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