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 unsigned long urcu_gp_ctr = 1;
  46
  47 /*
  48  * Written to only by each individual reader. Read by both the reader and the
  49  * writers.
  50  */
  51 unsigned 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         unsigned 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 wait_for_quiescent_state(void)
 110 {
 111         struct reader_registry *index;
 112
 113         if (!registry)
 114                 return;
 115         /*
 116          * Wait for each thread rcu_reader_qs_gp count to become 0.
 117          */
 118         for (index = registry; index < registry + num_readers; index++) {
 119 #ifndef HAS_INCOHERENT_CACHES
 120                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
 121                         cpu_relax();
 122 #else /* #ifndef HAS_INCOHERENT_CACHES */
 123                 int wait_loops = 0;
 124                 /*
 125                  * BUSY-LOOP. Force the reader thread to commit its
 126                  * rcu_reader_qs_gp update to memory if we wait for too long.
 127                  */
 128                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
 129                         if (wait_loops++ == KICK_READER_LOOPS) {
 130                                 force_mb_single_thread(index);
 131                                 wait_loops = 0;
 132                         } else {
 133                                 cpu_relax();
 134                         }
 135                 }
 136 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 137         }
 138 }
 139
 140 void synchronize_rcu(void)
 141 {
 142         unsigned long was_online;
 143
 144         was_online = rcu_reader_qs_gp;
 145
 146         /*
 147          * Mark the writer thread offline to make sure we don't wait for
 148          * our own quiescent state. This allows using synchronize_rcu() in
 149          * threads registered as readers.
 150          */
 151         smp_mb();
 152         if (was_online)
 153                 STORE_SHARED(rcu_reader_qs_gp, 0);
 154
 155         internal_urcu_lock();
 156         STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + 2);
 157         wait_for_quiescent_state();
 158         internal_urcu_unlock();
 159
 160         if (was_online)
 161                 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
 162         smp_mb();
 163 }
 164
 165 /*
 166  * library wrappers to be used by non-LGPL compatible source code.
 167  */
 168
 169 void rcu_read_lock(void)
 170 {
 171         _rcu_read_lock();
 172 }
 173
 174 void rcu_read_unlock(void)
 175 {
 176         _rcu_read_unlock();
 177 }
 178
 179 void *rcu_dereference(void *p)
 180 {
 181         return _rcu_dereference(p);
 182 }
 183
 184 void *rcu_assign_pointer_sym(void **p, void *v)
 185 {
 186         wmb();
 187         return STORE_SHARED(p, v);
 188 }
 189
 190 void *rcu_xchg_pointer_sym(void **p, void *v)
 191 {
 192         wmb();
 193         return xchg(p, v);
 194 }
 195
 196 void *rcu_publish_content_sym(void **p, void *v)
 197 {
 198         void *oldptr;
 199
 200         oldptr = _rcu_xchg_pointer(p, v);
 201         synchronize_rcu();
 202         return oldptr;
 203 }
 204
 205 void rcu_quiescent_state(void)
 206 {
 207         _rcu_quiescent_state();
 208 }
 209
 210 void rcu_thread_offline(void)
 211 {
 212         _rcu_thread_offline();
 213 }
 214
 215 void rcu_thread_online(void)
 216 {
 217         _rcu_thread_online();
 218 }
 219
 220 static void rcu_add_reader(pthread_t id)
 221 {
 222         struct reader_registry *oldarray;
 223
 224         if (!registry) {
 225                 alloc_readers = INIT_NUM_THREADS;
 226                 num_readers = 0;
 227                 registry =
 228                         malloc(sizeof(struct reader_registry) * alloc_readers);
 229         }
 230         if (alloc_readers < num_readers + 1) {
 231                 oldarray = registry;
 232                 registry = malloc(sizeof(struct reader_registry)
 233                                 * (alloc_readers << 1));
 234                 memcpy(registry, oldarray,
 235                         sizeof(struct reader_registry) * alloc_readers);
 236                 alloc_readers <<= 1;
 237                 free(oldarray);
 238         }
 239         registry[num_readers].tid = id;
 240         /* reference to the TLS of _this_ reader thread. */
 241         registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
 242         num_readers++;
 243 }
 244
 245 /*
 246  * Never shrink (implementation limitation).
 247  * This is O(nb threads). Eventually use a hash table.
 248  */
 249 static void rcu_remove_reader(pthread_t id)
 250 {
 251         struct reader_registry *index;
 252
 253         assert(registry != NULL);
 254         for (index = registry; index < registry + num_readers; index++) {
 255                 if (pthread_equal(index->tid, id)) {
 256                         memcpy(index, &registry[num_readers - 1],
 257                                 sizeof(struct reader_registry));
 258                         registry[num_readers - 1].tid = 0;
 259                         registry[num_readers - 1].rcu_reader_qs_gp = NULL;
 260                         num_readers--;
 261                         return;
 262                 }
 263         }
 264         /* Hrm not found, forgot to register ? */
 265         assert(0);
 266 }
 267
 268 void rcu_register_thread(void)
 269 {
 270         internal_urcu_lock();
 271         rcu_add_reader(pthread_self());
 272         internal_urcu_unlock();
 273         _rcu_thread_online();
 274 }
 275
 276 void rcu_unregister_thread(void)
 277 {
 278         /*
 279          * We have to make the thread offline otherwise we end up dealocking
 280          * with a waiting writer.
 281          */
 282         _rcu_thread_offline();
 283         internal_urcu_lock();
 284         rcu_remove_reader(pthread_self());
 285         internal_urcu_unlock();
 286 }