rice.persistence
Class LRUCache

java.lang.Object
  rice.persistence.LRUCache

All Implemented Interfaces:

Cache, Catalog

public class LRUCache

extends java.lang.Object

implements Cache

This class is an encapsulation of a least-recently-used (LRU) cache. It uses the provided storage service in order to store the cached data. If the Storage provides non-corruption services, these services will also be provided by this cache.

Constructor Summary

LRUCache(Storage storage, int maximumSize)
Builds a LRU cache given a storage object to store the cached data in and a maximum cache size.

Method Summary

void	cache(Id id, java.io.Serializable obj, Continuation c) Caches an object in this storage.
boolean	exists(Id id) Returns whether or not an object is cached in the location id.
void	exists(Id id, Continuation c) Returns whether or not an object is cached in the location id.
void	getMaximumSize(Continuation c) Returns the maximum size of the cache, in bytes.
void	getObject(Id id, Continuation c) Returns the object identified by the given id.
void	getTotalSize(Continuation c) Returns the total size of the stored data in bytes.
IdSet	scan(IdRange range) Return the objects identified by the given range of ids.
void	scan(IdRange range, Continuation c) Return the objects identified by the given range of ids.
void	setMaximumSize(int size, Continuation c) Sets the maximum size of the cache, in bytes.
void	uncache(Id id, Continuation c) Removes the object from the list of cached objects.

Methods inherited from class java.lang.Object

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

Constructor Detail

LRUCache

public LRUCache(Storage storage,
                int maximumSize)

Builds a LRU cache given a storage object to store the cached data in and a maximum cache size.

Parameters:

storage - The storage service to use as a back-end storage

maximumSize - The maximum size, in bytes, of storage to use

Method Detail

cache

public void cache(Id id,
                  java.io.Serializable obj,
                  Continuation c)

Caches an object in this storage. This method is non-blocking. If the object has already been stored at the location id, this method has the effect of calling uncachr(id) followed by cache(id, obj). This method finishes by calling receiveResult() on the provided continuation with whether or not the object was cached. Note that the object may not actually be cached due to the cache replacement policy. Returns True if the cache actaully stores the object, else False (through receiveResult on c).

Specified by:

cache in interface Cache

Parameters:

id - The object's id.

obj - The object to cache.

c - The command to run once the operation is complete

uncache

public void uncache(Id id,
                    Continuation c)

Removes the object from the list of cached objects. This method is non-blocking. If the object was not in the cached list in the first place, nothing happens and False is returned. Returns True if the action succeeds, else False (through receiveResult on c).

Specified by:

uncache in interface Cache

Parameters:

c - The command to run once the operation is complete

exists

public boolean exists(Id id)

Returns whether or not an object is cached in the location id.

Specified by:

exists in interface Catalog

Parameters:

id - The id of the object in question.

Returns:

Whether or not an object is present at id.

exists

public void exists(Id id,
                   Continuation c)

Returns whether or not an object is cached in the location id. The result is returned via the receiveResult method on the provided Continuation with an Boolean represnting the result.

Specified by:

exists in interface Catalog

Parameters:

c - The command to run once the operation is complete

id - The id of the object in question.

Returns:

Whether or not an object is present at id.

getObject

public void getObject(Id id,
                      Continuation c)

Returns the object identified by the given id.

Specified by:

getObject in interface Catalog

Parameters:

id - The id of the object in question.

c - The command to run once the operation is complete

Returns:

The object, or null if there is no cooresponding object (through receiveResult on c).

scan

public void scan(IdRange range,
                 Continuation c)

Return the objects identified by the given range of ids. The IdSet returned contains the Ids of the stored objects. The range is partially inclusive, the lower range is inclusive, and the upper exclusive. When the operation is complete, the receiveResult() method is called on the provided continuation with a IdSet result containing the resulting IDs.

Specified by:

scan in interface Catalog

Parameters:

c - The command to run once the operation is complete

Returns:

The idset containg the keys

scan

public IdSet scan(IdRange range)

Return the objects identified by the given range of ids. The IdSet returned contains the Ids of the stored objects. The range is partially inclusive, the lower range is inclusive, and the upper exclusive. NOTE: This method blocks so if the behavior of this method changes and uses the disk, this method may be deprecated.

Specified by:

scan in interface Catalog

Parameters:

range - The range to query

Returns:

The idset containg the keys

getMaximumSize

public void getMaximumSize(Continuation c)

Returns the maximum size of the cache, in bytes. The result is returned via the receiveResult method on the provided Continuation with an Integer representing the size.

Specified by:

getMaximumSize in interface Cache

Parameters:

c - The command to run once the operation is complete

getTotalSize

public void getTotalSize(Continuation c)

Returns the total size of the stored data in bytes. The result is returned via the receiveResult method on the provided Continuation with an Integer representing the size.

Specified by:

getTotalSize in interface Catalog

Parameters:

c - The command to run once the operation is complete

Returns:

The total size, in bytes, of data stored.

setMaximumSize

public void setMaximumSize(int size,
                           Continuation c)

Sets the maximum size of the cache, in bytes. Setting this value to a smaller value than the current value may result in object being evicted from the cache.

Specified by:

setMaximumSize in interface Cache

Parameters:

size - The new maximum size, in bytes, of the cache.

c - The command to run once the operation is complete

Returns:

The success or failure of the setSize operation (through receiveResult on c).