LruCache (51Degrees :: Device Detection

java.lang.Object
- fiftyone.mobile.detection.cache.LruCache<K,V>

Type Parameters:

K - Key for the cache items.

V - Value for the cache items.

All Implemented Interfaces:

ICache<K,V>, ILoadingCache<K,V>
```
public class LruCache<K,V>
extends Object
implements ILoadingCache<K,V>
```
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.
A variation of a 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.
This implementation supports concurrency by using multiple linked lists in place of a single linked list in the original implementation. The linked list to use is assigned at random and stored in the cached item. This will generate an even set of results across the different linked lists. The approach reduces the probability of the same linked list being locked when used in a environments with a high degree of concurrency. If the feature is not required then the constructor should be provided with a concurrency value of 1.
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.

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class LruCache.LruBuilder
- Nested classes/interfaces inherited from interface fiftyone.mobile.detection.cache.ICache
  ICache.Base<K,V>

Nested Classes
Modifier and Type	Class and Description
`static class`	`LruCache.LruBuilder`

Constructor Summary

Constructors
Constructor and Description
`LruCache(int cacheSize)` Constructs a new instance of the cache.
`LruCache(int cacheSize, int concurrency, IValueLoader<K,V> loader)` Constructs a new instance of the cache.
`LruCache(int cacheSize, IValueLoader<K,V> loader)` Constructs a new instance of the cache.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static ICacheBuilder`	`builder()` Return builder for an LRU cache
`V`	`get(K key)` Retrieves the value for key requested.
`V`	`get(K key, IValueLoader<K,V> loader)` Retrieves the value for key requested.
`long`	`getCacheMisses()` The number of requests that could not be served
`long`	`getCacheRequests()` The number of requests made to the cache
`long`	`getCacheSize()` The number of items the cache lists should have capacity for.
`double`	`getPercentageMisses()` a fraction < 1 (not a percentage) misses/requests
`void`	`resetCache()` Resets the 'stats' for the cache.
`void`	`setCacheLoader(IValueLoader<K,V> loader)` Loader used to fetch items not in the cache.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - LruCache
```
public LruCache(int cacheSize)
```
    Constructs a new instance of the cache.
    
    Parameters:
    
    cacheSize - The number of items to store in the cache.
  - LruCache
```
public LruCache(int cacheSize,
                IValueLoader<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.
  - LruCache
```
public LruCache(int cacheSize,
                int concurrency,
                IValueLoader<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
  - setCacheLoader
```
public void setCacheLoader(IValueLoader<K,V> loader)
```
    Loader used to fetch items not in the cache.
  - getCacheSize
```
public long getCacheSize()
```
    The number of items the cache lists should have capacity for.
    
    Specified by:
    
    getCacheSize in interface ICache<K,V>
    
    Returns:
    
    capacity of the cache.
  - getCacheMisses
```
public long getCacheMisses()
```
    Description copied from interface: ICache
    
    The number of requests that could not be served
    
    Specified by:
    
    getCacheMisses in interface ICache<K,V>
    
    Returns:
    
    number of cache misses.
  - getCacheRequests
```
public long getCacheRequests()
```
    Description copied from interface: ICache
    
    The number of requests made to the cache
    
    Specified by:
    
    getCacheRequests in interface ICache<K,V>
    
    Returns:
    
    number of requests received by the cache.
  - getPercentageMisses
```
public double getPercentageMisses()
```
    Description copied from interface: ICache
    
    a fraction < 1 (not a percentage) misses/requests
    
    Specified by:
    
    getPercentageMisses in interface ICache<K,V>
    
    Returns:
    
    the percentage of times cache request did not return a result.
  - get
```
public V get(K key)
```
    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.
    
    Specified by:
    
    get in interface ICache<K,V>
    
    Parameters:
    
    key - or the item required.
    
    Returns:
    
    An instance of the value associated with the key.
    
    Throws:
    
    IllegalStateException - if there was a problem accessing data file.
  - get
```
public V get(K key,
             IValueLoader<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.
    
    Specified by:
    
    get in interface ILoadingCache<K,V>
    
    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.
    
    Specified by:
    
    resetCache in interface ICache<K,V>
  - builder
```
public static ICacheBuilder builder()
```
    Return builder for an LRU cache

Class LruCache<K,V>

Nested Class Summary

Nested classes/interfaces inherited from interface fiftyone.mobile.detection.cache.ICache

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

LruCache

LruCache

LruCache

Method Detail

setCacheLoader

getCacheSize

getCacheMisses

getCacheRequests

getPercentageMisses

get

get

resetCache

builder