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 CHAIN_LEN_TARGET                1
  50 #define CHAIN_LEN_RESIZE_THRESHOLD      2
  51
  52 #ifndef max
  53 #define max(a, b)       ((a) > (b) ? (a) : (b))
  54 #endif
  55
  56 struct rcu_table {
  57         unsigned long size;     /* always a power of 2 */
  58         unsigned long resize_target;
  59         int resize_initiated;
  60         struct rcu_head head;
  61         struct rcu_ht_node *tbl[0];
  62 };
  63
  64 struct rcu_ht {
  65         struct rcu_table *t;            /* shared */
  66         ht_hash_fct hash_fct;
  67         ht_compare_fct compare_fct;
  68         unsigned long hash_seed;
  69         pthread_mutex_t resize_mutex;   /* resize mutex: add/del mutex */
  70         void (*ht_call_rcu)(struct rcu_head *head,
  71                       void (*func)(struct rcu_head *head));
  72 };
  73
  74 struct rcu_resize_work {
  75         struct rcu_head head;
  76         struct rcu_ht *ht;
  77 };
  78
  79 /*
  80  * Algorithm to reverse bits in a word by lookup table, extended to
  81  * 64-bit words.
  82  * Source:
  83  * http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
  84  * Originally from Public Domain.
  85  */
  86
  87 static const uint8_t BitReverseTable256[256] =
  88 {
  89 #define R2(n) (n),   (n) + 2*64,     (n) + 1*64,     (n) + 3*64
  90 #define R4(n) R2(n), R2((n) + 2*16), R2((n) + 1*16), R2((n) + 3*16)
  91 #define R6(n) R4(n), R4((n) + 2*4 ), R4((n) + 1*4 ), R4((n) + 3*4 )
  92         R6(0), R6(2), R6(1), R6(3)
  93 };
  94 #undef R2
  95 #undef R4
  96 #undef R6
  97
  98 static
  99 uint8_t bit_reverse_u8(uint8_t v)
 100 {
 101         return BitReverseTable256[v];
 102 }
 103
 104 static __attribute__((unused))
 105 uint32_t bit_reverse_u32(uint32_t v)
 106 {
 107         return ((uint32_t) bit_reverse_u8(v) << 24) |
 108                 ((uint32_t) bit_reverse_u8(v >> 8) << 16) |
 109                 ((uint32_t) bit_reverse_u8(v >> 16) << 8) |
 110                 ((uint32_t) bit_reverse_u8(v >> 24));
 111 }
 112
 113 static __attribute__((unused))
 114 uint64_t bit_reverse_u64(uint64_t v)
 115 {
 116         return ((uint64_t) bit_reverse_u8(v) << 56) |
 117                 ((uint64_t) bit_reverse_u8(v >> 8)  << 48) |
 118                 ((uint64_t) bit_reverse_u8(v >> 16) << 40) |
 119                 ((uint64_t) bit_reverse_u8(v >> 24) << 32) |
 120                 ((uint64_t) bit_reverse_u8(v >> 32) << 24) |
 121                 ((uint64_t) bit_reverse_u8(v >> 40) << 16) |
 122                 ((uint64_t) bit_reverse_u8(v >> 48) << 8) |
 123                 ((uint64_t) bit_reverse_u8(v >> 56));
 124 }
 125
 126 static
 127 unsigned long bit_reverse_ulong(unsigned long v)
 128 {
 129 #if (CAA_BITS_PER_LONG == 32)
 130         return bit_reverse_u32(v);
 131 #else
 132         return bit_reverse_u64(v);
 133 #endif
 134 }
 135
 136 /*
 137  * Algorithm to find the log2 of a 32-bit unsigned integer.
 138  * source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup
 139  * Originally from Public Domain.
 140  */
 141 static const char LogTable256[256] =
 142 {
 143 #define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n
 144         -1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
 145         LT(4), LT(5), LT(5), LT(6), LT(6), LT(6), LT(6),
 146         LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7)
 147 };
 148
 149 uint32_t log2_u32(uint32_t v)
 150 {
 151         uint32_t t, tt;
 152
 153         if ((tt = (v >> 16)))
 154                 return (t = (tt >> 8))
 155                                 ? 24 + LogTable256[t]
 156                                 : 16 + LogTable256[tt];
 157         else
 158                 return (t = (v >> 8))
 159                                 ? 8 + LogTable256[t]
 160                                 : LogTable256[v];
 161 }
 162
 163 static
 164 void ht_resize_lazy(struct rcu_ht *ht, struct rcu_table *t, int growth);
 165
 166 static
 167 void check_resize(struct rcu_ht *ht, struct rcu_table *t,
 168                   uint32_t chain_len)
 169 {
 170         if (chain_len >= CHAIN_LEN_RESIZE_THRESHOLD)
 171                 ht_resize_lazy(ht, t,
 172                         log2_u32(chain_len - CHAIN_LEN_TARGET - 1));
 173 }
 174
 175 static
 176 struct rcu_ht_node *clear_flag(struct rcu_ht_node *node)
 177 {
 178         return (struct rcu_ht_node *) (((unsigned long) node) & ~0x1);
 179 }
 180
 181 static
 182 int is_removed(struct rcu_ht_node *node)
 183 {
 184         return ((unsigned long) node) & 0x1;
 185 }
 186
 187 static
 188 struct rcu_ht_node *flag_removed(struct rcu_ht_node *node)
 189 {
 190         return (struct rcu_ht_node *) (((unsigned long) node) | 0x1);
 191 }
 192
 193 static
 194 unsigned long _uatomic_max(unsigned long *ptr, unsigned long v)
 195 {
 196         unsigned long old1, old2;
 197
 198         old1 = uatomic_read(ptr);
 199         do {
 200                 old2 = old1;
 201                 if (old2 >= v)
 202                         return old2;
 203         } while ((old1 = uatomic_cmpxchg(ptr, old2, v)) != old2);
 204         return v;
 205 }
 206
 207 /*
 208  * Remove all logically deleted nodes from a bucket up to a certain node key.
 209  */
 210 static
 211 void _ht_gc_bucket(struct rcu_ht_node *dummy, struct rcu_ht_node *node)
 212 {
 213         struct rcu_ht_node *iter_prev, *iter, *next;
 214
 215         for (;;) {
 216                 iter_prev = dummy;
 217                 /* We can always skip the dummy node initially */
 218                 iter = rcu_dereference(iter_prev->next);
 219                 assert(iter_prev->reverse_hash <= node->reverse_hash);
 220                 for (;;) {
 221                         if (unlikely(!iter))
 222                                 return;
 223                         if (clear_flag(iter)->reverse_hash > node->reverse_hash)
 224                                 return;
 225                         next = rcu_dereference(clear_flag(iter)->next);
 226                         if (is_removed(next))
 227                                 break;
 228                         iter_prev = iter;
 229                         iter = next;
 230                 }
 231                 assert(!is_removed(iter));
 232                 (void) uatomic_cmpxchg(&iter_prev->next, iter, clear_flag(next));
 233         }
 234 }
 235
 236 static
 237 int _ht_add(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node,
 238              int unique)
 239 {
 240         struct rcu_ht_node *iter_prev, *dummy, *iter, *next;
 241         unsigned long hash;
 242
 243         if (!t->size)
 244                 return 0;
 245         hash = bit_reverse_ulong(node->reverse_hash);
 246         for (;;) {
 247                 uint32_t chain_len = 0;
 248
 249                 /*
 250                  * iter_prev points to the non-removed node prior to the
 251                  * insert location.
 252                  */
 253                 iter_prev = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 254                 /* We can always skip the dummy node initially */
 255                 iter = rcu_dereference(iter_prev->next);
 256                 assert(iter_prev->reverse_hash <= node->reverse_hash);
 257                 for (;;) {
 258                         if (unlikely(!iter))
 259                                 goto insert;
 260                         if (clear_flag(iter)->reverse_hash > node->reverse_hash)
 261                                 goto insert;
 262                         next = rcu_dereference(clear_flag(iter)->next);
 263                         if (is_removed(next))
 264                                 goto gc_node;
 265                         /* Only account for identical reverse hash once */
 266                         if (iter_prev->reverse_hash != clear_flag(iter)->reverse_hash)
 267                                 check_resize(ht, t, ++chain_len);
 268                         iter_prev = clear_flag(iter);
 269                         iter = next;
 270                 }
 271         insert:
 272                 assert(node != clear_flag(iter));
 273                 assert(!is_removed(iter_prev));
 274                 assert(iter_prev != node);
 275                 node->next = iter;
 276                 if (uatomic_cmpxchg(&iter_prev->next, iter,
 277                                     node) != iter)
 278                         continue;       /* retry */
 279                 else
 280                         goto gc_end;
 281         gc_node:
 282                 assert(!is_removed(iter));
 283                 (void) uatomic_cmpxchg(&iter_prev->next, iter, clear_flag(next));
 284                 /* retry */
 285         }
 286 gc_end:
 287         /* Garbage collect logically removed nodes in the bucket */
 288         dummy = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 289         _ht_gc_bucket(dummy, node);
 290         return 0;
 291 }
 292
 293 static
 294 int _ht_remove(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node)
 295 {
 296         struct rcu_ht_node *dummy, *next, *old;
 297         int flagged = 0;
 298         unsigned long hash;
 299
 300         /* logically delete the node */
 301         old = rcu_dereference(node->next);
 302         do {
 303                 next = old;
 304                 if (is_removed(next))
 305                         goto end;
 306                 assert(!node->dummy);
 307                 old = uatomic_cmpxchg(&node->next, next,
 308                                       flag_removed(next));
 309         } while (old != next);
 310
 311         /* We performed the (logical) deletion. */
 312         flagged = 1;
 313
 314         /*
 315          * Ensure that the node is not visible to readers anymore: lookup for
 316          * the node, and remove it (along with any other logically removed node)
 317          * if found.
 318          */
 319         hash = bit_reverse_ulong(node->reverse_hash);
 320         dummy = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 321         _ht_gc_bucket(dummy, node);
 322 end:
 323         /*
 324          * Only the flagging action indicated that we (and no other)
 325          * removed the node from the hash.
 326          */
 327         if (flagged) {
 328                 assert(is_removed(rcu_dereference(node->next)));
 329                 return 0;
 330         } else
 331                 return -ENOENT;
 332 }
 333
 334 static
 335 void init_table(struct rcu_ht *ht, struct rcu_table *t,
 336                 unsigned long first, unsigned long len)
 337 {
 338         unsigned long i, end;
 339
 340         end = first + len;
 341         for (i = first; i < end; i++) {
 342                 /* Update table size when power of two */
 343                 if (i != 0 && !(i & (i - 1)))
 344                         t->size = i;
 345                 t->tbl[i] = calloc(1, sizeof(struct rcu_ht_node));
 346                 t->tbl[i]->dummy = 1;
 347                 t->tbl[i]->reverse_hash = bit_reverse_ulong(i);
 348                 (void) _ht_add(ht, t, t->tbl[i], 0);
 349         }
 350         t->resize_target = t->size = end;
 351         t->resize_initiated = 0;
 352 }
 353
 354 struct rcu_ht *ht_new(ht_hash_fct hash_fct,
 355                       ht_compare_fct compare_fct,
 356                       unsigned long hash_seed,
 357                       unsigned long init_size,
 358                       void (*ht_call_rcu)(struct rcu_head *head,
 359                                 void (*func)(struct rcu_head *head)))
 360 {
 361         struct rcu_ht *ht;
 362
 363         ht = calloc(1, sizeof(struct rcu_ht));
 364         ht->hash_fct = hash_fct;
 365         ht->compare_fct = compare_fct;
 366         ht->hash_seed = hash_seed;
 367         ht->ht_call_rcu = ht_call_rcu;
 368         /* this mutex should not nest in read-side C.S. */
 369         pthread_mutex_init(&ht->resize_mutex, NULL);
 370         ht->t = calloc(1, sizeof(struct rcu_table)
 371                        + (max(init_size, 1) * sizeof(struct rcu_ht_node *)));
 372         ht->t->size = 0;
 373         pthread_mutex_lock(&ht->resize_mutex);
 374         init_table(ht, ht->t, 0, max(init_size, 1));
 375         pthread_mutex_unlock(&ht->resize_mutex);
 376         return ht;
 377 }
 378
 379 struct rcu_ht_node *ht_lookup(struct rcu_ht *ht, void *key, size_t key_len)
 380 {
 381         struct rcu_table *t;
 382         struct rcu_ht_node *node;
 383         unsigned long hash, reverse_hash;
 384
 385         hash = ht->hash_fct(key, key_len, ht->hash_seed);
 386         reverse_hash = bit_reverse_ulong(hash);
 387
 388         t = rcu_dereference(ht->t);
 389         node = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 390         for (;;) {
 391                 if (unlikely(!node))
 392                         break;
 393                 if (unlikely(node->reverse_hash > reverse_hash)) {
 394                         node = NULL;
 395                         break;
 396                 }
 397                 if (likely(!is_removed(rcu_dereference(node->next)))
 398                     && !node->dummy
 399                     && likely(!ht->compare_fct(node->key, node->key_len, key, key_len))) {
 400                                 break;
 401                 }
 402                 node = clear_flag(rcu_dereference(node->next));
 403         }
 404         assert(!node || !node->dummy);
 405         return node;
 406 }
 407
 408 void ht_add(struct rcu_ht *ht, struct rcu_ht_node *node)
 409 {
 410         struct rcu_table *t;
 411         unsigned long hash;
 412
 413         hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
 414         node->reverse_hash = bit_reverse_ulong((unsigned long) hash);
 415
 416         t = rcu_dereference(ht->t);
 417         (void) _ht_add(ht, t, node, 0);
 418 }
 419
 420 int ht_add_unique(struct rcu_ht *ht, struct rcu_ht_node *node)
 421 {
 422         struct rcu_table *t;
 423         unsigned long hash;
 424
 425         hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
 426         node->reverse_hash = bit_reverse_ulong((unsigned long) hash);
 427
 428         t = rcu_dereference(ht->t);
 429         return _ht_add(ht, t, node, 1);
 430 }
 431
 432 int ht_remove(struct rcu_ht *ht, struct rcu_ht_node *node)
 433 {
 434         struct rcu_table *t;
 435
 436         t = rcu_dereference(ht->t);
 437         return _ht_remove(ht, t, node);
 438 }
 439
 440 static
 441 int ht_delete_dummy(struct rcu_ht *ht)
 442 {
 443         struct rcu_table *t;
 444         struct rcu_ht_node *node;
 445         unsigned long i;
 446
 447         t = ht->t;
 448         /* Check that the table is empty */
 449         node = t->tbl[0];
 450         do {
 451                 if (!node->dummy)
 452                         return -EPERM;
 453                 node = node->next;
 454                 assert(!is_removed(node));
 455         } while (node);
 456         /* Internal sanity check: all nodes left should be dummy */
 457         for (i = 0; i < t->size; i++) {
 458                 assert(t->tbl[i]->dummy);
 459                 free(t->tbl[i]);
 460         }
 461         return 0;
 462 }
 463
 464 /*
 465  * Should only be called when no more concurrent readers nor writers can
 466  * possibly access the table.
 467  */
 468 int ht_destroy(struct rcu_ht *ht)
 469 {
 470         int ret;
 471
 472         ret = ht_delete_dummy(ht);
 473         if (ret)
 474                 return ret;
 475         free(ht->t);
 476         free(ht);
 477         return ret;
 478 }
 479
 480 void ht_count_nodes(struct rcu_ht *ht,
 481                 unsigned long *count,
 482                 unsigned long *removed)
 483 {
 484         struct rcu_table *t;
 485         struct rcu_ht_node *node, *next;
 486
 487         *count = 0;
 488         *removed = 0;
 489
 490         t = rcu_dereference(ht->t);
 491         /* Check that the table is empty */
 492         node = rcu_dereference(t->tbl[0]);
 493         do {
 494                 next = rcu_dereference(node->next);
 495                 if (is_removed(next)) {
 496                         assert(!node->dummy);
 497                         (*removed)++;
 498                 } else if (!node->dummy)
 499                         (*count)++;
 500                 node = clear_flag(next);
 501         } while (node);
 502 }
 503
 504 static
 505 void ht_free_table_cb(struct rcu_head *head)
 506 {
 507         struct rcu_table *t =
 508                 caa_container_of(head, struct rcu_table, head);
 509         free(t);
 510 }
 511
 512 /* called with resize mutex held */
 513 static
 514 void _do_ht_resize(struct rcu_ht *ht)
 515 {
 516         unsigned long new_size, old_size;
 517         struct rcu_table *new_t, *old_t;
 518
 519         old_t = ht->t;
 520         old_size = old_t->size;
 521
 522         new_size = CMM_LOAD_SHARED(old_t->resize_target);
 523         dbg_printf("rculfhash: resize from %lu to %lu buckets\n",
 524                    old_size, new_size);
 525         if (old_size == new_size)
 526                 return;
 527         new_t = malloc(sizeof(struct rcu_table)
 528                         + (new_size * sizeof(struct rcu_ht_node *)));
 529         assert(new_size > old_size);
 530         memcpy(&new_t->tbl, &old_t->tbl,
 531                old_size * sizeof(struct rcu_ht_node *));
 532         init_table(ht, new_t, old_size, new_size - old_size);
 533         /* Changing table and size atomically wrt lookups */
 534         rcu_assign_pointer(ht->t, new_t);
 535         ht->ht_call_rcu(&old_t->head, ht_free_table_cb);
 536 }
 537
 538 static
 539 unsigned long resize_target_update(struct rcu_table *t,
 540                                    int growth_order)
 541 {
 542         return _uatomic_max(&t->resize_target,
 543                             t->size << growth_order);
 544 }
 545
 546 void ht_resize(struct rcu_ht *ht, int growth)
 547 {
 548         struct rcu_table *t = rcu_dereference(ht->t);
 549         unsigned long target_size;
 550
 551         target_size = resize_target_update(t, growth);
 552         if (t->size < target_size) {
 553                 CMM_STORE_SHARED(t->resize_initiated, 1);
 554                 pthread_mutex_lock(&ht->resize_mutex);
 555                 _do_ht_resize(ht);
 556                 pthread_mutex_unlock(&ht->resize_mutex);
 557         }
 558 }
 559
 560 static
 561 void do_resize_cb(struct rcu_head *head)
 562 {
 563         struct rcu_resize_work *work =
 564                 caa_container_of(head, struct rcu_resize_work, head);
 565         struct rcu_ht *ht = work->ht;
 566
 567         pthread_mutex_lock(&ht->resize_mutex);
 568         _do_ht_resize(ht);
 569         pthread_mutex_unlock(&ht->resize_mutex);
 570         free(work);
 571 }
 572
 573 static
 574 void ht_resize_lazy(struct rcu_ht *ht, struct rcu_table *t, int growth)
 575 {
 576         struct rcu_resize_work *work;
 577         unsigned long target_size;
 578
 579         target_size = resize_target_update(t, growth);
 580         if (!CMM_LOAD_SHARED(t->resize_initiated) && t->size < target_size) {
 581                 work = malloc(sizeof(*work));
 582                 work->ht = ht;
 583                 ht->ht_call_rcu(&work->head, do_resize_cb);
 584                 CMM_STORE_SHARED(t->resize_initiated, 1);
 585         }
 586 }