fiftyone.mobile.detection.cache

Class Cache<K,V>

java.lang.Object

fiftyone.mobile.detection.cache.Cache<K,V>

Type Parameters:

K - Key for the cache items.

V - Value for the cache items.

Direct Known Subclasses:

Cache

public class Cache<K,V>
extends Object

Many of the entities used by the detector data set are requested repeatedly. The cache improves memory usage and reduces strain on the garbage collector by storing previously requested entities for a period of time to avoid the need to re-fetch them from the underlying storage mechanism.

The Least Recently Used (LRU) cache is used. LRU cache keeps track of what was used when in order to discard the least recently used items first. Every time a cache item is used the "age" of the item used is updated.

Cache is implemented using the doubly linked list of Nodes where each Node tracks the next and previous Node and contains a value. Cache entries are stored as a Key : Value pair.

For a vast majority of the real life environments a constant stream of unique User-Agents is a fairly rare event. Usually the same User-Agent can be encountered multiple times within a fairly short period of time as the user is making a subsequent request. Caching frequently occurring User-Agents improved detection speed considerably.

Some devices are also more popular than others and while the User-Agents for such devices may differ, the combination of components used would be very similar. Therefore internal caching is also used to take advantage of the more frequently occurring entities.

This class should not be called as it is part of the internal logic.

Constructor Summary

Constructors

Constructor and Description
Cache(int cacheSize) Constructs a new instance of the cache.
Cache(int cacheSize, ICacheLoader<K,V> loader) Constructs a new instance of the cache.

Method Summary

Modifier and Type	Method and Description
V	get(K key) Retrieves the value for key requested.
V	get(K key, ICacheLoader<K,V> loader) Retrieves the value for key requested.
long	getCacheMisses()
long	getCacheRequests()
double	getPercentageMisses()
void	resetCache() Resets the 'stats' for 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(int cacheSize)

Constructs a new instance of the cache.

Parameters:

cacheSize - The number of items to store in the cache.

Cache

public Cache(int cacheSize,
             ICacheLoader<K,V> loader)

Constructs a new instance of the cache.

Parameters:

cacheSize - The number of items to store in the cache.

loader - used to fetch items not in the cache.

Method Detail

getCacheMisses

public long getCacheMisses()

Returns:

number of cache misses.

getCacheRequests

public long getCacheRequests()

Returns:

number of requests received by the cache.

getPercentageMisses

public double getPercentageMisses()

Returns:

the percentage of times cache request did not return a result.

get

public V get(K key)
      throws IOException

Retrieves the value for key requested. If the key does not exist in the cache then the Fetch method of the cache's loader is used to retrieve the value.

Parameters:

key - or the item required.

Returns:

An instance of the value associated with the key.

Throws:

IOException - if there was a problem accessing data file.

get

public V get(K key,
             ICacheLoader<K,V> loader)
      throws IOException

Retrieves the value for key requested. If the key does not exist in the cache then the Fetch method is used to retrieve the value from another loader.

Parameters:

key - or the item required

loader - to fetch the items from

Returns:

An instance of the value associated with the key

Throws:

IOException - if there was a problem accessing data file.

resetCache

public void resetCache()

Resets the 'stats' for the cache.