urcu-qsbr.c

   1 /*
   2  * urcu.c
   3  *
   4  * Userspace RCU 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.h"
  36 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  37 //#include "urcu.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         char *need_mb;
  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 char __thread need_mb;
  68 static int num_readers, alloc_readers;
  69
  70 void internal_urcu_lock(void)
  71 {
  72         int ret;
  73
  74 #ifndef DISTRUST_SIGNALS_EXTREME
  75         ret = pthread_mutex_lock(&urcu_mutex);
  76         if (ret) {
  77                 perror("Error in pthread mutex lock");
  78                 exit(-1);
  79         }
  80 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
  81         while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
  82                 if (ret != EBUSY && ret != EINTR) {
  83                         printf("ret = %d, errno = %d\n", ret, errno);
  84                         perror("Error in pthread mutex lock");
  85                         exit(-1);
  86                 }
  87                 if (need_mb) {
  88                         smp_mb();
  89                         need_mb = 0;
  90                         smp_mb();
  91                 }
  92                 poll(NULL,0,10);
  93         }
  94 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
  95 }
  96
  97 void internal_urcu_unlock(void)
  98 {
  99         int ret;
 100
 101         ret = pthread_mutex_unlock(&urcu_mutex);
 102         if (ret) {
 103                 perror("Error in pthread mutex unlock");
 104                 exit(-1);
 105         }
 106 }
 107
 108 #ifdef HAS_INCOHERENT_CACHES
 109 static void force_mb_single_thread(struct reader_registry *index)
 110 {
 111         smp_mb();
 112 }
 113 #endif /* #ifdef HAS_INCOHERENT_CACHES */
 114
 115 static void force_mb_all_threads(void)
 116 {
 117         smp_mb();
 118 }
 119
 120 void wait_for_quiescent_state(void)
 121 {
 122         struct reader_registry *index;
 123
 124         if (!registry)
 125                 return;
 126         /*
 127          * Wait for each thread rcu_reader_qs_gp count to become 0.
 128          */
 129         for (index = registry; index < registry + num_readers; index++) {
 130 #ifndef HAS_INCOHERENT_CACHES
 131                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 132                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
 133                         cpu_relax();
 134 #else /* #ifndef HAS_INCOHERENT_CACHES */
 135                 int wait_loops = 0;
 136                 /*
 137                  * BUSY-LOOP. Force the reader thread to commit its
 138                  * rcu_reader_qs_gp update to memory if we wait for too long.
 139                  */
 140                 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
 141                        (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
 142                         if (wait_loops++ == KICK_READER_LOOPS) {
 143                                 force_mb_single_thread(index);
 144                                 wait_loops = 0;
 145                         } else {
 146                                 cpu_relax();
 147                         }
 148                 }
 149 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 150         }
 151 }
 152
 153 void synchronize_rcu(void)
 154 {
 155         internal_urcu_lock();
 156         force_mb_all_threads();
 157         urcu_gp_ctr += 2;
 158         wait_for_quiescent_state();
 159         force_mb_all_threads();
 160         internal_urcu_unlock();
 161 }
 162
 163 /*
 164  * library wrappers to be used by non-LGPL compatible source code.
 165  */
 166
 167 void rcu_read_lock(void)
 168 {
 169         _rcu_read_lock();
 170 }
 171
 172 void rcu_read_unlock(void)
 173 {
 174         _rcu_read_unlock();
 175 }
 176
 177 void *rcu_dereference(void *p)
 178 {
 179         return _rcu_dereference(p);
 180 }
 181
 182 void *rcu_assign_pointer_sym(void **p, void *v)
 183 {
 184         wmb();
 185         return STORE_SHARED(p, v);
 186 }
 187
 188 void *rcu_xchg_pointer_sym(void **p, void *v)
 189 {
 190         wmb();
 191         return xchg(p, v);
 192 }
 193
 194 void *rcu_publish_content_sym(void **p, void *v)
 195 {
 196         void *oldptr;
 197
 198         oldptr = _rcu_xchg_pointer(p, v);
 199         synchronize_rcu();
 200         return oldptr;
 201 }
 202
 203 static void rcu_add_reader(pthread_t id)
 204 {
 205         struct reader_registry *oldarray;
 206
 207         if (!registry) {
 208                 alloc_readers = INIT_NUM_THREADS;
 209                 num_readers = 0;
 210                 registry =
 211                         malloc(sizeof(struct reader_registry) * alloc_readers);
 212         }
 213         if (alloc_readers < num_readers + 1) {
 214                 oldarray = registry;
 215                 registry = malloc(sizeof(struct reader_registry)
 216                                 * (alloc_readers << 1));
 217                 memcpy(registry, oldarray,
 218                         sizeof(struct reader_registry) * alloc_readers);
 219                 alloc_readers <<= 1;
 220                 free(oldarray);
 221         }
 222         registry[num_readers].tid = id;
 223         /* reference to the TLS of _this_ reader thread. */
 224         registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
 225         registry[num_readers].need_mb = &need_mb;
 226         num_readers++;
 227 }
 228
 229 /*
 230  * Never shrink (implementation limitation).
 231  * This is O(nb threads). Eventually use a hash table.
 232  */
 233 static void rcu_remove_reader(pthread_t id)
 234 {
 235         struct reader_registry *index;
 236
 237         assert(registry != NULL);
 238         for (index = registry; index < registry + num_readers; index++) {
 239                 if (pthread_equal(index->tid, id)) {
 240                         memcpy(index, &registry[num_readers - 1],
 241                                 sizeof(struct reader_registry));
 242                         registry[num_readers - 1].tid = 0;
 243                         registry[num_readers - 1].rcu_reader_qs_gp = NULL;
 244                         num_readers--;
 245                         return;
 246                 }
 247         }
 248         /* Hrm not found, forgot to register ? */
 249         assert(0);
 250 }
 251
 252 void rcu_register_thread(void)
 253 {
 254         _rcu_thread_online();
 255         internal_urcu_lock();
 256         rcu_add_reader(pthread_self());
 257         internal_urcu_unlock();
 258 }
 259
 260 void rcu_unregister_thread(void)
 261 {
 262         /*
 263          * We have to make the thread offline otherwise we end up dealocking
 264          * with a waiting writer.
 265          */
 266         _rcu_thread_offline();
 267         internal_urcu_lock();
 268         rcu_remove_reader(pthread_self());
 269         internal_urcu_unlock();
 270 }