org.apache.commons.jcs.engine.memory

Class AbstractDoubleLinkedListMemoryCache<K,V>

java.lang.Object

org.apache.commons.jcs.engine.memory.AbstractMemoryCache<K,V>

org.apache.commons.jcs.engine.memory.AbstractDoubleLinkedListMemoryCache<K,V>

All Implemented Interfaces:

IMemoryCache<K,V>

Direct Known Subclasses:

FIFOMemoryCache, LRUMemoryCache, MRUMemoryCache

public abstract class AbstractDoubleLinkedListMemoryCache<K,V>
extends AbstractMemoryCache<K,V>

This class contains methods that are common to memory caches using the double linked list, such as the LRU, MRU, FIFO, and LIFO caches.

Children can control the expiration algorithm by controlling the update and get. The last item in the list will be the one removed when the list fills. For instance LRU should more items to the front as they are used. FIFO should simply add new items to the front of the list.

Field Summary

Fields

Modifier and Type	Field and Description
protected DoubleLinkedList<MemoryElementDescriptor<K,V>>	list thread-safe double linked list for lru

Fields inherited from class org.apache.commons.jcs.engine.memory.AbstractMemoryCache

chunkSize, hitCnt, lock, map, missCnt, putCnt

Constructor Summary

Constructors

Constructor and Description
AbstractDoubleLinkedListMemoryCache()

Method Summary

Modifier and Type	Method and Description
protected MemoryElementDescriptor<K,V>	addFirst(ICacheElement<K,V> ce) Adds a new node to the start of the link list.
protected MemoryElementDescriptor<K,V>	addLast(ICacheElement<K,V> ce) Adds a new node to the end of the link list.
protected abstract void	adjustListForGet(MemoryElementDescriptor<K,V> me) Adjust the list as needed for a get.
protected abstract MemoryElementDescriptor<K,V>	adjustListForUpdate(ICacheElement<K,V> ce) Children implement this to control the cache expiration algorithm
ConcurrentMap<K,MemoryElementDescriptor<K,V>>	createMap() This is called by super initialize.
int	freeElements(int numberToFree) This instructs the memory cache to remove the numberToFree according to its eviction policy.
ICacheElement<K,V>	get(K key) Get an item from the cache If the item is found, it is removed from the list and added first.
Set<K>	getKeySet() Get an Array of the keys for all elements in the memory cache
IStats	getStatistics() This returns semi-structured information on the memory cache, such as the size, put count, hit count, and miss count.
void	initialize(CompositeCache<K,V> hub) For post reflection creation initialization.
boolean	remove(K key) Removes an item from the cache.
void	removeAll() Remove all of the elements from both the Map and the linked list implementation.
void	update(ICacheElement<K,V> ce) Calls the abstract method updateList.

Methods inherited from class org.apache.commons.jcs.engine.memory.AbstractMemoryCache

dispose, dumpMap, getCacheAttributes, getCacheName, getCompositeCache, getMultiple, getQuiet, getSize, getStatus, setCacheAttributes, waterfal

Methods inherited from class java.lang.Object

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

Field Detail

list

protected DoubleLinkedList<MemoryElementDescriptor<K,V>> list

thread-safe double linked list for lru

Constructor Detail

AbstractDoubleLinkedListMemoryCache

public AbstractDoubleLinkedListMemoryCache()

Method Detail

initialize

public void initialize(CompositeCache<K,V> hub)

For post reflection creation initialization.

Specified by:

initialize in interface IMemoryCache<K,V>

Overrides:

initialize in class AbstractMemoryCache<K,V>

Parameters:

hub -

createMap

public ConcurrentMap<K,MemoryElementDescriptor<K,V>> createMap()

This is called by super initialize. NOTE: should return a thread safe map

Specified by:

createMap in class AbstractMemoryCache<K,V>

Returns:

new ConcurrentHashMap()

update

public final void update(ICacheElement<K,V> ce)
                  throws IOException

Calls the abstract method updateList.

If the max size is reached, an element will be put to disk.

Specified by:

update in interface IMemoryCache<K,V>

Specified by:

update in class AbstractMemoryCache<K,V>

Parameters:

ce - The cache element, or entry wrapper

Throws:

IOException

adjustListForUpdate

protected abstract MemoryElementDescriptor<K,V> adjustListForUpdate(ICacheElement<K,V> ce)
                                                             throws IOException

Children implement this to control the cache expiration algorithm

Parameters:

ce -

Returns:

MemoryElementDescriptor the new node

Throws:

IOException

get

public final ICacheElement<K,V> get(K key)
                             throws IOException

Get an item from the cache If the item is found, it is removed from the list and added first.

Specified by:

get in interface IMemoryCache<K,V>

Specified by:

get in class AbstractMemoryCache<K,V>

Parameters:

key - Identifies item to find

Returns:

ICacheElement<K, V> if found, else null

Throws:

IOException

adjustListForGet

protected abstract void adjustListForGet(MemoryElementDescriptor<K,V> me)

Adjust the list as needed for a get. This allows children to control the algorithm

Parameters:

me -

freeElements

public int freeElements(int numberToFree)
                 throws IOException

This instructs the memory cache to remove the numberToFree according to its eviction policy. For example, the LRUMemoryCache will remove the numberToFree least recently used items. These will be spooled to disk if a disk auxiliary is available.

Parameters:

numberToFree -

Returns:

the number that were removed. if you ask to free 5, but there are only 3, you will get 3.

Throws:

IOException

remove

public boolean remove(K key)
               throws IOException

Removes an item from the cache. This method handles hierarchical removal. If the key is a String and ends with the CacheConstants.NAME_COMPONENT_DELIMITER, then all items with keys starting with the argument String will be removed.

Specified by:

remove in interface IMemoryCache<K,V>

Specified by:

remove in class AbstractMemoryCache<K,V>

Parameters:

key -

Returns:

true if the removal was successful

Throws:

IOException

removeAll

public void removeAll()
               throws IOException

Remove all of the elements from both the Map and the linked list implementation. Overrides base class.

Specified by:

removeAll in interface IMemoryCache<K,V>

Overrides:

removeAll in class AbstractMemoryCache<K,V>

Throws:

IOException

addFirst

protected MemoryElementDescriptor<K,V> addFirst(ICacheElement<K,V> ce)

Adds a new node to the start of the link list.

Parameters:

ce - The feature to be added to the First

Returns:

MemoryElementDescriptor

addLast

protected MemoryElementDescriptor<K,V> addLast(ICacheElement<K,V> ce)

Adds a new node to the end of the link list.

Parameters:

ce - The feature to be added to the First

Returns:

MemoryElementDescriptor

getKeySet

public Set<K> getKeySet()

Get an Array of the keys for all elements in the memory cache

Specified by:

getKeySet in interface IMemoryCache<K,V>

Specified by:

getKeySet in class AbstractMemoryCache<K,V>

Returns:

An Object[]

getStatistics

public IStats getStatistics()

This returns semi-structured information on the memory cache, such as the size, put count, hit count, and miss count.

Specified by:

getStatistics in interface IMemoryCache<K,V>

Overrides:

getStatistics in class AbstractMemoryCache<K,V>

Returns:

statistics about the cache

See Also:

IMemoryCache.getStatistics()