meta::caching::dblru_cache< Key, Value, Map > Class Template Reference

A double-barrel approach at a LRU cache. More...

#include <dblru_cache.h>

Public Member Functions
	dblru_cache (uint64_t max_size)
	Constructs a dlbru_cache with a given fixed size. More...
	dblru_cache (dblru_cache &&)
	dblru_cache may be move constructed.
dblru_cache &	operator= (dblru_cache)
	dlbru_cache may be be assigned. More...
	~dblru_cache ()=default
	Default destructor.
void	swap (dblru_cache &other)
	Swaps the current dlbru_cache with a given one. More...
void	insert (const Key &key, const Value &value)
	Insert a given (key, value) pair into the cache. More...
template<class... Args>
void	emplace (Args &&...args)
	Inserts a key value pair into the cache using in-place construction if possible. More...
util::optional< Value >	find (const Key &key)
	Finds a value in the cache. More...
void	clear ()
	Empties the cache. More...

Private Member Functions
void	handle_insert ()
	Helper function to ensure that the primary and secondary map swapping occurs at the correct moment.
std::shared_ptr< Map< Key, Value > >	get_primary_map () const
	Gets the primary map.
std::shared_ptr< Map< Key, Value > >	get_secondary_map () const
	Gets the secondary map.

Private Attributes
uint64_t	max_size_
	The maximum allowed size for the cache.
uint64_t	current_size_
	The current size of the primary map.
std::unique_ptr< std::mutex >	mutables_ {make_unique<std::mutex>()}
std::shared_ptr< Map< Key, Value > >	primary_
	The primary map.
std::shared_ptr< Map< Key, Value > >	secondary_
	The secondary map.

Detailed Description

template<class Key, class Value, template< class, class > class Map = locking_map>
class meta::caching::dblru_cache< Key, Value, Map >

A double-barrel approach at a LRU cache.

Uses two Maps, primary and secondary, for implementation. A find will search in the primary and, if found, return the found value. Otherwise, it will search the secondary—if found, that value is promoted to the primary map and the value returned. Otherwise, the value does not exist.

After a fixed number of inserts into the primary, the secondary is emptied and swapped with the primary. This ensures that things that have been less recently used are dropped.

It is assumed that the Maps are internally synchronized (i.e., they contain a mutex or have some other way of guaranteeing concurrency safety).

See also

https://issues.apache.org/jira/browse/LUCENE-2075

Constructor & Destructor Documentation

template<class Key , class Value , template< class, class > class Map>

meta::caching::dblru_cache< Key, Value, Map >::dblru_cache

(

uint64_t

max_size

)

Constructs a dlbru_cache with a given fixed size.

Parameters

max_size

the maximum allowed size for this cache

Member Function Documentation

template<class Key , class Value , template< class, class > class Map>

dblru_cache< Key, Value, Map > & meta::caching::dblru_cache< Key, Value, Map >::operator=

(

dblru_cache< Key, Value, Map >

rhs

)

dlbru_cache may be be assigned.

Returns

the current dblru_cache

template<class Key , class Value , template< class, class > class Map>

void meta::caching::dblru_cache< Key, Value, Map >::swap

(

dblru_cache< Key, Value, Map > &

other

)

Swaps the current dlbru_cache with a given one.

Parameters

other

the cache to swap with

template<class Key , class Value , template< class, class > class Map>

void meta::caching::dblru_cache< Key, Value, Map >::insert	(	const Key &	key,
		const Value &	value
	)

Insert a given (key, value) pair into the cache.

Parameters

key
value

template<class Key , class Value , template< class, class > class Map>

template<class... Args>

void meta::caching::dblru_cache< Key, Value, Map >::emplace

(

Args &&...

args

)

Inserts a key value pair into the cache using in-place construction if possible.

Parameters

args	the list of arguments to forward to constructing the (key, value) pair

template<class Key , class Value , template< class, class > class Map>

util::optional< Value > meta::caching::dblru_cache< Key, Value, Map >::find

(

const Key &

key

)

Finds a value in the cache.

If it exists, the optional will be engaged, otherwise, it will be disengaged.

Parameters

key	the key to find the corresponding value for

Returns

an optional that may contain the value, if found

template<class Key , class Value , template< class, class > class Map>

void meta::caching::dblru_cache< Key, Value, Map >::clear

(

)

Empties the cache.

---

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

• /home/chase/projects/meta/include/caching/dblru_cache.h
• /home/chase/projects/meta/include/caching/dblru_cache.tcc