protected LinkedCacheKey	last	Provide handles on the linked list

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
CacheIdentityMap(int size, ClassDescriptor descriptor, AbstractSession session, boolean isolated)

Method Summary

Modifier and Type	Method	Description
CacheKey	createCacheKey(Object primaryKey, Object object, Object writeLockValue, long readTime)	Create the correct type of CacheKey for this map.
protected void	ensureFixedSize()	Reduces the size of the receiver down to the maxSize removing objects from the start of the linked list.
CacheKey	getCacheKey(Object primaryKeys, boolean forMerge)	Access the object within the table for the given primaryKey.
protected LinkedCacheKey	insertLink(LinkedCacheKey key)	Insert a new element into the linked list of LinkedCacheKeys.
protected CacheKey	putCacheKeyIfAbsent(CacheKey searchKey)	Also insert the link if the cacheKey is put.
Object	remove(CacheKey key)	Remove the LinkedCacheKey from the cache as well as from the linked list.
protected LinkedCacheKey	removeLink(LinkedCacheKey key)	Remove the LinkedCacheKey from the linked list.
void	updateMaxSize(int maxSize)	INTERNAL: This method will be used to update the max cache size, any objects exceeding the max cache size will be remove from the cache.

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

clone, cloneKeys, collectLocks, elements, getCacheKeys, getSize, getSize, keys, keys, lazyRelationshipLoaded, put, 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 Detail

first

protected LinkedCacheKey first

Provide handles on the linked list

last

protected LinkedCacheKey last

Provide handles on the linked list

Constructor Detail

CacheIdentityMap

public CacheIdentityMap(int size,
                        ClassDescriptor descriptor,
                        AbstractSession session,
                        boolean isolated)

Method Detail

createCacheKey

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

Description copied from class: AbstractIdentityMap

Create the correct type of CacheKey for this map.

Overrides:

createCacheKey in class AbstractIdentityMap

ensureFixedSize

protected void ensureFixedSize()

Reduces the size of the receiver down to the maxSize removing objects from the start of the linked list.

getCacheKey

public CacheKey getCacheKey(Object primaryKeys,
                            boolean forMerge)

Access the object within the table for the given primaryKey. Move the accessed key to the top of the order keys linked list to maintain LRU.

Specified by:

getCacheKey in interface IdentityMap

Overrides:

getCacheKey in class FullIdentityMap

Parameters:

primaryKeys - is the primary key for the object to search for.

Returns:

the LinkedCacheKey or null if none found for primaryKey

insertLink

protected LinkedCacheKey insertLink(LinkedCacheKey key)

Insert a new element into the linked list of LinkedCacheKeys. New elements (Recently Used) are added at the end (last). Callers of this method must synchronize on the start of the list (this.first).

Returns:

the added LinkedCacheKey

putCacheKeyIfAbsent

protected CacheKey putCacheKeyIfAbsent(CacheKey searchKey)

Also insert the link if the cacheKey is put.

Overrides:

putCacheKeyIfAbsent in class FullIdentityMap

remove

public Object remove(CacheKey key)

Remove the LinkedCacheKey from the cache as well as from the linked list.

Specified by:

remove in interface IdentityMap

Overrides:

remove in class FullIdentityMap

Returns:

the LinkedCacheKey to be removed.

removeLink

protected LinkedCacheKey removeLink(LinkedCacheKey key)

Remove the LinkedCacheKey from the linked list. Callers of this method must synchronize on the start of the list (this.first).

Returns:

the removed LinkedCacheKey.

updateMaxSize

public void updateMaxSize(int maxSize)

INTERNAL: This method will be used to update the max cache size, any objects exceeding the max cache size will be remove from the cache. Please note that this does not remove the object from the identityMap, except in the case of the CacheIdentityMap.

Specified by:

updateMaxSize in interface IdentityMap

Overrides:

updateMaxSize in class AbstractIdentityMap