urcu-qsbr.c

   1 /*
   2  * urcu-qsbr.c
   3  *
   4  * Userspace RCU QSBR library
   5  *
   6  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
   7  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  *
  23  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  24  */
  25
  26 #include <stdio.h>
  27 #include <pthread.h>
  28 #include <signal.h>
  29 #include <assert.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <errno.h>
  33 #include <poll.h>
  34
  35 #include "urcu-qsbr-static.h"
  36 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  37 #include "urcu-qsbr.h"
  38
  39 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
  40
  41 /*
  42  * Global grace period counter.
  43  */
  44 long urcu_gp_ctr = 0;
  45
  46 /*
  47  * Written to only by each individual reader. Read by both the reader and the
  48  * writers.
  49  */
  50 long __thread rcu_reader_qs_gp;
  51
  52 /* Thread IDs of registered readers */
  53 #define INIT_NUM_THREADS 4
  54
  55 struct reader_registry {
  56         pthread_t tid;
  57         long *rcu_reader_qs_gp;
  58 };
  59
  60 #ifdef DEBUG_YIELD
  61 unsigned int yield_active;
  62 unsigned int __thread rand_yield;
  63 #endif
  64
  65 static struct reader_registry *registry;
  66 static int num_readers, alloc_readers;
  67
  68 static void internal_urcu_lock(void)
  69 {
  70         int ret;
  71
  72 #ifndef DISTRUST_SIGNALS_EXTREME
  73         ret = pthread_mutex_lock(&urcu_mutex);
  74         if (ret) {
  75                 perror("Error in pthread mutex lock");
  76                 exit(-1);
  77         }
  78 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
  79         while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
  80                 if (ret != EBUSY && ret != EINTR) {
  81                         printf("ret = %d, errno = %d\n", ret, errno);
  82                         perror("Error in pthread mutex lock");
  83                         exit(-1);
  84                 }
  85                 poll(NULL,0,10);
  86         }
  87 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
  88 }
  89
  90 static void internal_urcu_unlock(void)
  91 {
  92         int ret;
  93
  94         ret = pthread_mutex_unlock(&urcu_mutex);
  95         if (ret) {
  96                 perror("Error in pthread mutex unlock");
  97                 exit(-1);
  98         }
  99 }
 100
 101 #ifdef HAS_INCOHERENT_CACHES
 102 static void force_mb_single_thread(struct reader_registry *index)
 103 {
 104         smp_mb();
 105 }
 106 #endif /* #ifdef HAS_INCOHERENT_CACHES */
 107
 108 static void force_mb_all_threads(void)
 109 {
 110         smp_mb();
 111 }
 112
 113 static void wait_for_quiescent_state(void)
 114 {
 115         struct reader_registry *index;
 116
 117         if (rcu_reader_qs_gp & 1)
 118             rcu_reader_qs_gp = urcu_gp_ctr + 1;
 119
 120         if (!registry)
 121                 return;
 122         /*
 123          * Wait for each thread rcu_reader_qs_gp count to become 0.
 124          */
 125         for (index = registry; index < registry + num_readers; index++) {
 126 #ifndef HAS_INCOHERENT_CACHES
 127                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 128                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
 129                         cpu_relax();
 130 #else /* #ifndef HAS_INCOHERENT_CACHES */
 131                 int wait_loops = 0;
 132                 /*
 133                  * BUSY-LOOP. Force the reader thread to commit its
 134                  * rcu_reader_qs_gp update to memory if we wait for too long.
 135                  */
 136                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 137                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
 138                         if (wait_loops++ == KICK_READER_LOOPS) {
 139                                 force_mb_single_thread(index);
 140                                 wait_loops = 0;
 141                         } else {
 142                                 cpu_relax();
 143                         }
 144                 }
 145 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 146         }
 147 }
 148
 149 void synchronize_rcu(void)
 150 {
 151         int was_online;
 152
 153         was_online = rcu_reader_qs_gp & 1;
 154
 155         /*
 156          * Mark the writer thread offline to make sure we don't wait for
 157          * our own quiescent state. This allows using synchronize_rcu() in
 158          * threads registered as readers.
 159          */
 160         if (was_online)
 161                 _rcu_thread_offline();
 162
 163         internal_urcu_lock();
 164         force_mb_all_threads();
 165         urcu_gp_ctr += 2;
 166         wait_for_quiescent_state();
 167         force_mb_all_threads();
 168         internal_urcu_unlock();
 169
 170         if (was_online)
 171                 _rcu_thread_online();
 172 }
 173
 174 /*
 175  * library wrappers to be used by non-LGPL compatible source code.
 176  */
 177
 178 void rcu_read_lock(void)
 179 {
 180         _rcu_read_lock();
 181 }
 182
 183 void rcu_read_unlock(void)
 184 {
 185         _rcu_read_unlock();
 186 }
 187
 188 void *rcu_dereference(void *p)
 189 {
 190         return _rcu_dereference(p);
 191 }
 192
 193 void *rcu_assign_pointer_sym(void **p, void *v)
 194 {
 195         wmb();
 196         return STORE_SHARED(p, v);
 197 }
 198
 199 void *rcu_xchg_pointer_sym(void **p, void *v)
 200 {
 201         wmb();
 202         return xchg(p, v);
 203 }
 204
 205 void *rcu_publish_content_sym(void **p, void *v)
 206 {
 207         void *oldptr;
 208
 209         oldptr = _rcu_xchg_pointer(p, v);
 210         synchronize_rcu();
 211         return oldptr;
 212 }
 213
 214 void rcu_quiescent_state(void)
 215 {
 216         _rcu_quiescent_state();
 217 }
 218
 219 void rcu_thread_offline(void)
 220 {
 221         _rcu_thread_offline();
 222 }
 223
 224 void rcu_thread_online(void)
 225 {
 226         _rcu_thread_online();
 227 }
 228
 229 static void rcu_add_reader(pthread_t id)
 230 {
 231         struct reader_registry *oldarray;
 232
 233         if (!registry) {
 234                 alloc_readers = INIT_NUM_THREADS;
 235                 num_readers = 0;
 236                 registry =
 237                         malloc(sizeof(struct reader_registry) * alloc_readers);
 238         }
 239         if (alloc_readers < num_readers + 1) {
 240                 oldarray = registry;
 241                 registry = malloc(sizeof(struct reader_registry)
 242                                 * (alloc_readers << 1));
 243                 memcpy(registry, oldarray,
 244                         sizeof(struct reader_registry) * alloc_readers);
 245                 alloc_readers <<= 1;
 246                 free(oldarray);
 247         }
 248         registry[num_readers].tid = id;
 249         /* reference to the TLS of _this_ reader thread. */
 250         registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
 251         num_readers++;
 252 }
 253
 254 /*
 255  * Never shrink (implementation limitation).
 256  * This is O(nb threads). Eventually use a hash table.
 257  */
 258 static void rcu_remove_reader(pthread_t id)
 259 {
 260         struct reader_registry *index;
 261
 262         assert(registry != NULL);
 263         for (index = registry; index < registry + num_readers; index++) {
 264                 if (pthread_equal(index->tid, id)) {
 265                         memcpy(index, &registry[num_readers - 1],
 266                                 sizeof(struct reader_registry));
 267                         registry[num_readers - 1].tid = 0;
 268                         registry[num_readers - 1].rcu_reader_qs_gp = NULL;
 269                         num_readers--;
 270                         return;
 271                 }
 272         }
 273         /* Hrm not found, forgot to register ? */
 274         assert(0);
 275 }
 276
 277 void rcu_register_thread(void)
 278 {
 279         internal_urcu_lock();
 280         rcu_add_reader(pthread_self());
 281         internal_urcu_unlock();
 282         _rcu_thread_online();
 283 }
 284
 285 void rcu_unregister_thread(void)
 286 {
 287         /*
 288          * We have to make the thread offline otherwise we end up dealocking
 289          * with a waiting writer.
 290          */
 291         _rcu_thread_offline();
 292         internal_urcu_lock();
 293         rcu_remove_reader(pthread_self());
 294         internal_urcu_unlock();
 295 }