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, num_items;
 137
 138         head = defer_queue.head;
 139         num_items = head - defer_queue.tail;
 140         if (unlikely(!num_items))
 141                 return;
 142         synchronize_rcu();
 143         rcu_defer_barrier_queue(&defer_queue, head);
 144 }
 145
 146
 147 void rcu_defer_barrier_thread(void)
 148 {
 149         internal_urcu_lock(&urcu_defer_mutex);
 150         _rcu_defer_barrier_thread();
 151         internal_urcu_unlock(&urcu_defer_mutex);
 152 }
 153
 154 /*
 155  * rcu_defer_barrier - Execute all queued rcu callbacks.
 156  *
 157  * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
 158  * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
 159  * are guaranteed to be executed.
 160  * Callbacks queued by other threads concurrently with rcu_defer_barrier()
 161  * execution are not guaranteed to be executed in the current batch (could
 162  * be left for the next batch). These callbacks queued by other threads are only
 163  * guaranteed to be executed if there is explicit synchronization between
 164  * the thread adding to the queue and the thread issuing the defer_barrier call.
 165  */
 166
 167 void rcu_defer_barrier(void)
 168 {
 169         struct deferer_registry *index;
 170         unsigned long num_items = 0;
 171
 172         if (!registry)
 173                 return;
 174
 175         internal_urcu_lock(&urcu_defer_mutex);
 176         for (index = registry; index < registry + num_deferers; index++) {
 177                 index->last_head = LOAD_SHARED(index->defer_queue->head);
 178                 num_items += index->last_head - index->defer_queue->tail;
 179         }
 180         if (likely(!num_items)) {
 181                 /*
 182                  * We skip the grace period because there are no queued
 183                  * callbacks to execute.
 184                  */
 185                 goto end;
 186         }
 187         synchronize_rcu();
 188         for (index = registry; index < registry + num_deferers; index++)
 189                 rcu_defer_barrier_queue(index->defer_queue,
 190                                           index->last_head);
 191 end:
 192         internal_urcu_unlock(&urcu_defer_mutex);
 193 }
 194
 195 void *thr_defer(void *args)
 196 {
 197         for (;;) {
 198                 if (LOAD_SHARED(exit_defer))
 199                         break;
 200                 poll(NULL,0,100);       /* wait for 100ms */
 201                 rcu_defer_barrier();
 202         }
 203
 204         return NULL;
 205 }
 206
 207 /*
 208  * library wrappers to be used by non-LGPL compatible source code.
 209  */
 210
 211 void rcu_defer_queue(void (*fct)(void *p), void *p)
 212 {
 213         _rcu_defer_queue(fct, p);
 214 }
 215
 216 static void rcu_add_deferer(pthread_t id)
 217 {
 218         struct deferer_registry *oldarray;
 219
 220         if (!registry) {
 221                 alloc_deferers = INIT_NUM_THREADS;
 222                 num_deferers = 0;
 223                 registry =
 224                         malloc(sizeof(struct deferer_registry) * alloc_deferers);
 225         }
 226         if (alloc_deferers < num_deferers + 1) {
 227                 oldarray = registry;
 228                 registry = malloc(sizeof(struct deferer_registry)
 229                                 * (alloc_deferers << 1));
 230                 memcpy(registry, oldarray,
 231                         sizeof(struct deferer_registry) * alloc_deferers);
 232                 alloc_deferers <<= 1;
 233                 free(oldarray);
 234         }
 235         registry[num_deferers].tid = id;
 236         /* reference to the TLS of _this_ deferer thread. */
 237         registry[num_deferers].defer_queue = &defer_queue;
 238         registry[num_deferers].last_head = 0;
 239         num_deferers++;
 240 }
 241
 242 /*
 243  * Never shrink (implementation limitation).
 244  * This is O(nb threads). Eventually use a hash table.
 245  */
 246 static void rcu_remove_deferer(pthread_t id)
 247 {
 248         struct deferer_registry *index;
 249
 250         assert(registry != NULL);
 251         for (index = registry; index < registry + num_deferers; index++) {
 252                 if (pthread_equal(index->tid, id)) {
 253                         memcpy(index, &registry[num_deferers - 1],
 254                                 sizeof(struct deferer_registry));
 255                         registry[num_deferers - 1].tid = 0;
 256                         registry[num_deferers - 1].defer_queue = NULL;
 257                         registry[num_deferers - 1].last_head = 0;
 258                         num_deferers--;
 259                         return;
 260                 }
 261         }
 262         /* Hrm not found, forgot to register ? */
 263         assert(0);
 264 }
 265
 266 static void start_defer_thread(void)
 267 {
 268         int ret;
 269
 270         ret = pthread_create(&tid_defer, NULL, thr_defer,
 271                 NULL);
 272         assert(!ret);
 273 }
 274
 275 static void stop_defer_thread(void)
 276 {
 277         int ret;
 278         void *tret;
 279
 280         STORE_SHARED(exit_defer, 1);
 281         ret = pthread_join(tid_defer, &tret);
 282         assert(!ret);
 283 }
 284
 285 void rcu_defer_register_thread(void)
 286 {
 287         int deferers;
 288
 289         internal_urcu_lock(&defer_thread_mutex);
 290         internal_urcu_lock(&urcu_defer_mutex);
 291         defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
 292         rcu_add_deferer(pthread_self());
 293         deferers = num_deferers;
 294         internal_urcu_unlock(&urcu_defer_mutex);
 295
 296         if (deferers == 1)
 297                 start_defer_thread();
 298         internal_urcu_unlock(&defer_thread_mutex);
 299 }
 300
 301 void rcu_defer_unregister_thread(void)
 302 {
 303         int deferers;
 304
 305         internal_urcu_lock(&defer_thread_mutex);
 306         internal_urcu_lock(&urcu_defer_mutex);
 307         rcu_remove_deferer(pthread_self());
 308         _rcu_defer_barrier_thread();
 309         free(defer_queue.q);
 310         defer_queue.q = NULL;
 311         deferers = num_deferers;
 312         internal_urcu_unlock(&urcu_defer_mutex);
 313
 314         if (deferers == 0)
 315                 stop_defer_thread();
 316         internal_urcu_unlock(&defer_thread_mutex);
 317 }
 318
 319 void urcu_defer_exit(void)
 320 {
 321         free(registry);
 322 }