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-static.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 urcu_active_readers;
  51
  52 /* Thread IDs of registered readers */
  53 #define INIT_NUM_THREADS 4
  54
  55 struct reader_registry {
  56         pthread_t tid;
  57         long *urcu_active_readers;
  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 urcu_active_readers count to become 0.
 128          */
 129         for (index = registry; index < registry + num_readers; index++) {
 130 #ifndef HAS_INCOHERENT_CACHES
 131                 while (rcu_old_gp_ongoing(index->urcu_active_readers))
 132                         cpu_relax();
 133 #else /* #ifndef HAS_INCOHERENT_CACHES */
 134                 int wait_loops = 0;
 135                 /*
 136                  * BUSY-LOOP. Force the reader thread to commit its
 137                  * urcu_active_readers update to memory if we wait for too long.
 138                  */
 139                 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
 140                         if (wait_loops++ == KICK_READER_LOOPS) {
 141                                 force_mb_single_thread(index);
 142                                 wait_loops = 0;
 143                         } else {
 144                                 cpu_relax();
 145                         }
 146                 }
 147 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 148         }
 149 }
 150
 151 void synchronize_rcu(void)
 152 {
 153         internal_urcu_lock();
 154         force_mb_all_threads();
 155         urcu_gp_ctr += 2;
 156         wait_for_quiescent_state();
 157         force_mb_all_threads();
 158         internal_urcu_unlock();
 159 }
 160
 161 /*
 162  * library wrappers to be used by non-LGPL compatible source code.
 163  */
 164
 165 void rcu_read_lock(void)
 166 {
 167         _rcu_read_lock();
 168 }
 169
 170 void rcu_read_unlock(void)
 171 {
 172         _rcu_read_unlock();
 173 }
 174
 175 void *rcu_dereference(void *p)
 176 {
 177         return _rcu_dereference(p);
 178 }
 179
 180 void *rcu_assign_pointer_sym(void **p, void *v)
 181 {
 182         wmb();
 183         return STORE_SHARED(p, v);
 184 }
 185
 186 void *rcu_xchg_pointer_sym(void **p, void *v)
 187 {
 188         wmb();
 189         return xchg(p, v);
 190 }
 191
 192 void *rcu_publish_content_sym(void **p, void *v)
 193 {
 194         void *oldptr;
 195
 196         oldptr = _rcu_xchg_pointer(p, v);
 197         synchronize_rcu();
 198         return oldptr;
 199 }
 200
 201 static void rcu_add_reader(pthread_t id)
 202 {
 203         struct reader_registry *oldarray;
 204
 205         if (!registry) {
 206                 alloc_readers = INIT_NUM_THREADS;
 207                 num_readers = 0;
 208                 registry =
 209                         malloc(sizeof(struct reader_registry) * alloc_readers);
 210         }
 211         if (alloc_readers < num_readers + 1) {
 212                 oldarray = registry;
 213                 registry = malloc(sizeof(struct reader_registry)
 214                                 * (alloc_readers << 1));
 215                 memcpy(registry, oldarray,
 216                         sizeof(struct reader_registry) * alloc_readers);
 217                 alloc_readers <<= 1;
 218                 free(oldarray);
 219         }
 220         registry[num_readers].tid = id;
 221         /* reference to the TLS of _this_ reader thread. */
 222         registry[num_readers].urcu_active_readers = &urcu_active_readers;
 223         registry[num_readers].need_mb = &need_mb;
 224         num_readers++;
 225 }
 226
 227 /*
 228  * Never shrink (implementation limitation).
 229  * This is O(nb threads). Eventually use a hash table.
 230  */
 231 static void rcu_remove_reader(pthread_t id)
 232 {
 233         struct reader_registry *index;
 234
 235         assert(registry != NULL);
 236         for (index = registry; index < registry + num_readers; index++) {
 237                 if (pthread_equal(index->tid, id)) {
 238                         memcpy(index, &registry[num_readers - 1],
 239                                 sizeof(struct reader_registry));
 240                         registry[num_readers - 1].tid = 0;
 241                         registry[num_readers - 1].urcu_active_readers = NULL;
 242                         num_readers--;
 243                         return;
 244                 }
 245         }
 246         /* Hrm not found, forgot to register ? */
 247         assert(0);
 248 }
 249
 250 void rcu_register_thread(void)
 251 {
 252         internal_urcu_lock();
 253         rcu_add_reader(pthread_self());
 254         internal_urcu_unlock();
 255 }
 256
 257 void rcu_unregister_thread(void)
 258 {
 259         internal_urcu_lock();
 260         rcu_remove_reader(pthread_self());
 261         internal_urcu_unlock();
 262 }