src/gallium/auxiliary/util/u_cache.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2008 VMware, Inc.
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   7  * copy of this software and associated documentation files (the
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  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
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  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/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    /** Max entries in the cache */
  77    uint32_t size;
  78
  79    /** Array [size] of entries */
  80    struct util_cache_entry *entries;
  81
  82    /** Number of entries in the cache */
  83    unsigned count;
  84
  85    /** Head of list, sorted from Least-recently used to Most-recently used */
  86    struct util_cache_entry lru;
  87 };
  88
  89
  90 static void
  91 ensure_sanity(const struct util_cache *cache);
  92
  93 #define CACHE_DEFAULT_ALPHA 2
  94
  95 /**
  96  * Create a new cache with 'size' entries.  Also provide functions for
  97  * hashing keys, comparing keys and destroying (key,value) pairs.
  98  */
  99 struct util_cache *
 100 util_cache_create(uint32_t (*hash)(const void *key),
 101                   int (*compare)(const void *key1, const void *key2),
 102                   void (*destroy)(void *key, void *value),
 103                   uint32_t size)
 104 {
 105    struct util_cache *cache;
 106
 107    cache = CALLOC_STRUCT(util_cache);
 108    if (!cache)
 109       return NULL;
 110
 111    cache->hash = hash;
 112    cache->compare = compare;
 113    cache->destroy = destroy;
 114
 115    make_empty_list(&cache->lru);
 116
 117    size *= CACHE_DEFAULT_ALPHA;
 118    cache->size = size;
 119
 120    cache->entries = CALLOC(size, sizeof(struct util_cache_entry));
 121    if (!cache->entries) {
 122       FREE(cache);
 123       return NULL;
 124    }
 125
 126    ensure_sanity(cache);
 127    return cache;
 128 }
 129
 130
 131 /**
 132  * Try to find a cache entry, given the key and hash of the key.
 133  */
 134 static struct util_cache_entry *
 135 util_cache_entry_get(struct util_cache *cache,
 136                      uint32_t hash,
 137                      const void *key)
 138 {
 139    struct util_cache_entry *first_unfilled = NULL;
 140    uint32_t index = hash % cache->size;
 141    uint32_t probe;
 142
 143    /* Probe until we find either a matching FILLED entry or an EMPTY
 144     * slot (which has never been occupied).
 145     *
 146     * Deleted or non-matching slots are not indicative of completion
 147     * as a previous linear probe for the same key could have continued
 148     * past this point.
 149     */
 150    for (probe = 0; probe < cache->size; probe++) {
 151       uint32_t i = (index + probe) % cache->size;
 152       struct util_cache_entry *current = &cache->entries[i];
 153
 154       if (current->state == FILLED) {
 155          if (current->hash == hash &&
 156              cache->compare(key, current->key) == 0)
 157             return current;
 158       }
 159       else {
 160          if (!first_unfilled)
 161             first_unfilled = current;
 162
 163          if (current->state == EMPTY)
 164             return first_unfilled;
 165       }
 166    }
 167
 168    return NULL;
 169 }
 170
 171 static inline void
 172 util_cache_entry_destroy(struct util_cache *cache,
 173                          struct util_cache_entry *entry)
 174 {
 175    void *key = entry->key;
 176    void *value = entry->value;
 177
 178    entry->key = NULL;
 179    entry->value = NULL;
 180
 181    if (entry->state == FILLED) {
 182       remove_from_list(entry);
 183       cache->count--;
 184
 185       if (cache->destroy)
 186          cache->destroy(key, value);
 187
 188       entry->state = DELETED;
 189    }
 190 }
 191
 192
 193 /**
 194  * Insert an entry in the cache, given the key and value.
 195  */
 196 void
 197 util_cache_set(struct util_cache *cache,
 198                void *key,
 199                void *value)
 200 {
 201    struct util_cache_entry *entry;
 202    uint32_t hash;
 203
 204    assert(cache);
 205    if (!cache)
 206       return;
 207    hash = cache->hash(key);
 208    entry = util_cache_entry_get(cache, hash, key);
 209    if (!entry)
 210       entry = cache->lru.prev;
 211
 212    if (cache->count >= cache->size / CACHE_DEFAULT_ALPHA)
 213       util_cache_entry_destroy(cache, cache->lru.prev);
 214
 215    util_cache_entry_destroy(cache, entry);
 216
 217 #ifdef DEBUG
 218    ++entry->count;
 219 #endif
 220
 221    entry->key = key;
 222    entry->hash = hash;
 223    entry->value = value;
 224    entry->state = FILLED;
 225    insert_at_head(&cache->lru, entry);
 226    cache->count++;
 227
 228    ensure_sanity(cache);
 229 }
 230
 231
 232 /**
 233  * Search the cache for an entry with the given key.  Return the corresponding
 234  * value or NULL if not found.
 235  */
 236 void *
 237 util_cache_get(struct util_cache *cache,
 238                const void *key)
 239 {
 240    struct util_cache_entry *entry;
 241    uint32_t hash;
 242
 243    assert(cache);
 244    if (!cache)
 245       return NULL;
 246    hash = cache->hash(key);
 247    entry = util_cache_entry_get(cache, hash, key);
 248    if (!entry)
 249       return NULL;
 250
 251    if (entry->state == FILLED)
 252       move_to_head(&cache->lru, entry);
 253
 254    return entry->value;
 255 }
 256
 257
 258 /**
 259  * Remove all entries from the cache.  The 'destroy' function will be called
 260  * for each entry's (key, value).
 261  */
 262 void
 263 util_cache_clear(struct util_cache *cache)
 264 {
 265    uint32_t i;
 266
 267    assert(cache);
 268    if (!cache)
 269       return;
 270
 271    for (i = 0; i < cache->size; ++i) {
 272       util_cache_entry_destroy(cache, &cache->entries[i]);
 273       cache->entries[i].state = EMPTY;
 274    }
 275
 276    assert(cache->count == 0);
 277    assert(is_empty_list(&cache->lru));
 278    ensure_sanity(cache);
 279 }
 280
 281
 282 /**
 283  * Destroy the cache and all entries.
 284  */
 285 void
 286 util_cache_destroy(struct util_cache *cache)
 287 {
 288    assert(cache);
 289    if (!cache)
 290       return;
 291
 292 #ifdef DEBUG
 293    if (cache->count >= 20*cache->size) {
 294       /* Normal approximation of the Poisson distribution */
 295       double mean = (double)cache->count/(double)cache->size;
 296       double stddev = sqrt(mean);
 297       unsigned i;
 298       for (i = 0; i < cache->size; ++i) {
 299          double z = fabs(cache->entries[i].count - mean)/stddev;
 300          /* This assert should not fail 99.9999998027% of the times, unless
 301           * the hash function is a poor one */
 302          assert(z <= 6.0);
 303       }
 304    }
 305 #endif
 306
 307    util_cache_clear(cache);
 308
 309    FREE(cache->entries);
 310    FREE(cache);
 311 }
 312
 313
 314 /**
 315  * Remove the cache entry which matches the given key.
 316  */
 317 void
 318 util_cache_remove(struct util_cache *cache,
 319                   const void *key)
 320 {
 321    struct util_cache_entry *entry;
 322    uint32_t hash;
 323
 324    assert(cache);
 325    if (!cache)
 326       return;
 327
 328    hash = cache->hash(key);
 329
 330    entry = util_cache_entry_get(cache, hash, key);
 331    if (!entry)
 332       return;
 333
 334    if (entry->state == FILLED)
 335       util_cache_entry_destroy(cache, entry);
 336
 337    ensure_sanity(cache);
 338 }
 339
 340
 341 static void
 342 ensure_sanity(const struct util_cache *cache)
 343 {
 344 #ifdef DEBUG
 345    unsigned i, cnt = 0;
 346
 347    assert(cache);
 348    for (i = 0; i < cache->size; i++) {
 349       struct util_cache_entry *header = &cache->entries[i];
 350
 351       assert(header);
 352       assert(header->state == FILLED ||
 353              header->state == EMPTY ||
 354              header->state == DELETED);
 355       if (header->state == FILLED) {
 356          cnt++;
 357          assert(header->hash == cache->hash(header->key));
 358       }
 359    }
 360
 361    assert(cnt == cache->count);
 362    assert(cache->size >= cnt);
 363
 364    if (cache->count == 0) {
 365       assert (is_empty_list(&cache->lru));
 366    }
 367    else {
 368       struct util_cache_entry *header = cache->lru.next;
 369
 370       assert (header);
 371       assert (!is_empty_list(&cache->lru));
 372
 373       for (i = 0; i < cache->count; i++)
 374          header = header->next;
 375
 376       assert(header == &cache->lru);
 377    }
 378 #endif
 379
 380    (void)cache;
 381 }