jdbm.helper

Class LRUCache<K,V>

java.lang.Object

jdbm.helper.LRUCache<K,V>

public class LRUCache<K,V>
extends Object

This class implements a versioned lru cache. Entries in the cache are identified with a key. When clients get a reference to the an entry, they point to the same object. Hence when the client wants to update and put a new version of the entry to the cache, he should not modify the object it got through the get interface (might copy on write). As new versions of the entries are put, cache maintains the previous versions of the entry. CLients specify the version of the cache entry they want to read. Clients are supposed to update the minimum read version the clients might request so that cache can purge older versions of data. For now, this class assumes clients make sure that put operations are serialized.

Author:

Apache Directory Project

Constructor Summary

Constructors

Constructor and Description
LRUCache(EntryIO<K,V> entryIO, int cacheSize)

Method Summary

Modifier and Type	Method and Description
void	advanceMinReadVersion(long minVersion) Called as the minimum version that readers will use advances.
V	get(K key, long version, Serializer serializer, boolean neverReplace) Finds and returns the entry corresponding to the given key and version.
void	put(K key, V value, long newVersion, Serializer serializer, boolean neverReplace) Updates the entry identified with the key with the new value.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

LRUCache

public LRUCache(EntryIO<K,V> entryIO,
                int cacheSize)

Method Detail

advanceMinReadVersion

public void advanceMinReadVersion(long minVersion)

Called as the minimum version that readers will use advances. This lets cache get rid of the older versions of entries.

Parameters:

minVersion - mimimum version that will be read from the cache

put

public void put(K key,
                V value,
                long newVersion,
                Serializer serializer,
                boolean neverReplace)
         throws IOException,
                CacheEvictionException

Updates the entry identified with the key with the new value.

Parameters:

key - identifier of the entry

value - new value of the entry

newVersion - version of the new value

serializer - used in case of IO

neverReplace - true if caller wants to always keep the entry in cache

Throws:

IOException, - CacheEvictionException

IOException

CacheEvictionException

get

public V get(K key,
             long version,
             Serializer serializer,
             boolean neverReplace)
      throws IOException

Finds and returns the entry corresponding to the given key and version.

Parameters:

key - the identifier for the entry

version - version the caller want to read

serializer - used in case of IO

neverReplace - true if entry is never synced to disk( entry wont be read from disk if not found in memory )

Returns:

value read

Throws:

IOException

toString

public String toString()

Overrides:

toString in class Object