MRUCache< KEY, VALUE > Class Template Reference

Class implementing a generic Most Recently Used cache. More...

#include <MRUCache.h>

Public Types
typedef std::pair< KEY, VALUE >	value_type
	type of elements stored in the cache
typedef boost::multi_index_container< value_type, boost::multi_index::indexed_by< boost::multi_index::sequenced<>, boost::multi_index::hashed_unique< boost::multi_index::member< value_type, KEY, &value_type::first > > > >	container_type
	type of container for the elements
typedef container_type::const_iterator	iterator
	iterator over all cached items, sorted by access: most recent used first
typedef container_type::template nth_index< 1 >::type::const_iterator	hash_iterator
	iterator over the hash index to the items

Public Member Functions
	MRUCache (size_t maxSize)
	Constructor setting the maximum number of cached items. More...
void	insert (const KEY &key, const VALUE &value)
	Insert a key value pair into the cache. More...
void	insert (const value_type &item)
	Insert a key value pair into the cache. More...
bool	retrieve (const KEY &key, VALUE &value)
	Retrieve a value from the cache if it exists. More...
iterator	begin () const
	Return iterator to the begin of the cache. More...
iterator	end () const
	Return iterator to the end of the cache.
size_t	size () const
	Return actual size of the cache.
void	clear ()
	Clear cache.
void	setMaxSize (size_t maxSize)
	Set maximum number of cache entries.
size_t	getMaxSize () const
	Get maximum number of cache entries.
unsigned int	getHits () const
	Get number of cache hits since creation/last clear.
unsigned int	getMisses () const
	Get number of cache misses since creation/last clear.
unsigned int	getOverflows () const
	Get number of overflows (dropped items) since creation/last clear.

Protected Member Functions
void	update (const iterator &item)
	Update an item, thus marking it as recently accessed and putting it to the front of the list. More...

Protected Attributes
container_type	m_container
	Container for the items.
size_t	m_maxSize
	Maximum size of the cache.
unsigned int	m_hits
	Number of hits.
unsigned int	m_misses
	Number of misses.
unsigned int	m_overflows
	Number of overflows.

Detailed Description

template<class KEY, class VALUE>
class Belle2::MRUCache< KEY, VALUE >

Class implementing a generic Most Recently Used cache.

It can be used to cache values which are needed repeatedly. The size is limited so only the N most recently accessed elements will be kept.

Usage: if you have elements of type VALUE which are uniquely identified by something of type KEY and you want to cache the last 100 of them because computation is expensive, than you can define a cache somewhere:

MRUCache<KEY, VALUE> cache(100);

and in your function you can do

VALUE calculate(const KEY &key){ VALUE value; if(!cache.retrieve(key,value)){ //calculate value here //and finally add to cache cache.insert(key,value); } return value; }

Template Parameters

KEY	Key type to identify entries of the cache
VALUE	Value type of the cache entries

Definition at line 48 of file MRUCache.h.

Constructor & Destructor Documentation

MRUCache()

MRUCache ( size_t  maxSize )

inlineexplicit

Constructor setting the maximum number of cached items.

Parameters

maxSize

Maximum number of cached Items

Definition at line 71 of file MRUCache.h.

: m_maxSize(maxSize), m_hits(0), m_misses(0), m_overflows(0) {}

Member Function Documentation

begin()

iterator begin ( ) const

inline

Return iterator to the begin of the cache.

Items are sorted by access: most recently inserted

Definition at line 118 of file MRUCache.h.

insert() [1/2]

void insert ( const KEY &  key, const VALUE &  value  )

inline

Insert a key value pair into the cache.

If the maximum size is reached, the least recently used item is dropped

Parameters

key	key to the new item
value	to the new item

Definition at line 79 of file MRUCache.h.

insert() [2/2]

void insert ( const value_type &  item )

inline

Insert a key value pair into the cache.

If the maximum size is reached, the least recently used item is dropped

Parameters

item	std::pair containing key and value of the new item

Definition at line 86 of file MRUCache.h.

retrieve()

bool retrieve ( const KEY &  key, VALUE &  value  )

inline

Retrieve a value from the cache if it exists.

Parameters

[in]	key	key for the value to retrieve
[out]	value	reference to the value. Will only be modified if an item is found

Returns

true if value could be found, false otherwise

Definition at line 104 of file MRUCache.h.

update()

void update ( const iterator &  item )

inlineprotected

Update an item, thus marking it as recently accessed and putting it to the front of the list.

Parameters

item	iterator to the item to update

Definition at line 150 of file MRUCache.h.

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The documentation for this class was generated from the following file:

• framework/core/include/MRUCache.h