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1 /**************************************************************************
2  *
3  * Copyright 2008 VMware, Inc.
4  * All Rights Reserved.
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining a
7  * copy of this software and associated documentation files (the
8  * "Software"), to deal in the Software without restriction, including
9  * without limitation the rights to use, copy, modify, merge, publish,
10  * distribute, sub license, and/or sell copies of the Software, and to
11  * permit persons to whom the Software is furnished to do so, subject to
12  * the following conditions:
13  *
14  * The above copyright notice and this permission notice (including the
15  * next paragraph) shall be included in all copies or substantial portions
16  * of the Software.
17  *
18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
19  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
21  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
25  *
26  **************************************************************************/
27 
28 /**
29  * @file
30  * Improved cache implementation.
31  *
32  * Fixed size array with linear probing on collision and LRU eviction
33  * on full.
34  *
35  * @author Jose Fonseca <jfonseca@vmware.com>
36  */
37 
38 
39 #include "pipe/p_compiler.h"
40 #include "util/u_debug.h"
41 
42 #include "util/u_math.h"
43 #include "util/u_memory.h"
44 #include "util/u_cache.h"
45 #include "util/u_simple_list.h"
46 
47 
48 struct util_cache_entry
49 {
50    enum { EMPTY = 0, FILLED, DELETED } state;
51    uint32_t hash;
52 
53    struct util_cache_entry *next;
54    struct util_cache_entry *prev;
55 
56    void *key;
57    void *value;
58 
59 #ifdef DEBUG
60    unsigned count;
61 #endif
62 };
63 
64 
65 struct util_cache
66 {
67    /** Hash function */
68    uint32_t (*hash)(const void *key);
69 
70    /** Compare two keys */
71    int (*compare)(const void *key1, const void *key2);
72 
73    /** Destroy a (key, value) pair */
74    void (*destroy)(void *key, void *value);
75 
76    uint32_t size;
77 
78    struct util_cache_entry *entries;
79 
80    unsigned count;
81    struct util_cache_entry lru;
82 };
83 
84 static void
85 ensure_sanity(const struct util_cache *cache);
86 
87 #define CACHE_DEFAULT_ALPHA 2
88 
89 struct util_cache *
util_cache_create(uint32_t (* hash)(const void * key),int (* compare)(const void * key1,const void * key2),void (* destroy)(void * key,void * value),uint32_t size)90 util_cache_create(uint32_t (*hash)(const void *key),
91                   int (*compare)(const void *key1, const void *key2),
92                   void (*destroy)(void *key, void *value),
93                   uint32_t size)
94 {
95    struct util_cache *cache;
96 
97    cache = CALLOC_STRUCT(util_cache);
98    if(!cache)
99       return NULL;
100 
101    cache->hash = hash;
102    cache->compare = compare;
103    cache->destroy = destroy;
104 
105    make_empty_list(&cache->lru);
106 
107    size *= CACHE_DEFAULT_ALPHA;
108    cache->size = size;
109 
110    cache->entries = CALLOC(size, sizeof(struct util_cache_entry));
111    if(!cache->entries) {
112       FREE(cache);
113       return NULL;
114    }
115 
116    ensure_sanity(cache);
117    return cache;
118 }
119 
120 
121 static struct util_cache_entry *
util_cache_entry_get(struct util_cache * cache,uint32_t hash,const void * key)122 util_cache_entry_get(struct util_cache *cache,
123                      uint32_t hash,
124                      const void *key)
125 {
126    struct util_cache_entry *first_unfilled = NULL;
127    uint32_t index = hash % cache->size;
128    uint32_t probe;
129 
130    /* Probe until we find either a matching FILLED entry or an EMPTY
131     * slot (which has never been occupied).
132     *
133     * Deleted or non-matching slots are not indicative of completion
134     * as a previous linear probe for the same key could have continued
135     * past this point.
136     */
137    for (probe = 0; probe < cache->size; probe++) {
138       uint32_t i = (index + probe) % cache->size;
139       struct util_cache_entry *current = &cache->entries[i];
140 
141       if (current->state == FILLED) {
142          if (current->hash == hash &&
143              cache->compare(key, current->key) == 0)
144             return current;
145       }
146       else {
147          if (!first_unfilled)
148             first_unfilled = current;
149 
150          if (current->state == EMPTY)
151             return first_unfilled;
152       }
153    }
154 
155    return NULL;
156 }
157 
158 static INLINE void
util_cache_entry_destroy(struct util_cache * cache,struct util_cache_entry * entry)159 util_cache_entry_destroy(struct util_cache *cache,
160                          struct util_cache_entry *entry)
161 {
162    void *key = entry->key;
163    void *value = entry->value;
164 
165    entry->key = NULL;
166    entry->value = NULL;
167 
168    if (entry->state == FILLED) {
169       remove_from_list(entry);
170       cache->count--;
171 
172       if(cache->destroy)
173          cache->destroy(key, value);
174 
175       entry->state = DELETED;
176    }
177 }
178 
179 
180 void
util_cache_set(struct util_cache * cache,void * key,void * value)181 util_cache_set(struct util_cache *cache,
182                void *key,
183                void *value)
184 {
185    struct util_cache_entry *entry;
186    uint32_t hash = cache->hash(key);
187 
188    assert(cache);
189    if (!cache)
190       return;
191 
192    entry = util_cache_entry_get(cache, hash, key);
193    if (!entry)
194       entry = cache->lru.prev;
195 
196    if (cache->count >= cache->size / CACHE_DEFAULT_ALPHA)
197       util_cache_entry_destroy(cache, cache->lru.prev);
198 
199    util_cache_entry_destroy(cache, entry);
200 
201 #ifdef DEBUG
202    ++entry->count;
203 #endif
204 
205    entry->key = key;
206    entry->hash = hash;
207    entry->value = value;
208    entry->state = FILLED;
209    insert_at_head(&cache->lru, entry);
210    cache->count++;
211 
212    ensure_sanity(cache);
213 }
214 
215 
216 void *
util_cache_get(struct util_cache * cache,const void * key)217 util_cache_get(struct util_cache *cache,
218                const void *key)
219 {
220    struct util_cache_entry *entry;
221    uint32_t hash = cache->hash(key);
222 
223    assert(cache);
224    if (!cache)
225       return NULL;
226 
227    entry = util_cache_entry_get(cache, hash, key);
228    if (!entry)
229       return NULL;
230 
231    if (entry->state == FILLED)
232       move_to_head(&cache->lru, entry);
233 
234    return entry->value;
235 }
236 
237 
238 void
util_cache_clear(struct util_cache * cache)239 util_cache_clear(struct util_cache *cache)
240 {
241    uint32_t i;
242 
243    assert(cache);
244    if (!cache)
245       return;
246 
247    for(i = 0; i < cache->size; ++i) {
248       util_cache_entry_destroy(cache, &cache->entries[i]);
249       cache->entries[i].state = EMPTY;
250    }
251 
252    assert(cache->count == 0);
253    assert(is_empty_list(&cache->lru));
254    ensure_sanity(cache);
255 }
256 
257 
258 void
util_cache_destroy(struct util_cache * cache)259 util_cache_destroy(struct util_cache *cache)
260 {
261    assert(cache);
262    if (!cache)
263       return;
264 
265 #ifdef DEBUG
266    if(cache->count >= 20*cache->size) {
267       /* Normal approximation of the Poisson distribution */
268       double mean = (double)cache->count/(double)cache->size;
269       double stddev = sqrt(mean);
270       unsigned i;
271       for(i = 0; i < cache->size; ++i) {
272          double z = fabs(cache->entries[i].count - mean)/stddev;
273          /* This assert should not fail 99.9999998027% of the times, unless
274           * the hash function is a poor one */
275          assert(z <= 6.0);
276       }
277    }
278 #endif
279 
280    util_cache_clear(cache);
281 
282    FREE(cache->entries);
283    FREE(cache);
284 }
285 
286 
287 void
util_cache_remove(struct util_cache * cache,const void * key)288 util_cache_remove(struct util_cache *cache,
289                   const void *key)
290 {
291    struct util_cache_entry *entry;
292    uint32_t hash;
293 
294    assert(cache);
295    if (!cache)
296       return;
297 
298    hash = cache->hash(key);
299 
300    entry = util_cache_entry_get(cache, hash, key);
301    if (!entry)
302       return;
303 
304    if (entry->state == FILLED)
305       util_cache_entry_destroy(cache, entry);
306 
307    ensure_sanity(cache);
308 }
309 
310 
311 static void
ensure_sanity(const struct util_cache * cache)312 ensure_sanity(const struct util_cache *cache)
313 {
314 #ifdef DEBUG
315    unsigned i, cnt = 0;
316 
317    assert(cache);
318    for (i = 0; i < cache->size; i++) {
319       struct util_cache_entry *header = &cache->entries[i];
320 
321       assert(header);
322       assert(header->state == FILLED ||
323              header->state == EMPTY ||
324              header->state == DELETED);
325       if (header->state == FILLED) {
326          cnt++;
327          assert(header->hash == cache->hash(header->key));
328       }
329    }
330 
331    assert(cnt == cache->count);
332    assert(cache->size >= cnt);
333 
334    if (cache->count == 0) {
335       assert (is_empty_list(&cache->lru));
336    }
337    else {
338       struct util_cache_entry *header = cache->lru.next;
339 
340       assert (header);
341       assert (!is_empty_list(&cache->lru));
342 
343       for (i = 0; i < cache->count; i++)
344          header = header->next;
345 
346       assert(header == &cache->lru);
347    }
348 #endif
349 
350    (void)cache;
351 }
352