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21
22
23 #ifndef _STOC_SEC_LRU_CACHE_H_
24 #define _STOC_SEC_LRU_CACHE_H_
25
26 #include <hash_map>
27
28 // __CACHE_DIAGNOSE works only for OUString keys
29 #ifdef __CACHE_DIAGNOSE
30 #include <osl/diagnose.h>
31 #include <rtl/ustrbuf.hxx>
32 #include <rtl/ustring.hxx>
33 #include <rtl/string.hxx>
34 #endif
35
36
37 namespace stoc_sec
38 {
39
40 /** Implementation of a least recently used (lru) cache.
41 */
42 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
43 class lru_cache
44 {
45 struct Entry
46 {
47 t_key m_key;
48 t_val m_val;
49 Entry * m_pred;
50 Entry * m_succ;
51 };
52 typedef ::std::hash_map< t_key, Entry *, t_hashKey, t_equalKey > t_key2element;
53 t_key2element m_key2element;
54 ::std::size_t m_size;
55
56 Entry * m_block;
57 mutable Entry * m_head;
58 mutable Entry * m_tail;
59 inline void toFront( Entry * entry ) const SAL_THROW( () );
60
61 public:
62 /** Default Ctor. Does not cache.
63 */
64 inline lru_cache() SAL_THROW( () );
65 /** Ctor.
66
67 @param size number of elements to be cached; default param set to 128
68 */
69 inline lru_cache( ::std::size_t size ) SAL_THROW( () );
70
71 /** Destructor: releases all cached elements and keys.
72 */
73 inline ~lru_cache() SAL_THROW( () );
74
75 /** Retrieves a pointer to value in cache. Returns 0, if none was found.
76
77 @param key a key
78 @return pointer to value or 0
79 */
80 inline t_val const * lookup( t_key const & key ) const SAL_THROW( () );
81
82 /** Sets a value to be cached for given key.
83
84 @param key a key
85 @param val a value
86 */
87 inline void set( t_key const & key, t_val const & val ) SAL_THROW( () );
88
89 /** Tests whether a value is cached for given key.
90
91 @param key a key
92 @return true, if value is cached
93 */
94 inline bool has( t_key const & key ) const SAL_THROW( () );
95
96 /** Clears the cache, releasing all cached elements and keys.
97 */
98 inline void clear() SAL_THROW( () );
99
100 /** Sets the number of elements to be cached. This will clear previous entries.
101
102 @param cacheSize number of elements to be cached
103 */
104 inline void setSize( ::std::size_t size ) SAL_THROW( () );
105 };
106 //__________________________________________________________________________________________________
107 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
setSize(::std::size_t size)108 inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::setSize(
109 ::std::size_t size ) SAL_THROW( () )
110 {
111 m_key2element.clear();
112 delete [] m_block;
113 m_block = 0;
114 m_size = size;
115
116 if (0 < m_size)
117 {
118 m_block = new Entry[ m_size ];
119 m_head = m_block;
120 m_tail = m_block + m_size -1;
121 for ( ::std::size_t nPos = m_size; nPos--; )
122 {
123 m_block[ nPos ].m_pred = m_block + nPos -1;
124 m_block[ nPos ].m_succ = m_block + nPos +1;
125 }
126 }
127 }
128 //__________________________________________________________________________________________________
129 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
lru_cache(::std::size_t size)130 inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lru_cache(
131 ::std::size_t size ) SAL_THROW( () )
132 : m_size( 0 )
133 , m_block( 0 )
134 {
135 setSize( size );
136 }
137 //__________________________________________________________________________________________________
138 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
lru_cache()139 inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lru_cache() SAL_THROW( () )
140 : m_size( 0 )
141 , m_block( 0 )
142 {
143 }
144 //__________________________________________________________________________________________________
145 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
~lru_cache()146 inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::~lru_cache()
147 SAL_THROW( () )
148 {
149 delete [] m_block;
150 }
151 //__________________________________________________________________________________________________
152 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
toFront(Entry * entry) const153 inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::toFront(
154 Entry * entry ) const SAL_THROW( () )
155 {
156 if (entry != m_head)
157 {
158 // cut out element
159 if (entry == m_tail)
160 {
161 m_tail = entry->m_pred;
162 }
163 else
164 {
165 entry->m_succ->m_pred = entry->m_pred;
166 entry->m_pred->m_succ = entry->m_succ;
167 }
168 // push to front
169 m_head->m_pred = entry;
170 entry->m_succ = m_head;
171 m_head = entry;
172 }
173 }
174 //__________________________________________________________________________________________________
175 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
has(t_key const & key) const176 inline bool lru_cache< t_key, t_val, t_hashKey, t_equalKey >::has(
177 t_key const & key ) const SAL_THROW( () )
178 {
179 typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
180 return (iFind != m_key2element.end());
181 }
182 //__________________________________________________________________________________________________
183 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
lookup(t_key const & key) const184 inline t_val const * lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lookup(
185 t_key const & key ) const SAL_THROW( () )
186 {
187 if (0 < m_size)
188 {
189 typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
190 if (iFind != m_key2element.end())
191 {
192 Entry * entry = iFind->second;
193 toFront( entry );
194 #ifdef __CACHE_DIAGNOSE
195 ::rtl::OUStringBuffer buf( 48 );
196 buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("> retrieved element \"") );
197 buf.append( entry->m_key );
198 buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("\" from cache") );
199 ::rtl::OString str( ::rtl::OUStringToOString(
200 buf.makeStringAndClear(), RTL_TEXTENCODING_ASCII_US ) );
201 OSL_TRACE( str.getStr() );
202 #endif
203 return &entry->m_val;
204 }
205 }
206 return 0;
207 }
208 //__________________________________________________________________________________________________
209 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
set(t_key const & key,t_val const & val)210 inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::set(
211 t_key const & key, t_val const & val ) SAL_THROW( () )
212 {
213 if (0 < m_size)
214 {
215 typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
216
217 Entry * entry;
218 if (iFind == m_key2element.end())
219 {
220 entry = m_tail; // erase last element
221 #ifdef __CACHE_DIAGNOSE
222 if (entry->m_key.getLength())
223 {
224 ::rtl::OUStringBuffer buf( 48 );
225 buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("> kicking element \"") );
226 buf.append( entry->m_key );
227 buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("\" from cache") );
228 ::rtl::OString str( ::rtl::OUStringToOString(
229 buf.makeStringAndClear(), RTL_TEXTENCODING_ASCII_US ) );
230 OSL_TRACE( str.getStr() );
231 }
232 #endif
233 m_key2element.erase( entry->m_key );
234 entry->m_key = key;
235 ::std::pair< typename t_key2element::iterator, bool > insertion(
236 m_key2element.insert( typename t_key2element::value_type( key, entry ) ) );
237 #ifdef __CACHE_DIAGNOSE
238 OSL_ENSURE( insertion.second, "### inserting new cache entry failed?!" );
239 #endif
240 }
241 else
242 {
243 entry = iFind->second;
244 #ifdef __CACHE_DIAGNOSE
245 ::rtl::OUStringBuffer buf( 48 );
246 buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("> replacing element \"") );
247 buf.append( entry->m_key );
248 buf.appendAscii( RTL_CONSTASCII_STRINGPARAM("\" in cache") );
249 ::rtl::OString str( ::rtl::OUStringToOString(
250 buf.makeStringAndClear(), RTL_TEXTENCODING_ASCII_US ) );
251 OSL_TRACE( str.getStr() );
252 #endif
253 }
254 entry->m_val = val;
255 toFront( entry );
256 }
257 }
258 //__________________________________________________________________________________________________
259 template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
clear()260 inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::clear() SAL_THROW( () )
261 {
262 m_key2element.clear();
263 for ( ::std::size_t nPos = m_size; nPos--; )
264 {
265 m_block[ nPos ].m_key = t_key();
266 m_block[ nPos ].m_val = t_val();
267 }
268 #ifdef __CACHE_DIAGNOSE
269 OSL_TRACE( "> cleared cache\n" );
270 #endif
271 }
272
273 }
274
275 #endif
276