vmap/libs/container/cache.h

/*
   Copyright (C) 2001-2006, William Joseph.
   All Rights Reserved.

   This file is part of GtkRadiant.

   GtkRadiant is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   GtkRadiant is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with GtkRadiant; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#if !defined( INCLUDED_CONTAINER_CACHE_H )
#define INCLUDED_CONTAINER_CACHE_H

#include <cstddef>
#include "container/hashtable.h"
#include "memory/allocator.h"

template<typename Type, typename Parameter>
class DefaultCreationPolicy
{
public:
Type* construct( const Parameter& parameter ){
	return New<Type>().scalar( parameter );
}
void destroy( Type* p ){
	Delete<Type>().scalar( p );
}
};

template<typename Type>
class SharedValue
{
typedef Type value_type;
typedef value_type* pointer;
typedef value_type& reference;

std::size_t m_count;
pointer m_value;

public:
SharedValue()
	: m_count( 0 ), m_value( 0 ){
}
~SharedValue(){
	ASSERT_MESSAGE( m_count == 0, "destroying a referenced object\n" );
}
void set( pointer value ){
	m_value = value;
}
pointer get(){
	return m_value;
}
std::size_t increment(){
	return ++m_count;
}
std::size_t decrement(){
	ASSERT_MESSAGE( !empty(), "destroying a non-existent object\n" );
	return --m_count;
}
std::size_t count(){
	return m_count;
}
bool empty(){
	return m_count == 0;
}
reference operator*() const {
	ASSERT_NOTNULL( m_value );
	return *m_value;
}
pointer operator->() const {
	return &( operator*() );
}
};



/// \brief Caches values that are uniquely identified by a key.
///
/// - Automatically removes objects that are no longer referenced.
///
/// \param Key Uniquely identifies each element.
/// \param Cached The type to be cached. Must define a constructor that accepts \c Key.
/// \param CreationPolicy Must define 'Cached* construct(const Key&)' and 'void destroy(Cached*)'. The lifetime of the \c Key passed to 'construct' is guaranteed to be longer than the subsequent matched call to 'destroy'.
template<typename Key, typename Cached, typename Hasher, typename KeyEqual = std::equal_to<Key>, typename CreationPolicy = DefaultCreationPolicy<Cached, Key> >
class HashedCache : public CreationPolicy
{
typedef SharedValue<Cached> Element;
typedef HashTable<Key, Element, Hasher, KeyEqual> map_type;

map_type m_map;

public:
explicit HashedCache( const CreationPolicy& creation = CreationPolicy() )
	: CreationPolicy( creation ), m_map( 256 ){
}
~HashedCache(){
	ASSERT_MESSAGE( empty(), "HashedCache::~HashedCache: not empty" );
}

typedef typename map_type::iterator iterator;
typedef typename map_type::value_type value_type;

iterator begin(){
	return m_map.begin();
}
iterator end(){
	return m_map.end();
}

bool empty() const {
	return m_map.empty();
}

iterator find( const Key& key ){
	return m_map.find( key );
}

void capture( iterator i ){
	( *i ).value.increment();
}
void release( iterator i ){
	if ( ( *i ).value.decrement() == 0 ) {
		CreationPolicy::destroy( ( *i ).value.get() );
		m_map.erase( i );
	}
}

#if 1
Element& capture( const Key& key ){
#if 0
	Element& elem = m_map[key];
	if ( elem.increment() == 1 ) {
		elem.set( CreationPolicy::construct( key ) );
	}
	return elem;
#else
	iterator i = m_map.insert( key, Element() );
	if ( ( *i ).value.increment() == 1 ) {
		( *i ).value.set( CreationPolicy::construct( ( *i ).key ) );
	}
	return ( *i ).value;
#endif
}
#else
value_type& capture( const Key& key ){
	iterator i = m_map.find( key );
	if ( i == m_map.end() ) {
		i = m_map.insert( key, Element() );
		( *i ).value.set( CreationPolicy::construct( ( *i ).key ) );
	}
	( *i ).value.increment();
	return ( *i );
}
#endif
void release( const Key& key ){
	iterator i = m_map.find( key );
	ASSERT_MESSAGE( i != m_map.end(), "releasing a non-existent object\n" );
	release( i );
}

void clear(){
	m_map.clear();
}
};


#endif