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         void (*fct)(void *p);
 108         void *p;
 109
 110         /*
 111          * Tail is only modified when lock is held.
 112          * Head is only modified by owner thread.
 113          */
 114
 115         for (i = queue->tail; i != head;) {
 116                 smp_rmb();       /* read head before q[]. */
 117                 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
 118                 if (unlikely(DQ_IS_FCT_BIT(p))) {
 119                         //printf("%lu fct bit %p\n", i-1, p);
 120                         DQ_CLEAR_FCT_BIT(p);
 121                         queue->last_fct_out = p;
 122                         p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
 123                 } else if (unlikely(p == DQ_FCT_MARK)) {
 124                         //printf("%lu fct mark %p\n", i-1, p);
 125                         p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
 126                         queue->last_fct_out = p;
 127                         p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
 128                 }// else
 129                         //printf("%lu data %p\n", i-1, p);
 130                 fct = queue->last_fct_out;
 131                 //printf("tid %lu %lu last_fct %p data %p\n", pthread_self(), i-1, fct, p);
 132                 fct(p);
 133         }
 134         smp_mb();       /* push tail after having used q[] */
 135         STORE_SHARED(queue->tail, i);
 136 }
 137
 138 static void _rcu_defer_barrier_thread(void)
 139 {
 140         unsigned long head;
 141
 142         head = defer_queue.head;
 143         synchronize_rcu();
 144         rcu_defer_barrier_queue(&defer_queue, head);
 145 }
 146
 147
 148 void rcu_defer_barrier_thread(void)
 149 {
 150         internal_urcu_lock(&urcu_defer_mutex);
 151         _rcu_defer_barrier_thread();
 152         internal_urcu_unlock(&urcu_defer_mutex);
 153 }
 154
 155 void rcu_defer_barrier(void)
 156 {
 157         struct deferer_registry *index;
 158
 159         if (!registry)
 160                 return;
 161
 162         internal_urcu_lock(&urcu_defer_mutex);
 163         for (index = registry; index < registry + num_deferers; index++)
 164                 index->last_head = LOAD_SHARED(index->defer_queue->head);
 165         synchronize_rcu();
 166         for (index = registry; index < registry + num_deferers; index++)
 167                 rcu_defer_barrier_queue(index->defer_queue,
 168                                           index->last_head);
 169         internal_urcu_unlock(&urcu_defer_mutex);
 170 }
 171
 172 void *thr_defer(void *args)
 173 {
 174         for (;;) {
 175                 if (LOAD_SHARED(exit_defer))
 176                         break;
 177                 poll(NULL,0,100);       /* wait for 100ms */
 178                 rcu_defer_barrier();
 179         }
 180
 181         return NULL;
 182 }
 183
 184 /*
 185  * library wrappers to be used by non-LGPL compatible source code.
 186  */
 187
 188 void rcu_defer_queue(void (*fct)(void *p), void *p)
 189 {
 190         _rcu_defer_queue(fct, p);
 191 }
 192
 193 static void rcu_add_deferer(pthread_t id)
 194 {
 195         struct deferer_registry *oldarray;
 196
 197         if (!registry) {
 198                 alloc_deferers = INIT_NUM_THREADS;
 199                 num_deferers = 0;
 200                 registry =
 201                         malloc(sizeof(struct deferer_registry) * alloc_deferers);
 202         }
 203         if (alloc_deferers < num_deferers + 1) {
 204                 oldarray = registry;
 205                 registry = malloc(sizeof(struct deferer_registry)
 206                                 * (alloc_deferers << 1));
 207                 memcpy(registry, oldarray,
 208                         sizeof(struct deferer_registry) * alloc_deferers);
 209                 alloc_deferers <<= 1;
 210                 free(oldarray);
 211         }
 212         registry[num_deferers].tid = id;
 213         /* reference to the TLS of _this_ deferer thread. */
 214         registry[num_deferers].defer_queue = &defer_queue;
 215         registry[num_deferers].last_head = 0;
 216         num_deferers++;
 217 }
 218
 219 /*
 220  * Never shrink (implementation limitation).
 221  * This is O(nb threads). Eventually use a hash table.
 222  */
 223 static void rcu_remove_deferer(pthread_t id)
 224 {
 225         struct deferer_registry *index;
 226
 227         assert(registry != NULL);
 228         for (index = registry; index < registry + num_deferers; index++) {
 229                 if (pthread_equal(index->tid, id)) {
 230                         memcpy(index, &registry[num_deferers - 1],
 231                                 sizeof(struct deferer_registry));
 232                         registry[num_deferers - 1].tid = 0;
 233                         registry[num_deferers - 1].defer_queue = NULL;
 234                         registry[num_deferers - 1].last_head = 0;
 235                         num_deferers--;
 236                         return;
 237                 }
 238         }
 239         /* Hrm not found, forgot to register ? */
 240         assert(0);
 241 }
 242
 243 static void start_defer_thread(void)
 244 {
 245         int ret;
 246
 247         ret = pthread_create(&tid_defer, NULL, thr_defer,
 248                 NULL);
 249         assert(!ret);
 250 }
 251
 252 static void stop_defer_thread(void)
 253 {
 254         int ret;
 255         void *tret;
 256
 257         STORE_SHARED(exit_defer, 1);
 258         ret = pthread_join(tid_defer, &tret);
 259         assert(!ret);
 260 }
 261
 262 void rcu_defer_register_thread(void)
 263 {
 264         int deferers;
 265
 266         internal_urcu_lock(&defer_thread_mutex);
 267         internal_urcu_lock(&urcu_defer_mutex);
 268         defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
 269         rcu_add_deferer(pthread_self());
 270         deferers = num_deferers;
 271         internal_urcu_unlock(&urcu_defer_mutex);
 272
 273         if (deferers == 1)
 274                 start_defer_thread();
 275         internal_urcu_unlock(&defer_thread_mutex);
 276 }
 277
 278 void rcu_defer_unregister_thread(void)
 279 {
 280         int deferers;
 281
 282         internal_urcu_lock(&defer_thread_mutex);
 283         internal_urcu_lock(&urcu_defer_mutex);
 284         rcu_remove_deferer(pthread_self());
 285         _rcu_defer_barrier_thread();
 286         free(defer_queue.q);
 287         defer_queue.q = NULL;
 288         deferers = num_deferers;
 289         internal_urcu_unlock(&urcu_defer_mutex);
 290
 291         if (deferers == 0)
 292                 stop_defer_thread();
 293         internal_urcu_unlock(&defer_thread_mutex);
 294 }
 295
 296 void urcu_defer_exit(void)
 297 {
 298         free(registry);
 299 }