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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* This file incorporates work covered by the following license notice:
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed
* with this work for additional information regarding copyright
* ownership. The ASF licenses this file to you under the Apache
* License, Version 2.0 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.apache.org/licenses/LICENSE-2.0 .
*/
#ifndef INCLUDED_STOC_SOURCE_COREREFLECTION_LRUCACHE_HXX
#define INCLUDED_STOC_SOURCE_COREREFLECTION_LRUCACHE_HXX
// __CACHE_DIAGNOSE forces cache size to 4 and works only for OUString keys
// #define __CACHE_DIAGNOSE 1
#include <rtl/ustring.hxx>
#include <memory>
#include <mutex>
#include <unordered_map>
namespace com::sun::star::uno { class Any; }
/** Implementation of a least recently used (lru) cache.
<br>
*/
template< class t_Key, class t_Val, class t_KeyHash >
class LRU_Cache
{
struct CacheEntry
{
t_Key aKey;
t_Val aVal;
CacheEntry * pPred;
CacheEntry * pSucc;
};
typedef std::unordered_map< t_Key, CacheEntry *, t_KeyHash > t_Key2Element;
mutable std::mutex _aCacheMutex;
sal_Int32 _nCachedElements;
t_Key2Element _aKey2Element;
std::unique_ptr<CacheEntry[]> _pBlock;
mutable CacheEntry * _pHead;
mutable CacheEntry * _pTail;
inline void toFront( CacheEntry * pEntry ) const;
public:
/** Constructor:
<br>
@param nCachedElements number of elements to be cached; default param set to 128
*/
explicit inline LRU_Cache();
/** Retrieves a value from the cache. Returns default constructed value,
if none was found.
<br>
@param rKey a key
@return value
*/
inline t_Val getValue( const t_Key & rKey ) const;
/** Sets a value to be cached for given key.
<br>
@param rKey a key
@param rValue a value
*/
inline void setValue( const t_Key & rKey, const t_Val & rValue );
/** Clears the cache, thus releasing all cached elements and keys.
<br>
*/
inline void clear();
};
template< class t_Key, class t_Val, class t_KeyHash >
inline LRU_Cache< t_Key, t_Val, t_KeyHash >::LRU_Cache()
#ifdef __CACHE_DIAGNOSE
: _nCachedElements( 4 )
#else
: _nCachedElements( 256 )
#endif
, _pBlock( nullptr )
, _pHead( nullptr )
, _pTail( nullptr )
{
_pBlock.reset(new CacheEntry[_nCachedElements]);
_pHead = _pBlock.get();
_pTail = _pBlock.get() + _nCachedElements - 1;
for (sal_Int32 nPos = _nCachedElements; nPos--;)
{
_pBlock[nPos].pPred = _pBlock.get() + nPos - 1;
_pBlock[nPos].pSucc = _pBlock.get() + nPos + 1;
}
}
template< class t_Key, class t_Val, class t_KeyHash >
inline void LRU_Cache< t_Key, t_Val, t_KeyHash >::toFront( CacheEntry * pEntry ) const
{
if (pEntry != _pHead)
{
// cut out element
if (pEntry == _pTail)
{
_pTail = pEntry->pPred;
}
else
{
pEntry->pSucc->pPred = pEntry->pPred;
pEntry->pPred->pSucc = pEntry->pSucc;
}
// push to front
_pHead->pPred = pEntry;
pEntry->pSucc = _pHead;
_pHead = pEntry;
}
}
template< class t_Key, class t_Val, class t_KeyHash >
inline t_Val LRU_Cache< t_Key, t_Val, t_KeyHash >::getValue( const t_Key & rKey ) const
{
std::scoped_lock aGuard( _aCacheMutex );
const typename t_Key2Element::const_iterator iFind( _aKey2Element.find( rKey ) );
if (iFind != _aKey2Element.end())
{
CacheEntry * pEntry = (*iFind).second;
toFront( pEntry );
#ifdef __CACHE_DIAGNOSE
SAL_INFO("stoc.corerefl", "> retrieved element \"" );
SAL_INFO("stoc.corerefl", "" << pEntry->aKey);
SAL_INFO("stoc.corerefl", "\" from cache <" );
#endif
return pEntry->aVal;
}
return t_Val();
}
template< class t_Key, class t_Val, class t_KeyHash >
inline void LRU_Cache< t_Key, t_Val, t_KeyHash >::setValue(
const t_Key & rKey, const t_Val & rValue )
{
std::scoped_lock aGuard( _aCacheMutex );
if (_nCachedElements > 0)
{
const typename t_Key2Element::const_iterator iFind( _aKey2Element.find( rKey ) );
CacheEntry * pEntry;
if (iFind == _aKey2Element.end())
{
pEntry = _pTail; // erase last element
#ifdef __CACHE_DIAGNOSE
if (pEntry->aKey.getLength())
{
SAL_INFO("stoc.corerefl", "> kicking element \"" );
SAL_INFO("stoc.corerefl", "" << pEntry->aKey);
SAL_INFO("stoc.corerefl", "\" from cache <" );
}
#endif
_aKey2Element.erase( pEntry->aKey );
pEntry->aKey = rKey;
_aKey2Element[ rKey ] = pEntry;
}
else
{
pEntry = (*iFind).second;
#ifdef __CACHE_DIAGNOSE
SAL_INFO("stoc.corerefl", "> replacing element \"" );
SAL_INFO("stoc.corerefl", "" << pEntry->aKey);
SAL_INFO("stoc.corerefl", "\" in cache <" );
#endif
}
pEntry->aVal = rValue;
toFront( pEntry );
}
}
template< class t_Key, class t_Val, class t_KeyHash >
inline void LRU_Cache< t_Key, t_Val, t_KeyHash >::clear()
{
std::scoped_lock aGuard( _aCacheMutex );
_aKey2Element.clear();
for ( sal_Int32 nPos = _nCachedElements; nPos--; )
{
_pBlock[nPos].aKey = t_Key();
_pBlock[nPos].aVal = t_Val();
}
_nCachedElements = 0;
#ifdef __CACHE_DIAGNOSE
SAL_INFO("stoc.corerefl", "> cleared cache <" );
#endif
}
/** Template instance for OUString keys, Any values.<br>
*/
typedef LRU_Cache< OUString, css::uno::Any, OUStringHash >
LRU_CacheAnyByOUString;
#endif
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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