osmscout::Cache< K, V, IK > Class Template Reference

Generic FIFO cache implementation with O(n log n) semantic. More...

#include <Cache.h>

Classes
struct	CacheEntry
	An individual entry in the cache. More...
class	ValueSizer
	ValueSizer returns the size (in bytes) of an individual cache value. More...

Public Types
using	CacheRef = typename OrderList::iterator
using	Map = std::unordered_map< K, typename OrderList::iterator >
using	OrderList = std::list< CacheEntry >

Public Member Functions
	Cache (size_t maxSize)
	Create a new cache object with the given max size.
void	DumpStatistics (const char *cacheName, const ValueSizer &sizer)
	Dump some cache statistics to std::cout.
void	Flush ()
	Completely flush the cache removing all entries from it.
bool	GetEntry (const K &key, CacheRef &reference)
	Getting the value with the given key from cache.
size_t	GetMaxSize () const
	Returns the maximum size of the cache.
size_t	GetMemory (const ValueSizer &sizer) const
size_t	GetSize () const
	Returns the current size of the cache.
bool	IsActive () const
	Returns if the cache is active (maxSize > 0)
Cache::CacheRef	SetEntry (const CacheEntry &entry)
	Set or update the cache with the given value for the given key.
void	SetMaxSize (size_t maxSize)
	Set a new cache max size, possible striping the oldest entries from cache if the new size is smaller than the old one.

Detailed Description

template<class K, class V, class IK = PageId>
class osmscout::Cache< K, V, IK >

Generic FIFO cache implementation with O(n log n) semantic.

Template parameter class K holds the key value (must be a numerical value), parameter class V holds the data class that is to be cached, and parameter IK holds the internal key value, must be an unsigned value, default is PageId.

• The cache is not threadsafe.
• It uses a std::vector<std::list>> as a hash table for data lookup
• It uses an std::list for implementing FIFO characteristics.

Implementation details: If std::unordered_map ist available we use this for fast detection (O(1)) if an object is already in the cast. If it is not available, we use a vector as a hashtable via the key value with list as entry type for hash code conflict handling.

Member Typedef Documentation

CacheRef

template<class K , class V , class IK = PageId>

using osmscout::Cache< K, V, IK >::CacheRef = typename OrderList::iterator

Map

template<class K , class V , class IK = PageId>

using osmscout::Cache< K, V, IK >::Map = std::unordered_map<K, typename OrderList::iterator>

OrderList

template<class K , class V , class IK = PageId>

using osmscout::Cache< K, V, IK >::OrderList = std::list<CacheEntry>

Constructor & Destructor Documentation

Cache()

template<class K , class V , class IK = PageId>

osmscout::Cache< K, V, IK >::Cache ( size_t  maxSize )

inlineexplicit

Create a new cache object with the given max size.

Member Function Documentation

DumpStatistics()

template<class K , class V , class IK = PageId>

void osmscout::Cache< K, V, IK >::DumpStatistics ( const char *  cacheName, const ValueSizer &  sizer  )

inline

Dump some cache statistics to std::cout.

References osmscout::Log::Debug(), osmscout::Cache< K, V, IK >::GetMemory(), and osmscout::log.

Referenced by osmscout::AreaAreaIndex::DumpStatistics().

Flush()

template<class K , class V , class IK = PageId>

void osmscout::Cache< K, V, IK >::Flush ( )

inline

Completely flush the cache removing all entries from it.

Referenced by osmscout::AreaAreaIndex::Close(), and osmscout::AreaAreaIndex::FlushCache().

GetEntry()

template<class K , class V , class IK = PageId>

bool osmscout::Cache< K, V, IK >::GetEntry ( const K &  key, CacheRef &  reference  )

inline

Getting the value with the given key from cache.

If there is no valued stored with the given key, false will be returned and the reference will be untouched.

If there is a value with the given key, reference will return a reference to the value and the value will moved to the front position of the cache to assure FIFO behaviour.

References osmscout::Cache< K, V, IK >::IsActive().

GetMaxSize()

template<class K , class V , class IK = PageId>

size_t osmscout::Cache< K, V, IK >::GetMaxSize ( ) const

inline

Returns the maximum size of the cache.

GetMemory()

template<class K , class V , class IK = PageId>

size_t osmscout::Cache< K, V, IK >::GetMemory ( const ValueSizer &  sizer ) const

inline

References osmscout::Cache< K, V, IK >::ValueSizer::GetSize().

Referenced by osmscout::Cache< K, V, IK >::DumpStatistics().

GetSize()

template<class K , class V , class IK = PageId>

size_t osmscout::Cache< K, V, IK >::GetSize ( ) const

inline

Returns the current size of the cache.

IsActive()

template<class K , class V , class IK = PageId>

bool osmscout::Cache< K, V, IK >::IsActive ( ) const

inline

Returns if the cache is active (maxSize > 0)

Referenced by osmscout::Cache< K, V, IK >::GetEntry(), and osmscout::Cache< K, V, IK >::SetEntry().

SetEntry()

template<class K , class V , class IK = PageId>

Cache::CacheRef osmscout::Cache< K, V, IK >::SetEntry ( const CacheEntry &  entry )

inline

Set or update the cache with the given value for the given key.

If the key is not available in the cache the value will be added to the front of the cache (FIFO semantic) else the value will be updated (also moving it to the front of the cache (FIFO again).

References osmscout::Cache< K, V, IK >::IsActive(), osmscout::Cache< K, V, IK >::CacheEntry::key, and osmscout::Cache< K, V, IK >::CacheEntry::value.

SetMaxSize()

template<class K , class V , class IK = PageId>

void osmscout::Cache< K, V, IK >::SetMaxSize ( size_t  maxSize )

inline

Set a new cache max size, possible striping the oldest entries from cache if the new size is smaller than the old one.

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

• Cache.h