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Diffstat (limited to 'stoc/source/corereflection/lrucache.hxx')
| -rw-r--r-- | stoc/source/corereflection/lrucache.hxx | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/stoc/source/corereflection/lrucache.hxx b/stoc/source/corereflection/lrucache.hxx new file mode 100644 index 000000000..d5eebe804 --- /dev/null +++ b/stoc/source/corereflection/lrucache.hxx @@ -0,0 +1,209 @@ +/* -*- 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: */ |