org.apache.activemq.util
Class LFUCache<Key,Value>

java.lang.Object
  org.apache.activemq.util.LFUCache<Key,Value>

All Implemented Interfaces:

Map<Key,Value>

public class LFUCache<Key,Value>
extends Object
implements Map<Key,Value>

LFU cache implementation based on http://dhruvbird.com/lfu.pdf, with some notable differences:

• Frequency list is stored as an array with no next/prev pointers between nodes: looping over the array should be faster and more CPU-cache friendly than using an ad-hoc linked-pointers structure.
• The max frequency is capped at the cache size to avoid creating more and more frequency list entries, and all elements residing in the max frequency entry are re-positioned in the frequency entry linked set in order to put most recently accessed elements ahead of less recently ones, which will be collected sooner.
• The eviction factor determines how many elements (more specifically, the percentage of) will be evicted.

As a consequence, this cache runs in *amortized* O(1) time (considering the worst case of having the lowest frequency at 0 and having to evict all elements).

Author:

Sergio Bossa

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Constructor Summary

LFUCache(int maxCacheSize, float evictionFactor)

Method Summary

void	clear()
boolean	containsKey(Object o)
boolean	containsValue(Object o)
Set<Map.Entry<Key,Value>>	entrySet()
int	frequencyOf(Key k)
Value	get(Object k)
boolean	isEmpty()
Set<Key>	keySet()
Value	put(Key k, Value v)
void	putAll(Map<? extends Key,? extends Value> map)
Value	remove(Object k)
int	size()
Collection<Value>	values()

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Constructor Detail

LFUCache

public LFUCache(int maxCacheSize,
                float evictionFactor)

Method Detail

put

public Value put(Key k,
                 Value v)

Specified by:

put in interface Map<Key,Value>

putAll

public void putAll(Map<? extends Key,? extends Value> map)

Specified by:

putAll in interface Map<Key,Value>

get

public Value get(Object k)

Specified by:

get in interface Map<Key,Value>

remove

public Value remove(Object k)

Specified by:

remove in interface Map<Key,Value>

frequencyOf

public int frequencyOf(Key k)

clear

public void clear()

Specified by:

clear in interface Map<Key,Value>

keySet

public Set<Key> keySet()

Specified by:

keySet in interface Map<Key,Value>

values

public Collection<Value> values()

Specified by:

values in interface Map<Key,Value>

entrySet

public Set<Map.Entry<Key,Value>> entrySet()

Specified by:

entrySet in interface Map<Key,Value>

size

public int size()

Specified by:

size in interface Map<Key,Value>

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Map<Key,Value>

containsKey

public boolean containsKey(Object o)

Specified by:

containsKey in interface Map<Key,Value>

containsValue

public boolean containsValue(Object o)

Specified by:

containsValue in interface Map<Key,Value>