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 struct rcu_ht_node *_ht_add(struct rcu_ht *ht, struct rcu_table *t,
 238                             struct rcu_ht_node *node, int unique)
 239 {
 240         struct rcu_ht_node *iter_prev, *dummy, *iter, *next;
 241         unsigned long hash;
 242
 243         if (!t->size) {
 244                 assert(node->dummy);
 245                 return node;    /* Initial first add (head) */
 246         }
 247         hash = bit_reverse_ulong(node->reverse_hash);
 248         for (;;) {
 249                 uint32_t chain_len = 0;
 250
 251                 /*
 252                  * iter_prev points to the non-removed node prior to the
 253                  * insert location.
 254                  */
 255                 iter_prev = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 256                 /* We can always skip the dummy node initially */
 257                 iter = rcu_dereference(iter_prev->next);
 258                 assert(iter_prev->reverse_hash <= node->reverse_hash);
 259                 for (;;) {
 260                         if (unlikely(!iter))
 261                                 goto insert;
 262                         if (clear_flag(iter)->reverse_hash > node->reverse_hash)
 263                                 goto insert;
 264                         next = rcu_dereference(clear_flag(iter)->next);
 265                         if (is_removed(next))
 266                                 goto gc_node;
 267                         if (unique
 268                             && !clear_flag(iter)->dummy
 269                             && !ht->compare_fct(node->key, node->key_len,
 270                                                 clear_flag(iter)->key,
 271                                                 clear_flag(iter)->key_len))
 272                                 return clear_flag(iter);
 273                         /* Only account for identical reverse hash once */
 274                         if (iter_prev->reverse_hash != clear_flag(iter)->reverse_hash)
 275                                 check_resize(ht, t, ++chain_len);
 276                         iter_prev = clear_flag(iter);
 277                         iter = next;
 278                 }
 279         insert:
 280                 assert(node != clear_flag(iter));
 281                 assert(!is_removed(iter_prev));
 282                 assert(iter_prev != node);
 283                 node->next = iter;
 284                 if (uatomic_cmpxchg(&iter_prev->next, iter,
 285                                     node) != iter)
 286                         continue;       /* retry */
 287                 else
 288                         goto gc_end;
 289         gc_node:
 290                 assert(!is_removed(iter));
 291                 (void) uatomic_cmpxchg(&iter_prev->next, iter, clear_flag(next));
 292                 /* retry */
 293         }
 294 gc_end:
 295         /* Garbage collect logically removed nodes in the bucket */
 296         dummy = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 297         _ht_gc_bucket(dummy, node);
 298         return node;
 299 }
 300
 301 static
 302 int _ht_remove(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node)
 303 {
 304         struct rcu_ht_node *dummy, *next, *old;
 305         int flagged = 0;
 306         unsigned long hash;
 307
 308         /* logically delete the node */
 309         old = rcu_dereference(node->next);
 310         do {
 311                 next = old;
 312                 if (is_removed(next))
 313                         goto end;
 314                 assert(!node->dummy);
 315                 old = uatomic_cmpxchg(&node->next, next,
 316                                       flag_removed(next));
 317         } while (old != next);
 318
 319         /* We performed the (logical) deletion. */
 320         flagged = 1;
 321
 322         /*
 323          * Ensure that the node is not visible to readers anymore: lookup for
 324          * the node, and remove it (along with any other logically removed node)
 325          * if found.
 326          */
 327         hash = bit_reverse_ulong(node->reverse_hash);
 328         dummy = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 329         _ht_gc_bucket(dummy, node);
 330 end:
 331         /*
 332          * Only the flagging action indicated that we (and no other)
 333          * removed the node from the hash.
 334          */
 335         if (flagged) {
 336                 assert(is_removed(rcu_dereference(node->next)));
 337                 return 0;
 338         } else
 339                 return -ENOENT;
 340 }
 341
 342 static
 343 void init_table(struct rcu_ht *ht, struct rcu_table *t,
 344                 unsigned long first, unsigned long len)
 345 {
 346         unsigned long i, end;
 347
 348         end = first + len;
 349         for (i = first; i < end; i++) {
 350                 /* Update table size when power of two */
 351                 if (i != 0 && !(i & (i - 1)))
 352                         t->size = i;
 353                 t->tbl[i] = calloc(1, sizeof(struct rcu_ht_node));
 354                 t->tbl[i]->dummy = 1;
 355                 t->tbl[i]->reverse_hash = bit_reverse_ulong(i);
 356                 (void) _ht_add(ht, t, t->tbl[i], 0);
 357         }
 358         t->resize_target = t->size = end;
 359         t->resize_initiated = 0;
 360 }
 361
 362 struct rcu_ht *ht_new(ht_hash_fct hash_fct,
 363                       ht_compare_fct compare_fct,
 364                       unsigned long hash_seed,
 365                       unsigned long init_size,
 366                       void (*ht_call_rcu)(struct rcu_head *head,
 367                                 void (*func)(struct rcu_head *head)))
 368 {
 369         struct rcu_ht *ht;
 370
 371         ht = calloc(1, sizeof(struct rcu_ht));
 372         ht->hash_fct = hash_fct;
 373         ht->compare_fct = compare_fct;
 374         ht->hash_seed = hash_seed;
 375         ht->ht_call_rcu = ht_call_rcu;
 376         /* this mutex should not nest in read-side C.S. */
 377         pthread_mutex_init(&ht->resize_mutex, NULL);
 378         ht->t = calloc(1, sizeof(struct rcu_table)
 379                        + (max(init_size, 1) * sizeof(struct rcu_ht_node *)));
 380         ht->t->size = 0;
 381         pthread_mutex_lock(&ht->resize_mutex);
 382         init_table(ht, ht->t, 0, max(init_size, 1));
 383         pthread_mutex_unlock(&ht->resize_mutex);
 384         return ht;
 385 }
 386
 387 struct rcu_ht_node *ht_lookup(struct rcu_ht *ht, void *key, size_t key_len)
 388 {
 389         struct rcu_table *t;
 390         struct rcu_ht_node *node;
 391         unsigned long hash, reverse_hash;
 392
 393         hash = ht->hash_fct(key, key_len, ht->hash_seed);
 394         reverse_hash = bit_reverse_ulong(hash);
 395
 396         t = rcu_dereference(ht->t);
 397         node = rcu_dereference(t->tbl[hash & (t->size - 1)]);
 398         for (;;) {
 399                 if (unlikely(!node))
 400                         break;
 401                 if (unlikely(node->reverse_hash > reverse_hash)) {
 402                         node = NULL;
 403                         break;
 404                 }
 405                 if (likely(!is_removed(rcu_dereference(node->next)))
 406                     && !node->dummy
 407                     && likely(!ht->compare_fct(node->key, node->key_len, key, key_len))) {
 408                                 break;
 409                 }
 410                 node = clear_flag(rcu_dereference(node->next));
 411         }
 412         assert(!node || !node->dummy);
 413         return node;
 414 }
 415
 416 void ht_add(struct rcu_ht *ht, struct rcu_ht_node *node)
 417 {
 418         struct rcu_table *t;
 419         unsigned long hash;
 420
 421         hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
 422         node->reverse_hash = bit_reverse_ulong((unsigned long) hash);
 423
 424         t = rcu_dereference(ht->t);
 425         (void) _ht_add(ht, t, node, 0);
 426 }
 427
 428 struct rcu_ht_node *ht_add_unique(struct rcu_ht *ht, struct rcu_ht_node *node)
 429 {
 430         struct rcu_table *t;
 431         unsigned long hash;
 432
 433         hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
 434         node->reverse_hash = bit_reverse_ulong((unsigned long) hash);
 435
 436         t = rcu_dereference(ht->t);
 437         return _ht_add(ht, t, node, 1);
 438 }
 439
 440 int ht_remove(struct rcu_ht *ht, struct rcu_ht_node *node)
 441 {
 442         struct rcu_table *t;
 443
 444         t = rcu_dereference(ht->t);
 445         return _ht_remove(ht, t, node);
 446 }
 447
 448 static
 449 int ht_delete_dummy(struct rcu_ht *ht)
 450 {
 451         struct rcu_table *t;
 452         struct rcu_ht_node *node;
 453         unsigned long i;
 454
 455         t = ht->t;
 456         /* Check that the table is empty */
 457         node = t->tbl[0];
 458         do {
 459                 if (!node->dummy)
 460                         return -EPERM;
 461                 node = node->next;
 462                 assert(!is_removed(node));
 463         } while (node);
 464         /* Internal sanity check: all nodes left should be dummy */
 465         for (i = 0; i < t->size; i++) {
 466                 assert(t->tbl[i]->dummy);
 467                 free(t->tbl[i]);
 468         }
 469         return 0;
 470 }
 471
 472 /*
 473  * Should only be called when no more concurrent readers nor writers can
 474  * possibly access the table.
 475  */
 476 int ht_destroy(struct rcu_ht *ht)
 477 {
 478         int ret;
 479
 480         ret = ht_delete_dummy(ht);
 481         if (ret)
 482                 return ret;
 483         free(ht->t);
 484         free(ht);
 485         return ret;
 486 }
 487
 488 void ht_count_nodes(struct rcu_ht *ht,
 489                 unsigned long *count,
 490                 unsigned long *removed)
 491 {
 492         struct rcu_table *t;
 493         struct rcu_ht_node *node, *next;
 494
 495         *count = 0;
 496         *removed = 0;
 497
 498         t = rcu_dereference(ht->t);
 499         /* Check that the table is empty */
 500         node = rcu_dereference(t->tbl[0]);
 501         do {
 502                 next = rcu_dereference(node->next);
 503                 if (is_removed(next)) {
 504                         assert(!node->dummy);
 505                         (*removed)++;
 506                 } else if (!node->dummy)
 507                         (*count)++;
 508                 node = clear_flag(next);
 509         } while (node);
 510 }
 511
 512 static
 513 void ht_free_table_cb(struct rcu_head *head)
 514 {
 515         struct rcu_table *t =
 516                 caa_container_of(head, struct rcu_table, head);
 517         free(t);
 518 }
 519
 520 /* called with resize mutex held */
 521 static
 522 void _do_ht_resize(struct rcu_ht *ht)
 523 {
 524         unsigned long new_size, old_size;
 525         struct rcu_table *new_t, *old_t;
 526
 527         old_t = ht->t;
 528         old_size = old_t->size;
 529
 530         new_size = CMM_LOAD_SHARED(old_t->resize_target);
 531         dbg_printf("rculfhash: resize from %lu to %lu buckets\n",
 532                    old_size, new_size);
 533         if (old_size == new_size)
 534                 return;
 535         new_t = malloc(sizeof(struct rcu_table)
 536                         + (new_size * sizeof(struct rcu_ht_node *)));
 537         assert(new_size > old_size);
 538         memcpy(&new_t->tbl, &old_t->tbl,
 539                old_size * sizeof(struct rcu_ht_node *));
 540         init_table(ht, new_t, old_size, new_size - old_size);
 541         /* Changing table and size atomically wrt lookups */
 542         rcu_assign_pointer(ht->t, new_t);
 543         ht->ht_call_rcu(&old_t->head, ht_free_table_cb);
 544 }
 545
 546 static
 547 unsigned long resize_target_update(struct rcu_table *t,
 548                                    int growth_order)
 549 {
 550         return _uatomic_max(&t->resize_target,
 551                             t->size << growth_order);
 552 }
 553
 554 void ht_resize(struct rcu_ht *ht, int growth)
 555 {
 556         struct rcu_table *t = rcu_dereference(ht->t);
 557         unsigned long target_size;
 558
 559         target_size = resize_target_update(t, growth);
 560         if (t->size < target_size) {
 561                 CMM_STORE_SHARED(t->resize_initiated, 1);
 562                 pthread_mutex_lock(&ht->resize_mutex);
 563                 _do_ht_resize(ht);
 564                 pthread_mutex_unlock(&ht->resize_mutex);
 565         }
 566 }
 567
 568 static
 569 void do_resize_cb(struct rcu_head *head)
 570 {
 571         struct rcu_resize_work *work =
 572                 caa_container_of(head, struct rcu_resize_work, head);
 573         struct rcu_ht *ht = work->ht;
 574
 575         pthread_mutex_lock(&ht->resize_mutex);
 576         _do_ht_resize(ht);
 577         pthread_mutex_unlock(&ht->resize_mutex);
 578         free(work);
 579 }
 580
 581 static
 582 void ht_resize_lazy(struct rcu_ht *ht, struct rcu_table *t, int growth)
 583 {
 584         struct rcu_resize_work *work;
 585         unsigned long target_size;
 586
 587         target_size = resize_target_update(t, growth);
 588         if (!CMM_LOAD_SHARED(t->resize_initiated) && t->size < target_size) {
 589                 work = malloc(sizeof(*work));
 590                 work->ht = ht;
 591                 ht->ht_call_rcu(&work->head, do_resize_cb);
 592                 CMM_STORE_SHARED(t->resize_initiated, 1);
 593         }
 594 }