org.apache.jcs.engine.memory

Class AbstractDoulbeLinkedListMemoryCache

java.lang.Object

org.apache.jcs.engine.memory.AbstractMemoryCache

org.apache.jcs.engine.memory.AbstractDoulbeLinkedListMemoryCache

All Implemented Interfaces:

java.io.Serializable, IMemoryCache, MemoryCache

Direct Known Subclasses:

FIFOMemoryCache, LRUMemoryCache, MRUMemoryCache

public abstract class AbstractDoulbeLinkedListMemoryCache
extends AbstractMemoryCache

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.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	AbstractDoulbeLinkedListMemoryCache.IteratorWrapper iteration aid
class	AbstractDoulbeLinkedListMemoryCache.MapEntryWrapper

Field Summary

Fields

Modifier and Type	Field and Description
protected int	hitCnt number of hits
protected DoubleLinkedList	list thread-safe double linked list for lru
protected int	missCnt number of misses

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

attr, cache, cacheName, cattr, chunkSize, map, status

Constructor Summary

Constructors

Constructor and Description
AbstractDoulbeLinkedListMemoryCache()

Method Summary

Methods

Modifier and Type	Method and Description
protected MemoryElementDescriptor	addFirst(ICacheElement ce) Adds a new node to the start of the link list.
protected MemoryElementDescriptor	addLast(ICacheElement ce) Adds a new node to the end of the link list.
protected abstract void	adjustListForGet(MemoryElementDescriptor me) Adjust the list as needed for a get.
protected abstract MemoryElementDescriptor	adjustListForUpdate(ICacheElement ce) Children implement this to control the cache expiration algorithm
java.util.Map	createMap() This is called by super initialize.
void	dumpCacheEntries() Dump the cache entries from first to list for debugging.
protected int	dumpCacheSize() Returns the size of the list.
void	dumpMap() Dump the cache map for debugging.
int	freeElements(int numberToFree) This instructs the memory cache to remove the numberToFree according to its eviction policy.
ICacheElement	get(java.io.Serializable key) Get an item from the cache If the item is found, it is removed from the list and added first.
java.util.Iterator	getIterator() Gets the iterator attribute of the LRUMemoryCache object
java.lang.Object[]	getKeyArray() 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 hub) For post reflection creation initialization.
boolean	remove(java.io.Serializable key) Removes an item from the cache.
void	removeAll() Remove all of the elements from both the Map and the linked list implementation.
protected ICacheElement	spoolLastElement() This spools the last element in the LRU, if one exists.
void	update(ICacheElement ce) Calls the abstract method updateList.
protected void	verifyCache() Checks to see if all the items that should be in the cache are.

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

dispose, getCacheAttributes, getCacheName, getCompositeCache, getGroupKeys, 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 list

thread-safe double linked list for lru

hitCnt

protected int hitCnt

number of hits

missCnt

protected int missCnt

number of misses

Constructor Detail

AbstractDoulbeLinkedListMemoryCache

public AbstractDoulbeLinkedListMemoryCache()

Method Detail

initialize

public void initialize(CompositeCache hub)

For post reflection creation initialization.

Specified by:

initialize in interface IMemoryCache

Overrides:

initialize in class AbstractMemoryCache

Parameters:

hub -

createMap

public java.util.Map createMap()

This is called by super initialize.

Specified by:

createMap in class AbstractMemoryCache

Returns:

new Hashtable()

update

public final void update(ICacheElement ce)
                  throws java.io.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

Specified by:

update in class AbstractMemoryCache

Parameters:

ce - The cache element, or entry wrapper

Throws:

java.io.IOException

adjustListForUpdate

protected abstract MemoryElementDescriptor adjustListForUpdate(ICacheElement ce)
                                                        throws java.io.IOException

Children implement this to control the cache expiration algorithm

Parameters:

ce -

Returns:

MemoryElementDescriptor the new node

Throws:

java.io.IOException

get

public final ICacheElement get(java.io.Serializable key)
                        throws java.io.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

Specified by:

get in class AbstractMemoryCache

Parameters:

key - Identifies item to find

Returns:

ICacheElement if found, else null

Throws:

java.io.IOException

adjustListForGet

protected abstract void adjustListForGet(MemoryElementDescriptor me)

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

Parameters:

me -

freeElements

public int freeElements(int numberToFree)
                 throws java.io.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:

java.io.IOException

spoolLastElement

protected ICacheElement spoolLastElement()
                                  throws java.lang.Error

This spools the last element in the LRU, if one exists.

Returns:

ICacheElement if there was a last element, else null.

Throws:

java.lang.Error

remove

public boolean remove(java.io.Serializable key)
               throws java.io.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

Specified by:

remove in class AbstractMemoryCache

Parameters:

key -

Returns:

true if the removal was successful

Throws:

java.io.IOException

removeAll

public void removeAll()
               throws java.io.IOException

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

Specified by:

removeAll in interface IMemoryCache

Overrides:

removeAll in class AbstractMemoryCache

Throws:

java.io.IOException

addFirst

protected MemoryElementDescriptor addFirst(ICacheElement 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 addLast(ICacheElement ce)

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

Parameters:

ce - The feature to be added to the First

Returns:

MemoryElementDescriptor

dumpMap

public void dumpMap()

Dump the cache map for debugging.

dumpCacheEntries

public void dumpCacheEntries()

Dump the cache entries from first to list for debugging.

dumpCacheSize

protected int dumpCacheSize()

Returns the size of the list.

Returns:

the number of items in the map.

verifyCache

protected void verifyCache()

Checks to see if all the items that should be in the cache are. Checks consistency between List and map.

getIterator

public java.util.Iterator getIterator()

Gets the iterator attribute of the LRUMemoryCache object

Specified by:

getIterator in interface IMemoryCache

Overrides:

getIterator in class AbstractMemoryCache

Returns:

The iterator value

getKeyArray

public java.lang.Object[] getKeyArray()

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

Specified by:

getKeyArray in interface IMemoryCache

Specified by:

getKeyArray in class AbstractMemoryCache

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

Overrides:

getStatistics in class AbstractMemoryCache

Returns:

statistics about the cache

See Also:

IMemoryCache.getStatistics()