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.

Field Summary

protected Environment

environment

Constructor Summary

LRUCache(Storage storage, int maximumSize, Environment env)
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 metadata, 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	flush(Continuation c) Method which is used to erase all data stored in the Cache.
long	getMaximumSize() Returns the maximum size of the cache, in bytes.
java.io.Serializable	getMetadata(Id id) Returns the metadata associated with the provided object, or null if no metadata exists.
void	getObject(Id id, Continuation c) Returns the object identified by the given id.
int	getSize() Returns the number of Ids currently stored in the catalog
Storage	getStorage() Returns the backing storage object
long	getTotalSize() Returns the total size of the stored data in bytes.
void	rename(Id oldId, Id newId, Continuation c) Renames the given object to the new id.
IdSet	scan() Return all objects currently stored by this catalog NOTE: This method blocks so if the behavior of this method changes and no longer stored in memory, this method may be deprecated.
IdSet	scan(IdRange range) Return the objects identified by the given range of ids.
java.util.SortedMap	scanMetadata() Returns a map which contains keys mapping ids to the associated metadata.
java.util.SortedMap	scanMetadata(IdRange range) Returns a map which contains keys mapping ids to the associated metadata.
java.util.SortedMap	scanMetadataValuesHead(java.lang.Object value) Returns the submapping of ids which have metadata less than the provided value.
java.util.SortedMap	scanMetadataValuesNull() Returns the submapping of ids which have metadata null
void	setMaximumSize(int size, Continuation c) Sets the maximum size of the cache, in bytes.
void	setMetadata(Id id, java.io.Serializable metadata, Continuation command) Updates the metadata stored under the given key to be the provided value.
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

Field Detail

environment

protected Environment environment

Constructor Detail

LRUCache

public LRUCache(Storage storage,
                int maximumSize,
                Environment env)

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

getStorage

public Storage getStorage()

Returns the backing storage object

Returns:

The storage backing this cache

rename

public void rename(Id oldId,
                   Id newId,
                   Continuation c)

Renames the given object to the new id. This method is potentially faster than store/cache and unstore/uncache.

Specified by:

rename in interface Catalog

Parameters:

oldId - The id of the object in question.

newId - The new id of the object in question.

c - The command to run once the operation is complete

cache

public void cache(Id id,
                  java.io.Serializable metadata,
                  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.

metadata - The object's metadata

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:

pid - The object's id

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.

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

getMetadata

public java.io.Serializable getMetadata(Id id)

Returns the metadata associated with the provided object, or null if no metadata exists. The metadata must be stored in memory, so this operation is guaranteed to be fast and non-blocking.

Specified by:

getMetadata in interface Catalog

Parameters:

id - The id for which the metadata is needed

Returns:

The metadata, or null of non exists

setMetadata

public void setMetadata(Id id,
                        java.io.Serializable metadata,
                        Continuation command)

Updates the metadata stored under the given key to be the provided value. As this may require a disk access, the requestor must also provide a continuation to return the result to.

Specified by:

setMetadata in interface Catalog

Parameters:

id - The id for the metadata

metadata - The metadata to store

c - The command to run once the operation is complete

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

scan

public IdSet scan()

Return all objects currently stored by this catalog NOTE: This method blocks so if the behavior of this method changes and no longer stored in memory, this method may be deprecated.

Specified by:

scan in interface Catalog

Returns:

The idset containg the keys

scanMetadata

public java.util.SortedMap scanMetadata(IdRange range)

Returns a map which contains keys mapping ids to the associated metadata.

Specified by:

scanMetadata in interface Catalog

Parameters:

range - The range to query

Returns:

The map containg the keys

scanMetadata

public java.util.SortedMap scanMetadata()

Returns a map which contains keys mapping ids to the associated metadata.

Specified by:

scanMetadata in interface Catalog

Returns:

The treemap mapping ids to metadata

scanMetadataValuesHead

public java.util.SortedMap scanMetadataValuesHead(java.lang.Object value)

Returns the submapping of ids which have metadata less than the provided value.

Specified by:

scanMetadataValuesHead in interface Catalog

Parameters:

value - The maximal metadata value

Returns:

The submapping

scanMetadataValuesNull

public java.util.SortedMap scanMetadataValuesNull()

Returns the submapping of ids which have metadata null

Specified by:

scanMetadataValuesNull in interface Catalog

Returns:

The submapping

getMaximumSize

public long getMaximumSize()

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

getSize

public int getSize()

Returns the number of Ids currently stored in the catalog

Specified by:

getSize in interface Catalog

Returns:

The number of ids in the catalog

getTotalSize

public long getTotalSize()

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

flush

public void flush(Continuation c)

Method which is used to erase all data stored in the Cache. Use this method with care!

Specified by:

flush in interface Catalog

Parameters:

c - The command to run once done