rculfhash.c

   1 /*
   2  * rculfhash.c
   3  *
   4  * Userspace RCU library - Lock-Free Expandable RCU Hash Table
   5  *
   6  * Copyright 2010-2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #define _LGPL_SOURCE
  24 #include <stdlib.h>
  25 #include <errno.h>
  26 #include <assert.h>
  27 #include <stdio.h>
  28 #include <stdint.h>
  29 #include <string.h>
  30
  31 #include <urcu.h>
  32 #include <urcu-call-rcu.h>
  33 #include <urcu/arch.h>
  34 #include <urcu/uatomic.h>
  35 #include <urcu/jhash.h>
  36 #include <urcu/compiler.h>
  37 #include <urcu/rculfhash.h>
  38 #include <stdio.h>
  39 #include <pthread.h>
  40
  41 #define DEBUG           /* Test */
  42
  43 #ifdef DEBUG
  44 #define dbg_printf(args...)     printf(args)
  45 #else
  46 #define dbg_printf(args...)
  47 #endif
  48
  49 #define BUCKET_SIZE_RESIZE_THRESHOLD    4
  50
  51 #ifndef max
  52 #define max(a, b)       ((a) > (b) ? (a) : (b))
  53 #endif
  54
  55 struct rcu_table {
  56         unsigned long size;     /* always a power of 2 */
  57         unsigned long resize_target;
  58         struct rcu_head head;
  59         struct rcu_ht_node *tbl[0];
  60 };
  61
  62 struct rcu_ht {
  63         struct rcu_table *t;            /* shared */
  64         ht_hash_fct hash_fct;
  65         ht_compare_fct compare_fct;
  66         unsigned long hash_seed;
  67         pthread_mutex_t resize_mutex;   /* resize mutex: add/del mutex */
  68         void (*ht_call_rcu)(struct rcu_head *head,
  69                       void (*func)(struct rcu_head *head));
  70 };
  71
  72 struct rcu_resize_work {
  73         struct rcu_head head;
  74         struct rcu_ht *ht;
  75 };
  76
  77 /*
  78  * Algorithm to reverse bits in a word by lookup table, extended to
  79  * 64-bit words.
  80  * Source:
  81  * http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
  82  * Originally from Public Domain.
  83  */
  84
  85 static const uint8_t BitReverseTable256[256] =
  86 {
  87 #define R2(n) (n),   (n) + 2*64,     (n) + 1*64,     (n) + 3*64
  88 #define R4(n) R2(n), R2((n) + 2*16), R2((n) + 1*16), R2((n) + 3*16)
  89 #define R6(n) R4(n), R4((n) + 2*4 ), R4((n) + 1*4 ), R4((n) + 3*4 )
  90         R6(0), R6(2), R6(1), R6(3)
  91 };
  92 #undef R2
  93 #undef R4
  94 #undef R6
  95
  96 static
  97 uint8_t bit_reverse_u8(uint8_t v)
  98 {
  99         return BitReverseTable256[v];
 100 }
 101
 102 static __attribute__((unused))
 103 uint32_t bit_reverse_u32(uint32_t v)
 104 {
 105         return ((uint32_t) bit_reverse_u8(v) << 24) |
 106                 ((uint32_t) bit_reverse_u8(v >> 8) << 16) |
 107                 ((uint32_t) bit_reverse_u8(v >> 16) << 8) |
 108                 ((uint32_t) bit_reverse_u8(v >> 24));
 109 }
 110
 111 static __attribute__((unused))
 112 uint64_t bit_reverse_u64(uint64_t v)
 113 {
 114         return ((uint64_t) bit_reverse_u8(v) << 56) |
 115                 ((uint64_t) bit_reverse_u8(v >> 8)  << 48) |
 116                 ((uint64_t) bit_reverse_u8(v >> 16) << 40) |
 117                 ((uint64_t) bit_reverse_u8(v >> 24) << 32) |
 118                 ((uint64_t) bit_reverse_u8(v >> 32) << 24) |
 119                 ((uint64_t) bit_reverse_u8(v >> 40) << 16) |
 120                 ((uint64_t) bit_reverse_u8(v >> 48) << 8) |
 121                 ((uint64_t) bit_reverse_u8(v >> 56));
 122 }
 123
 124 static
 125 unsigned long bit_reverse_ulong(unsigned long v)
 126 {
 127 #if (CAA_BITS_PER_LONG == 32)
 128         return bit_reverse_u32(v);
 129 #else
 130         return bit_reverse_u64(v);
 131 #endif
 132 }
 133
 134 /*
 135  * Algorithm to find the log2 of a 32-bit unsigned integer.
 136  * source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup
 137  * Originally from Public Domain.
 138  */
 139 static const char LogTable256[256] =
 140 {
 141 #define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n
 142         -1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
 143         LT(4), LT(5), LT(5), LT(6), LT(6), LT(6), LT(6),
 144         LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7)
 145 };
 146
 147 uint32_t log2_u32(uint32_t v)
 148 {
 149         uint32_t t, tt;
 150
 151         if ((tt = (v >> 16)))
 152                 return (t = (tt >> 8))
 153                                 ? 24 + LogTable256[t]
 154                                 : 16 + LogTable256[tt];
 155         else
 156                 return (t = (v >> 8))
 157                                 ? 8 + LogTable256[t]
 158                                 : LogTable256[v];
 159 }
 160
 161 static
 162 void ht_resize_lazy(struct rcu_ht *ht, struct rcu_table *t, int growth);
 163
 164 static
 165 void check_resize(struct rcu_ht *ht, struct rcu_table *t,
 166                   uint32_t chain_len)
 167 {
 168         if (chain_len >= BUCKET_SIZE_RESIZE_THRESHOLD)
 169                 ht_resize_lazy(ht, t, log2_u32(chain_len));
 170 }
 171
 172 static
 173 struct rcu_ht_node *clear_flag(struct rcu_ht_node *node)
 174 {
 175         return (struct rcu_ht_node *) (((unsigned long) node) & ~0x1);
 176 }
 177
 178 static
 179 int is_removed(struct rcu_ht_node *node)
 180 {
 181         return ((unsigned long) node) & 0x1;
 182 }
 183
 184 static
 185 struct rcu_ht_node *flag_removed(struct rcu_ht_node *node)
 186 {
 187         return (struct rcu_ht_node *) (((unsigned long) node) | 0x1);
 188 }
 189
 190 static
 191 unsigned long _uatomic_max(unsigned long *ptr, unsigned long v)
 192 {
 193         unsigned long old1, old2;
 194
 195         old1 = uatomic_read(ptr);
 196         do {
 197                 old2 = old1;
 198                 if (old2 >= v)
 199                         return old2;
 200         } while ((old1 = uatomic_cmpxchg(ptr, old2, v)) != old2);
 201         return v;
 202 }
 203
 204 static
 205 void _ht_add(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node)
 206 {
 207         struct rcu_ht_node *iter_prev = NULL, *iter = NULL;
 208
 209         if (!t->size)
 210                 return;
 211         for (;;) {
 212                 uint32_t chain_len = 0;
 213
 214                 iter_prev = rcu_dereference(t->tbl[node->hash & (t->size - 1)]);
 215                 assert(iter_prev);
 216                 assert(iter_prev->reverse_hash <= node->reverse_hash);
 217                 for (;;) {
 218                         iter = clear_flag(rcu_dereference(iter_prev->next));
 219                         if (unlikely(!iter))
 220                                 break;
 221                         if (iter->reverse_hash < node->reverse_hash)
 222                                 break;
 223                         iter_prev = iter;
 224                         check_resize(ht, t, ++chain_len);
 225                 }
 226                 /* add in iter_prev->next */
 227                 if (is_removed(iter))
 228                         continue;
 229                 assert(node != iter);
 230                 node->next = iter;
 231                 assert(iter_prev != node);
 232                 if (uatomic_cmpxchg(&iter_prev->next, iter, node) != iter)
 233                         continue;
 234                 break;
 235         }
 236 }
 237
 238 static
 239 int _ht_remove(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node)
 240 {
 241         struct rcu_ht_node *iter_prev, *iter, *next, *old;
 242         unsigned long chain_len;
 243         int found, ret = 0;
 244         int flagged = 0;
 245
 246 retry:
 247         chain_len = 0;
 248         found = 0;
 249         iter_prev = rcu_dereference(t->tbl[node->hash & (t->size - 1)]);
 250         assert(iter_prev);
 251         assert(iter_prev->reverse_hash <= node->reverse_hash);
 252         for (;;) {
 253                 iter = clear_flag(rcu_dereference(iter_prev->next));
 254                 if (unlikely(!iter))
 255                         break;
 256                 if (iter->reverse_hash < node->reverse_hash)
 257                         break;
 258                 if (iter == node) {
 259                         found = 1;
 260                         break;
 261                 }
 262                 iter_prev = iter;
 263         }
 264         if (!found) {
 265                 ret = -ENOENT;
 266                 goto end;
 267         }
 268         next = rcu_dereference(iter->next);
 269         if (!flagged) {
 270                 if (is_removed(next)) {
 271                         ret = -ENOENT;
 272                         goto end;
 273                 }
 274                 /* set deletion flag */
 275                 if ((old = uatomic_cmpxchg(&iter->next, next,
 276                                            flag_removed(next))) != next) {
 277                         if (old == flag_removed(next)) {
 278                                 ret = -ENOENT;
 279                                 goto end;
 280                         } else {
 281                                 goto retry;
 282                         }
 283                 }
 284                 flagged = 1;
 285         }
 286         /*
 287          * Remove the element from the list. Retry if there has been a
 288          * concurrent add (there cannot be a concurrent delete, because
 289          * we won the deletion flag cmpxchg).
 290          */
 291         if (uatomic_cmpxchg(&iter_prev->next, iter, clear_flag(next)) != iter)
 292                 goto retry;
 293 end:
 294         return ret;
 295 }
 296
 297 static
 298 void init_table(struct rcu_ht *ht, struct rcu_table *t,
 299                 unsigned long first, unsigned long len)
 300 {
 301         unsigned long i, end;
 302
 303         end = first + len;
 304         for (i = first; i < end; i++) {
 305                 /* Update table size when power of two */
 306                 if (i != 0 && !(i & (i - 1)))
 307                         t->size = i;
 308                 t->tbl[i] = calloc(1, sizeof(struct rcu_ht_node));
 309                 t->tbl[i]->dummy = 1;
 310                 t->tbl[i]->hash = i;
 311                 t->tbl[i]->reverse_hash = bit_reverse_ulong(i);
 312                 _ht_add(ht, t, t->tbl[i]);
 313         }
 314         t->resize_target = t->size = end;
 315 }
 316
 317 struct rcu_ht *ht_new(ht_hash_fct hash_fct,
 318                       ht_compare_fct compare_fct,
 319                       unsigned long hash_seed,
 320                       unsigned long init_size,
 321                       void (*ht_call_rcu)(struct rcu_head *head,
 322                                 void (*func)(struct rcu_head *head)))
 323 {
 324         struct rcu_ht *ht;
 325
 326         ht = calloc(1, sizeof(struct rcu_ht));
 327         ht->hash_fct = hash_fct;
 328         ht->compare_fct = compare_fct;
 329         ht->hash_seed = hash_seed;
 330         ht->ht_call_rcu = ht_call_rcu;
 331         /* this mutex should not nest in read-side C.S. */
 332         pthread_mutex_init(&ht->resize_mutex, NULL);
 333         ht->t = calloc(1, sizeof(struct rcu_table)
 334                        + (max(init_size, 1) * sizeof(struct rcu_ht_node *)));
 335         ht->t->size = 0;
 336         pthread_mutex_lock(&ht->resize_mutex);
 337         init_table(ht, ht->t, 0, max(init_size, 1));
 338         pthread_mutex_unlock(&ht->resize_mutex);
 339         return ht;
 340 }
 341
 342 struct rcu_ht_node *ht_lookup(struct rcu_ht *ht, void *key, size_t key_len)
 343 {
 344         struct rcu_table *t;
 345         struct rcu_ht_node *node;
 346         unsigned long hash, reverse_hash;
 347
 348         hash = ht->hash_fct(key, key_len, ht->hash_seed);
 349         reverse_hash = bit_reverse_ulong(hash);
 350
 351         t = rcu_dereference(ht->t);
 352         node = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 353         for (;;) {
 354                 if (unlikely(!node))
 355                         break;
 356                 if (node->reverse_hash > reverse_hash) {
 357                         node = NULL;
 358                         break;
 359                 }
 360                 if (!ht->compare_fct(node->key, node->key_len, key, key_len)) {
 361                         if (is_removed(rcu_dereference(node->next)))
 362                                 node = NULL;
 363                         break;
 364                 }
 365                 node = clear_flag(rcu_dereference(node->next));
 366         }
 367         return node;
 368 }
 369
 370 void ht_add(struct rcu_ht *ht, struct rcu_ht_node *node)
 371 {
 372         struct rcu_table *t;
 373
 374         node->hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
 375         node->reverse_hash = bit_reverse_ulong((unsigned long) node->hash);
 376
 377         t = rcu_dereference(ht->t);
 378         _ht_add(ht, t, node);
 379 }
 380
 381 int ht_remove(struct rcu_ht *ht, struct rcu_ht_node *node)
 382 {
 383         struct rcu_table *t;
 384
 385         t = rcu_dereference(ht->t);
 386         return _ht_remove(ht, t, node);
 387 }
 388
 389 static
 390 int ht_delete_dummy(struct rcu_ht *ht)
 391 {
 392         struct rcu_table *t;
 393         struct rcu_ht_node *node;
 394         unsigned long i;
 395
 396         t = ht->t;
 397         /* Check that the table is empty */
 398         node = t->tbl[0];
 399         do {
 400                 if (!node->dummy)
 401                         return -EPERM;
 402                 node = node->next;
 403         } while (node);
 404         /* Internal sanity check: all nodes left should be dummy */
 405         for (i = 0; i < t->size; i++) {
 406                 assert(t->tbl[i]->dummy);
 407                 free(t->tbl[i]);
 408         }
 409         return 0;
 410 }
 411
 412 /*
 413  * Should only be called when no more concurrent readers nor writers can
 414  * possibly access the table.
 415  */
 416 int ht_destroy(struct rcu_ht *ht)
 417 {
 418         int ret;
 419
 420         ret = ht_delete_dummy(ht);
 421         if (ret)
 422                 return ret;
 423         free(ht->t);
 424         free(ht);
 425         return ret;
 426 }
 427
 428 static
 429 void ht_free_table_cb(struct rcu_head *head)
 430 {
 431         struct rcu_table *t =
 432                 caa_container_of(head, struct rcu_table, head);
 433         free(t);
 434 }
 435
 436 /* called with resize mutex held */
 437 static
 438 void _do_ht_resize(struct rcu_ht *ht)
 439 {
 440         unsigned long new_size, old_size;
 441         struct rcu_table *new_t, *old_t;
 442
 443         old_t = ht->t;
 444         old_size = old_t->size;
 445
 446         new_size = CMM_LOAD_SHARED(old_t->resize_target);
 447         dbg_printf("rculfhash: resize from %lu to %lu buckets\n",
 448                    old_size, new_size);
 449         if (old_size == new_size)
 450                 return;
 451         new_t = malloc(sizeof(struct rcu_table)
 452                         + (new_size * sizeof(struct rcu_ht_node *)));
 453         assert(new_size > old_size);
 454         memcpy(&new_t->tbl, &old_t->tbl,
 455                old_size * sizeof(struct rcu_ht_node *));
 456         init_table(ht, new_t, old_size, new_size - old_size);
 457         /* Changing table and size atomically wrt lookups */
 458         rcu_assign_pointer(ht->t, new_t);
 459         ht->ht_call_rcu(&old_t->head, ht_free_table_cb);
 460 }
 461
 462 static
 463 unsigned long resize_target_update(struct rcu_table *t,
 464                                    int growth_order)
 465 {
 466         return _uatomic_max(&t->resize_target,
 467                             t->size << growth_order);
 468 }
 469
 470 void ht_resize(struct rcu_ht *ht, int growth)
 471 {
 472         struct rcu_table *t = rcu_dereference(ht->t);
 473         unsigned long target_size;
 474
 475         target_size = resize_target_update(t, growth);
 476         if (t->size < target_size) {
 477                 pthread_mutex_lock(&ht->resize_mutex);
 478                 _do_ht_resize(ht);
 479                 pthread_mutex_unlock(&ht->resize_mutex);
 480         }
 481 }
 482
 483 static
 484 void do_resize_cb(struct rcu_head *head)
 485 {
 486         struct rcu_resize_work *work =
 487                 caa_container_of(head, struct rcu_resize_work, head);
 488         struct rcu_ht *ht = work->ht;
 489
 490         pthread_mutex_lock(&ht->resize_mutex);
 491         _do_ht_resize(ht);
 492         pthread_mutex_unlock(&ht->resize_mutex);
 493         free(work);
 494 }
 495
 496 static
 497 void ht_resize_lazy(struct rcu_ht *ht, struct rcu_table *t, int growth)
 498 {
 499         struct rcu_resize_work *work;
 500         unsigned long target_size;
 501
 502         target_size = resize_target_update(t, growth);
 503         if (t->size < target_size) {
 504                 work = malloc(sizeof(*work));
 505                 work->ht = ht;
 506                 ht->ht_call_rcu(&work->head, do_resize_cb);
 507         }
 508 }