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 (!registry)
 118                 return;
 119         /*
 120          * Wait for each thread rcu_reader_qs_gp count to become 0.
 121          */
 122         for (index = registry; index < registry + num_readers; index++) {
 123 #ifndef HAS_INCOHERENT_CACHES
 124                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 125                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
 126                         cpu_relax();
 127 #else /* #ifndef HAS_INCOHERENT_CACHES */
 128                 int wait_loops = 0;
 129                 /*
 130                  * BUSY-LOOP. Force the reader thread to commit its
 131                  * rcu_reader_qs_gp update to memory if we wait for too long.
 132                  */
 133                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 134                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
 135                         if (wait_loops++ == KICK_READER_LOOPS) {
 136                                 force_mb_single_thread(index);
 137                                 wait_loops = 0;
 138                         } else {
 139                                 cpu_relax();
 140                         }
 141                 }
 142 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 143         }
 144 }
 145
 146 void synchronize_rcu(void)
 147 {
 148         int was_online;
 149
 150         was_online = rcu_reader_qs_gp & 1;
 151
 152         /*
 153          * Mark the writer thread offline to make sure we don't wait for
 154          * our own quiescent state. This allows using synchronize_rcu() in
 155          * threads registered as readers.
 156          */
 157         if (was_online)
 158                 _rcu_thread_offline();
 159
 160         internal_urcu_lock();
 161         force_mb_all_threads();
 162         urcu_gp_ctr += 2;
 163         wait_for_quiescent_state();
 164         force_mb_all_threads();
 165         internal_urcu_unlock();
 166
 167         if (was_online)
 168                 _rcu_thread_online();
 169 }
 170
 171 /*
 172  * library wrappers to be used by non-LGPL compatible source code.
 173  */
 174
 175 void rcu_read_lock(void)
 176 {
 177         _rcu_read_lock();
 178 }
 179
 180 void rcu_read_unlock(void)
 181 {
 182         _rcu_read_unlock();
 183 }
 184
 185 void *rcu_dereference(void *p)
 186 {
 187         return _rcu_dereference(p);
 188 }
 189
 190 void *rcu_assign_pointer_sym(void **p, void *v)
 191 {
 192         wmb();
 193         return STORE_SHARED(p, v);
 194 }
 195
 196 void *rcu_xchg_pointer_sym(void **p, void *v)
 197 {
 198         wmb();
 199         return xchg(p, v);
 200 }
 201
 202 void *rcu_publish_content_sym(void **p, void *v)
 203 {
 204         void *oldptr;
 205
 206         oldptr = _rcu_xchg_pointer(p, v);
 207         synchronize_rcu();
 208         return oldptr;
 209 }
 210
 211 void rcu_quiescent_state(void)
 212 {
 213         _rcu_quiescent_state();
 214 }
 215
 216 void rcu_thread_offline(void)
 217 {
 218         _rcu_thread_offline();
 219 }
 220
 221 void rcu_thread_online(void)
 222 {
 223         _rcu_thread_online();
 224 }
 225
 226 static void rcu_add_reader(pthread_t id)
 227 {
 228         struct reader_registry *oldarray;
 229
 230         if (!registry) {
 231                 alloc_readers = INIT_NUM_THREADS;
 232                 num_readers = 0;
 233                 registry =
 234                         malloc(sizeof(struct reader_registry) * alloc_readers);
 235         }
 236         if (alloc_readers < num_readers + 1) {
 237                 oldarray = registry;
 238                 registry = malloc(sizeof(struct reader_registry)
 239                                 * (alloc_readers << 1));
 240                 memcpy(registry, oldarray,
 241                         sizeof(struct reader_registry) * alloc_readers);
 242                 alloc_readers <<= 1;
 243                 free(oldarray);
 244         }
 245         registry[num_readers].tid = id;
 246         /* reference to the TLS of _this_ reader thread. */
 247         registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
 248         num_readers++;
 249 }
 250
 251 /*
 252  * Never shrink (implementation limitation).
 253  * This is O(nb threads). Eventually use a hash table.
 254  */
 255 static void rcu_remove_reader(pthread_t id)
 256 {
 257         struct reader_registry *index;
 258
 259         assert(registry != NULL);
 260         for (index = registry; index < registry + num_readers; index++) {
 261                 if (pthread_equal(index->tid, id)) {
 262                         memcpy(index, &registry[num_readers - 1],
 263                                 sizeof(struct reader_registry));
 264                         registry[num_readers - 1].tid = 0;
 265                         registry[num_readers - 1].rcu_reader_qs_gp = NULL;
 266                         num_readers--;
 267                         return;
 268                 }
 269         }
 270         /* Hrm not found, forgot to register ? */
 271         assert(0);
 272 }
 273
 274 void rcu_register_thread(void)
 275 {
 276         internal_urcu_lock();
 277         rcu_add_reader(pthread_self());
 278         internal_urcu_unlock();
 279         _rcu_thread_online();
 280 }
 281
 282 void rcu_unregister_thread(void)
 283 {
 284         /*
 285          * We have to make the thread offline otherwise we end up dealocking
 286          * with a waiting writer.
 287          */
 288         _rcu_thread_offline();
 289         internal_urcu_lock();
 290         rcu_remove_reader(pthread_self());
 291         internal_urcu_unlock();
 292 }