Package org.apache.lucene.util

Class DoubleBarrelLRUCache<K extends DoubleBarrelLRUCache.CloneableKey,V>

java.lang.Object

org.apache.lucene.util.DoubleBarrelLRUCache<K,V>

public final class DoubleBarrelLRUCache<K extends DoubleBarrelLRUCache.CloneableKey,V>
extends Object

Simple concurrent LRU cache, using a "double barrel" approach where two ConcurrentHashMaps record entries.

At any given time, one hash is primary and the other is secondary. get(K) first checks primary, and if that's a miss, checks secondary. If secondary has the entry, it's promoted to primary (NOTE: the key is cloned at this point). Once primary is full, the secondary is cleared and the two are swapped.

This is not as space efficient as other possible concurrent approaches (see LUCENE-2075): to achieve perfect LRU(N) it requires 2*N storage. But, this approach is relatively simple and seems in practice to not grow unbounded in size when under hideously high load.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	DoubleBarrelLRUCache.CloneableKey	Object providing clone(); the key class must subclass this.

Constructor Summary

Constructors

Constructor	Description
DoubleBarrelLRUCache(int maxSize)

Method Summary

Modifier and Type	Method	Description
V	get(K key)
void	put(K key, V value)

Methods inherited from class java.lang.Object

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

Constructor Detail

DoubleBarrelLRUCache

public DoubleBarrelLRUCache(int maxSize)

Method Detail

get

public V get(K key)

put

public void put(K key,
                V value)