277 lines
8.3 KiB
C++
277 lines
8.3 KiB
C++
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/*
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* This file is part of the LibreOffice project.
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* This file incorporates work covered by the following license notice:
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed
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* with this work for additional information regarding copyright
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* ownership. The ASF licenses this file to you under the Apache
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* License, Version 2.0 (the "License"); you may not use this file
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* except in compliance with the License. You may obtain a copy of
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* the License at http://www.apache.org/licenses/LICENSE-2.0 .
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*/
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#ifndef INCLUDED_STOC_SOURCE_SECURITY_LRU_CACHE_H
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#define INCLUDED_STOC_SOURCE_SECURITY_LRU_CACHE_H
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#include <unordered_map>
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// __CACHE_DIAGNOSE works only for OUString keys
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#ifdef __CACHE_DIAGNOSE
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#include <osl/diagnose.h>
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#include <rtl/ustrbuf.hxx>
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#include <rtl/ustring.hxx>
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#include <rtl/string.hxx>
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#endif
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namespace stoc_sec
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{
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/** Implementation of a least recently used (lru) cache.
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*/
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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class lru_cache
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{
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struct Entry
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{
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t_key m_key;
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t_val m_val;
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Entry * m_pred;
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Entry * m_succ;
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};
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typedef std::unordered_map< t_key, Entry *, t_hashKey, t_equalKey > t_key2element;
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t_key2element m_key2element;
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::std::size_t m_size;
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Entry * m_block;
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mutable Entry * m_head;
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mutable Entry * m_tail;
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inline void toFront( Entry * entry ) const;
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public:
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/** Default Ctor. Does not cache.
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*/
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inline lru_cache();
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/** Ctor.
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@param size number of elements to be cached; default param set to 128
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*/
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inline lru_cache( ::std::size_t size );
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/** Destructor: releases all cached elements and keys.
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*/
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inline ~lru_cache();
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/** Retrieves a pointer to value in cache. Returns 0, if none was found.
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@param key a key
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@return pointer to value or 0
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*/
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inline t_val const * lookup( t_key const & key ) const;
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/** Sets a value to be cached for given key.
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@param key a key
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@param val a value
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*/
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inline void set( t_key const & key, t_val const & val );
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/** Tests whether a value is cached for given key.
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@param key a key
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@return true, if value is cached
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*/
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inline bool has( t_key const & key ) const;
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/** Clears the cache, releasing all cached elements and keys.
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*/
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inline void clear();
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/** Sets the number of elements to be cached. This will clear previous entries.
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@param cacheSize number of elements to be cached
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*/
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inline void setSize( ::std::size_t size );
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};
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::setSize(
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::std::size_t size )
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{
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m_key2element.clear();
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delete [] m_block;
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m_block = 0;
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m_size = size;
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if (0 < m_size)
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{
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m_block = new Entry[ m_size ];
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m_head = m_block;
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m_tail = m_block + m_size -1;
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for ( ::std::size_t nPos = m_size; nPos--; )
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{
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m_block[ nPos ].m_pred = m_block + nPos -1;
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m_block[ nPos ].m_succ = m_block + nPos +1;
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}
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}
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lru_cache(
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::std::size_t size )
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: m_size( 0 )
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, m_block( 0 )
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, m_tail( 0 )
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{
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setSize( size );
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lru_cache()
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: m_size( 0 )
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, m_block( 0 )
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, m_head( 0 )
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, m_tail( 0 )
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{
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::~lru_cache()
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{
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delete [] m_block;
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::toFront(
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Entry * entry ) const
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{
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if (entry != m_head)
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{
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// cut out element
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if (entry == m_tail)
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{
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m_tail = entry->m_pred;
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}
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else
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{
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entry->m_succ->m_pred = entry->m_pred;
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entry->m_pred->m_succ = entry->m_succ;
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}
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// push to front
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m_head->m_pred = entry;
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entry->m_succ = m_head;
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m_head = entry;
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}
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline bool lru_cache< t_key, t_val, t_hashKey, t_equalKey >::has(
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t_key const & key ) const
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{
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typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
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return (iFind != m_key2element.end());
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline t_val const * lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lookup(
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t_key const & key ) const
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{
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if (0 < m_size)
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{
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typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
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if (iFind != m_key2element.end())
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{
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Entry * entry = iFind->second;
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toFront( entry );
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#ifdef __CACHE_DIAGNOSE
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OUStringBuffer buf( 48 );
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buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("> retrieved element \"") );
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buf.append( entry->m_key );
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buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("\" from cache") );
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OString str( OUStringToOString(
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buf.makeStringAndClear(), RTL_TEXTENCODING_ASCII_US ) );
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OSL_TRACE( "%s", str.getStr() );
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#endif
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return &entry->m_val;
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}
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}
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return 0;
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::set(
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t_key const & key, t_val const & val )
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{
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if (0 < m_size)
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{
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typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
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Entry * entry;
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if (iFind == m_key2element.end())
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{
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entry = m_tail; // erase last element
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#ifdef __CACHE_DIAGNOSE
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if (entry->m_key.getLength())
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{
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OUStringBuffer buf( 48 );
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buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("> kicking element \"") );
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buf.append( entry->m_key );
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buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("\" from cache") );
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OString str( OUStringToOString(
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buf.makeStringAndClear(), RTL_TEXTENCODING_ASCII_US ) );
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OSL_TRACE( "%s", str.getStr() );
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}
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#endif
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m_key2element.erase( entry->m_key );
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entry->m_key = key;
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::std::pair< typename t_key2element::iterator, bool > insertion(
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m_key2element.insert( typename t_key2element::value_type( key, entry ) ) );
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#ifdef __CACHE_DIAGNOSE
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OSL_ENSURE( insertion.second, "### inserting new cache entry failed?!" );
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#endif
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(void) insertion; // avoid warnings
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}
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else
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{
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entry = iFind->second;
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#ifdef __CACHE_DIAGNOSE
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OUStringBuffer buf( 48 );
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buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("> replacing element \"") );
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buf.append( entry->m_key );
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buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("\" in cache") );
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OString str( OUStringToOString(
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buf.makeStringAndClear(), RTL_TEXTENCODING_ASCII_US ) );
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OSL_TRACE( "%s", str.getStr() );
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#endif
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}
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entry->m_val = val;
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toFront( entry );
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}
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}
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template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
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inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::clear()
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{
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m_key2element.clear();
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for ( ::std::size_t nPos = m_size; nPos--; )
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{
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m_block[ nPos ].m_key = t_key();
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m_block[ nPos ].m_val = t_val();
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}
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#ifdef __CACHE_DIAGNOSE
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OSL_TRACE( "> cleared cache" );
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#endif
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}
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}
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#endif
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/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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