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 #define BUILD_QSBR_LIB
  36 #include "urcu-qsbr-static.h"
  37 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  38 #include "urcu-qsbr.h"
  39
  40 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
  41
  42 /*
  43  * Global grace period counter.
  44  */
  45 long urcu_gp_ctr = 0;
  46
  47 /*
  48  * Written to only by each individual reader. Read by both the reader and the
  49  * writers.
  50  */
  51 long __thread rcu_reader_qs_gp;
  52
  53 /* Thread IDs of registered readers */
  54 #define INIT_NUM_THREADS 4
  55
  56 struct reader_registry {
  57         pthread_t tid;
  58         long *rcu_reader_qs_gp;
  59 };
  60
  61 #ifdef DEBUG_YIELD
  62 unsigned int yield_active;
  63 unsigned int __thread rand_yield;
  64 #endif
  65
  66 static struct reader_registry *registry;
  67 static int num_readers, alloc_readers;
  68
  69 static void internal_urcu_lock(void)
  70 {
  71         int ret;
  72
  73 #ifndef DISTRUST_SIGNALS_EXTREME
  74         ret = pthread_mutex_lock(&urcu_mutex);
  75         if (ret) {
  76                 perror("Error in pthread mutex lock");
  77                 exit(-1);
  78         }
  79 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
  80         while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
  81                 if (ret != EBUSY && ret != EINTR) {
  82                         printf("ret = %d, errno = %d\n", ret, errno);
  83                         perror("Error in pthread mutex lock");
  84                         exit(-1);
  85                 }
  86                 poll(NULL,0,10);
  87         }
  88 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
  89 }
  90
  91 static void internal_urcu_unlock(void)
  92 {
  93         int ret;
  94
  95         ret = pthread_mutex_unlock(&urcu_mutex);
  96         if (ret) {
  97                 perror("Error in pthread mutex unlock");
  98                 exit(-1);
  99         }
 100 }
 101
 102 #ifdef HAS_INCOHERENT_CACHES
 103 static void force_mb_single_thread(struct reader_registry *index)
 104 {
 105         smp_mb();
 106 }
 107 #endif /* #ifdef HAS_INCOHERENT_CACHES */
 108
 109 static void force_mb_all_threads(void)
 110 {
 111         smp_mb();
 112 }
 113
 114 static void wait_for_quiescent_state(void)
 115 {
 116         struct reader_registry *index;
 117
 118         if (!registry)
 119                 return;
 120         /*
 121          * Wait for each thread rcu_reader_qs_gp count to become 0.
 122          */
 123         for (index = registry; index < registry + num_readers; index++) {
 124 #ifndef HAS_INCOHERENT_CACHES
 125                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 126                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
 127                         cpu_relax();
 128 #else /* #ifndef HAS_INCOHERENT_CACHES */
 129                 int wait_loops = 0;
 130                 /*
 131                  * BUSY-LOOP. Force the reader thread to commit its
 132                  * rcu_reader_qs_gp update to memory if we wait for too long.
 133                  */
 134                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 135                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
 136                         if (wait_loops++ == KICK_READER_LOOPS) {
 137                                 force_mb_single_thread(index);
 138                                 wait_loops = 0;
 139                         } else {
 140                                 cpu_relax();
 141                         }
 142                 }
 143 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 144         }
 145 }
 146
 147 void synchronize_rcu(void)
 148 {
 149         int was_online;
 150
 151         was_online = rcu_reader_qs_gp & 1;
 152
 153         /*
 154          * Mark the writer thread offline to make sure we don't wait for
 155          * our own quiescent state. This allows using synchronize_rcu() in
 156          * threads registered as readers.
 157          */
 158         if (was_online)
 159                 _rcu_thread_offline();
 160
 161         internal_urcu_lock();
 162         force_mb_all_threads();
 163         urcu_gp_ctr += 2;
 164         wait_for_quiescent_state();
 165         force_mb_all_threads();
 166         internal_urcu_unlock();
 167
 168         if (was_online)
 169                 _rcu_thread_online();
 170 }
 171
 172 /*
 173  * library wrappers to be used by non-LGPL compatible source code.
 174  */
 175
 176 void rcu_read_lock(void)
 177 {
 178         _rcu_read_lock();
 179 }
 180
 181 void rcu_read_unlock(void)
 182 {
 183         _rcu_read_unlock();
 184 }
 185
 186 void *rcu_dereference(void *p)
 187 {
 188         return _rcu_dereference(p);
 189 }
 190
 191 void *rcu_assign_pointer_sym(void **p, void *v)
 192 {
 193         wmb();
 194         return STORE_SHARED(p, v);
 195 }
 196
 197 void *rcu_xchg_pointer_sym(void **p, void *v)
 198 {
 199         wmb();
 200         return xchg(p, v);
 201 }
 202
 203 void *rcu_publish_content_sym(void **p, void *v)
 204 {
 205         void *oldptr;
 206
 207         oldptr = _rcu_xchg_pointer(p, v);
 208         synchronize_rcu();
 209         return oldptr;
 210 }
 211
 212 void rcu_quiescent_state(void)
 213 {
 214         _rcu_quiescent_state();
 215 }
 216
 217 void rcu_thread_offline(void)
 218 {
 219         _rcu_thread_offline();
 220 }
 221
 222 void rcu_thread_online(void)
 223 {
 224         _rcu_thread_online();
 225 }
 226
 227 static void rcu_add_reader(pthread_t id)
 228 {
 229         struct reader_registry *oldarray;
 230
 231         if (!registry) {
 232                 alloc_readers = INIT_NUM_THREADS;
 233                 num_readers = 0;
 234                 registry =
 235                         malloc(sizeof(struct reader_registry) * alloc_readers);
 236         }
 237         if (alloc_readers < num_readers + 1) {
 238                 oldarray = registry;
 239                 registry = malloc(sizeof(struct reader_registry)
 240                                 * (alloc_readers << 1));
 241                 memcpy(registry, oldarray,
 242                         sizeof(struct reader_registry) * alloc_readers);
 243                 alloc_readers <<= 1;
 244                 free(oldarray);
 245         }
 246         registry[num_readers].tid = id;
 247         /* reference to the TLS of _this_ reader thread. */
 248         registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
 249         num_readers++;
 250 }
 251
 252 /*
 253  * Never shrink (implementation limitation).
 254  * This is O(nb threads). Eventually use a hash table.
 255  */
 256 static void rcu_remove_reader(pthread_t id)
 257 {
 258         struct reader_registry *index;
 259
 260         assert(registry != NULL);
 261         for (index = registry; index < registry + num_readers; index++) {
 262                 if (pthread_equal(index->tid, id)) {
 263                         memcpy(index, &registry[num_readers - 1],
 264                                 sizeof(struct reader_registry));
 265                         registry[num_readers - 1].tid = 0;
 266                         registry[num_readers - 1].rcu_reader_qs_gp = NULL;
 267                         num_readers--;
 268                         return;
 269                 }
 270         }
 271         /* Hrm not found, forgot to register ? */
 272         assert(0);
 273 }
 274
 275 void rcu_register_thread(void)
 276 {
 277         internal_urcu_lock();
 278         rcu_add_reader(pthread_self());
 279         internal_urcu_unlock();
 280         _rcu_thread_online();
 281 }
 282
 283 void rcu_unregister_thread(void)
 284 {
 285         /*
 286          * We have to make the thread offline otherwise we end up dealocking
 287          * with a waiting writer.
 288          */
 289         _rcu_thread_offline();
 290         internal_urcu_lock();
 291         rcu_remove_reader(pthread_self());
 292         internal_urcu_unlock();
 293 }