IceUtil

Class Cache

java.lang.Object

IceUtil.Cache

public class Cache
extends java.lang.Object

An abstraction to efficiently maintain a cache, without holding a lock on the entire cache while objects are being loaded from their backing store. This class is useful mainly to implement evictors, such as used by Freeze.

See Also:

Store

Constructor Summary

Constructors

Constructor and Description
Cache(Store store) Initialize a cache using the specified backing store.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all entries from the cache.
java.lang.Object	getIfPinned(java.lang.Object key) Return the value stored for the given key from the cache.
java.lang.Object	pin(java.lang.Object key) Returns an object from the cache.
java.lang.Object	pin(java.lang.Object key, java.lang.Object o) Adds a key-value pair to the cache.
java.lang.Object	putIfAbsent(java.lang.Object key, java.lang.Object newObj) Adds a key-value pair to the cache.
int	size() Returns the number of entries in the cache.
java.lang.Object	unpin(java.lang.Object key) Removes the entry for the given key from the cache.

Methods inherited from class java.lang.Object

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

Constructor Detail

Cache

public Cache(Store store)

Initialize a cache using the specified backing store.

Parameters:

store - The backing store.

Method Detail

getIfPinned

public java.lang.Object getIfPinned(java.lang.Object key)

Return the value stored for the given key from the cache.

Parameters:

key - The key for the object to look up in the cache.

Returns:

If the cache contains an entry for the key, the return value is the object corresponding to the key; otherwise, the return value is null. getIfPinned does not call Store.load(java.lang.Object).

See Also:

Store.load(java.lang.Object)

unpin

public java.lang.Object unpin(java.lang.Object key)

Removes the entry for the given key from the cache.

Parameters:

key - The key for the entry to remove.

Returns:

If the cache contains an entry for the key, the return value is the corresponding object; otherwise, the return value is null.

clear

public void clear()

Removes all entries from the cache.

size

public int size()

Returns the number of entries in the cache.

Returns:

The number of entries.

pin

public java.lang.Object pin(java.lang.Object key,
                            java.lang.Object o)

Adds a key-value pair to the cache. This version of pin does not call Store.load(java.lang.Object) to retrieve an entry from backing store if an entry for the given key is not yet in the cache. This is useful to add a newly-created object to the cache.

Parameters:

key - The key for the entry.

o - The value for the entry.

Returns:

If the cache already contains an entry with the given key, the entry is unchanged and pin(Object, Object) returns the original value for the entry; otherwise, the entry is added and pin(Object, Object) returns null.

pin

public java.lang.Object pin(java.lang.Object key)

Returns an object from the cache. If no entry with the given key is in the cache, pin calls Store.load(java.lang.Object) to retrieve the corresponding value (if any) from the backing store.

Parameters:

key - The key for the entry to retrieve.

Returns:

Returns the value for the corresponding key if the cache contains an entry for the key. Otherwise, pin(Object) calls Store.load(java.lang.Object) and the return value is whatever is returned by load; if load throws an exception, that exception is thrown by pin(Object).

putIfAbsent

public java.lang.Object putIfAbsent(java.lang.Object key,
                                    java.lang.Object newObj)

Adds a key-value pair to the cache.

Parameters:

key - The key for the entry.

newObj - The value for the entry.

Returns:

If the cache already contains an entry for the given key, putIfAbsent returns the original value for that key. If no entry is for the given key is in the cache, putIfAbsent calls Store.load(java.lang.Object) to retrieve the corresponding entry (if any) from the backings store and returns the value returned by load. If the cache does not contain an entry for the given key and load does not return a value for the key, putIfAbsent adds the new entry and returns null.