urcu-defer.c

   1 /*
   2  * urcu-defer.c
   3  *
   4  * Userspace RCU library - batch memory reclamation
   5  *
   6  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include <stdio.h>
  24 #include <pthread.h>
  25 #include <signal.h>
  26 #include <assert.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #include <errno.h>
  30 #include <poll.h>
  31
  32 #include "urcu-defer-static.h"
  33 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  34 #include "urcu-defer.h"
  35
  36 void __attribute__((destructor)) urcu_defer_exit(void);
  37
  38 extern void synchronize_rcu(void);
  39
  40 /*
  41  * urcu_defer_mutex nests inside defer_thread_mutex.
  42  */
  43 static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
  44 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
  45
  46 /*
  47  * Written to only by each individual deferer. Read by both the deferer and
  48  * the reclamation tread.
  49  */
  50 struct defer_queue __thread defer_queue;
  51
  52 /* Thread IDs of registered deferers */
  53 #define INIT_NUM_THREADS 4
  54
  55 struct deferer_registry {
  56         pthread_t tid;
  57         struct defer_queue *defer_queue;
  58         unsigned long last_head;
  59 };
  60
  61 static struct deferer_registry *registry;
  62 static int num_deferers, alloc_deferers;
  63
  64 static pthread_t tid_defer;
  65 static int exit_defer;
  66
  67 static void internal_urcu_lock(pthread_mutex_t *mutex)
  68 {
  69         int ret;
  70
  71 #ifndef DISTRUST_SIGNALS_EXTREME
  72         ret = pthread_mutex_lock(mutex);
  73         if (ret) {
  74                 perror("Error in pthread mutex lock");
  75                 exit(-1);
  76         }
  77 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
  78         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
  79                 if (ret != EBUSY && ret != EINTR) {
  80                         printf("ret = %d, errno = %d\n", ret, errno);
  81                         perror("Error in pthread mutex lock");
  82                         exit(-1);
  83                 }
  84                 poll(NULL,0,10);
  85         }
  86 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
  87 }
  88
  89 static void internal_urcu_unlock(pthread_mutex_t *mutex)
  90 {
  91         int ret;
  92
  93         ret = pthread_mutex_unlock(mutex);
  94         if (ret) {
  95                 perror("Error in pthread mutex unlock");
  96                 exit(-1);
  97         }
  98 }
  99
 100 /*
 101  * Must be called after Q.S. is reached.
 102  */
 103 static void rcu_defer_barrier_queue(struct defer_queue *queue,
 104                                       unsigned long head)
 105 {
 106         unsigned long i;
 107
 108         /*
 109          * Tail is only modified when lock is held.
 110          * Head is only modified by owner thread.
 111          */
 112
 113         for (i = queue->tail; i != head; i++) {
 114                 smp_rmb();       /* read head before q[]. */
 115                 free(LOAD_SHARED(queue->q[i & DEFER_QUEUE_MASK]));
 116         }
 117         smp_mb();       /* push tail after having used q[] */
 118         STORE_SHARED(queue->tail, i);
 119 }
 120
 121 static void _rcu_defer_barrier_thread(void)
 122 {
 123         unsigned long head;
 124
 125         head = defer_queue.head;
 126         synchronize_rcu();
 127         rcu_defer_barrier_queue(&defer_queue, head);
 128 }
 129
 130
 131 void rcu_defer_barrier_thread(void)
 132 {
 133         internal_urcu_lock(&urcu_defer_mutex);
 134         _rcu_defer_barrier_thread();
 135         internal_urcu_unlock(&urcu_defer_mutex);
 136 }
 137
 138 void rcu_defer_barrier(void)
 139 {
 140         struct deferer_registry *index;
 141
 142         if (!registry)
 143                 return;
 144
 145         internal_urcu_lock(&urcu_defer_mutex);
 146         for (index = registry; index < registry + num_deferers; index++)
 147                 index->last_head = LOAD_SHARED(index->defer_queue->head);
 148         synchronize_rcu();
 149         for (index = registry; index < registry + num_deferers; index++)
 150                 rcu_defer_barrier_queue(index->defer_queue,
 151                                           index->last_head);
 152         internal_urcu_unlock(&urcu_defer_mutex);
 153 }
 154
 155 void *thr_defer(void *args)
 156 {
 157         for (;;) {
 158                 if (LOAD_SHARED(exit_defer))
 159                         break;
 160                 poll(NULL,0,100);       /* wait for 100ms */
 161                 rcu_defer_barrier();
 162         }
 163
 164         return NULL;
 165 }
 166
 167 /*
 168  * library wrappers to be used by non-LGPL compatible source code.
 169  */
 170
 171 void rcu_defer_queue(void *p)
 172 {
 173         _rcu_defer_queue(p);
 174 }
 175
 176 static void rcu_add_deferer(pthread_t id)
 177 {
 178         struct deferer_registry *oldarray;
 179
 180         if (!registry) {
 181                 alloc_deferers = INIT_NUM_THREADS;
 182                 num_deferers = 0;
 183                 registry =
 184                         malloc(sizeof(struct deferer_registry) * alloc_deferers);
 185         }
 186         if (alloc_deferers < num_deferers + 1) {
 187                 oldarray = registry;
 188                 registry = malloc(sizeof(struct deferer_registry)
 189                                 * (alloc_deferers << 1));
 190                 memcpy(registry, oldarray,
 191                         sizeof(struct deferer_registry) * alloc_deferers);
 192                 alloc_deferers <<= 1;
 193                 free(oldarray);
 194         }
 195         registry[num_deferers].tid = id;
 196         /* reference to the TLS of _this_ deferer thread. */
 197         registry[num_deferers].defer_queue = &defer_queue;
 198         num_deferers++;
 199 }
 200
 201 /*
 202  * Never shrink (implementation limitation).
 203  * This is O(nb threads). Eventually use a hash table.
 204  */
 205 static void rcu_remove_deferer(pthread_t id)
 206 {
 207         struct deferer_registry *index;
 208
 209         assert(registry != NULL);
 210         for (index = registry; index < registry + num_deferers; index++) {
 211                 if (pthread_equal(index->tid, id)) {
 212                         memcpy(index, &registry[num_deferers - 1],
 213                                 sizeof(struct deferer_registry));
 214                         registry[num_deferers - 1].tid = 0;
 215                         registry[num_deferers - 1].defer_queue = NULL;
 216                         num_deferers--;
 217                         return;
 218                 }
 219         }
 220         /* Hrm not found, forgot to register ? */
 221         assert(0);
 222 }
 223
 224 static void start_defer_thread(void)
 225 {
 226         int ret;
 227
 228         ret = pthread_create(&tid_defer, NULL, thr_defer,
 229                 NULL);
 230         assert(!ret);
 231 }
 232
 233 static void stop_defer_thread(void)
 234 {
 235         int ret;
 236         void *tret;
 237
 238         STORE_SHARED(exit_defer, 1);
 239         ret = pthread_join(tid_defer, &tret);
 240         assert(!ret);
 241 }
 242
 243 void rcu_defer_register_thread(void)
 244 {
 245         int deferers;
 246
 247         internal_urcu_lock(&defer_thread_mutex);
 248         internal_urcu_lock(&urcu_defer_mutex);
 249         defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
 250         rcu_add_deferer(pthread_self());
 251         deferers = num_deferers;
 252         internal_urcu_unlock(&urcu_defer_mutex);
 253
 254         if (deferers == 1)
 255                 start_defer_thread();
 256         internal_urcu_unlock(&defer_thread_mutex);
 257 }
 258
 259 void rcu_defer_unregister_thread(void)
 260 {
 261         int deferers;
 262
 263         internal_urcu_lock(&defer_thread_mutex);
 264         internal_urcu_lock(&urcu_defer_mutex);
 265         rcu_remove_deferer(pthread_self());
 266         _rcu_defer_barrier_thread();
 267         free(defer_queue.q);
 268         defer_queue.q = NULL;
 269         deferers = num_deferers;
 270         internal_urcu_unlock(&urcu_defer_mutex);
 271
 272         if (deferers == 0)
 273                 stop_defer_thread();
 274         internal_urcu_unlock(&defer_thread_mutex);
 275 }
 276
 277 void urcu_defer_exit(void)
 278 {
 279         free(registry);
 280 }