| 1 | /* |
| 2 | * urcu-reclaim.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-reclaim-static.h" |
| 33 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
| 34 | #include "urcu-reclaim.h" |
| 35 | |
| 36 | void __attribute__((destructor)) urcu_reclaim_exit(void); |
| 37 | |
| 38 | extern void synchronize_rcu(void); |
| 39 | |
| 40 | /* |
| 41 | * urcu_reclaim_mutex nests inside reclaim_thread_mutex. |
| 42 | */ |
| 43 | static pthread_mutex_t urcu_reclaim_mutex = PTHREAD_MUTEX_INITIALIZER; |
| 44 | static pthread_mutex_t reclaim_thread_mutex = PTHREAD_MUTEX_INITIALIZER; |
| 45 | |
| 46 | /* |
| 47 | * Written to only by each individual reclaimer. Read by both the reclaimer and |
| 48 | * the reclamation tread. |
| 49 | */ |
| 50 | struct reclaim_queue __thread reclaim_queue; |
| 51 | |
| 52 | /* Thread IDs of registered reclaimers */ |
| 53 | #define INIT_NUM_THREADS 4 |
| 54 | |
| 55 | struct reclaimer_registry { |
| 56 | pthread_t tid; |
| 57 | struct reclaim_queue *reclaim_queue; |
| 58 | unsigned long last_head; |
| 59 | }; |
| 60 | |
| 61 | static struct reclaimer_registry *registry; |
| 62 | static int num_reclaimers, alloc_reclaimers; |
| 63 | |
| 64 | static pthread_t tid_reclaim; |
| 65 | static int exit_reclaim; |
| 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_reclaim_barrier_queue(struct reclaim_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 & RECLAIM_QUEUE_MASK])); |
| 116 | } |
| 117 | smp_mb(); /* push tail after having used q[] */ |
| 118 | STORE_SHARED(queue->tail, i); |
| 119 | } |
| 120 | |
| 121 | static void _rcu_reclaim_barrier_thread(void) |
| 122 | { |
| 123 | unsigned long head; |
| 124 | |
| 125 | head = reclaim_queue.head; |
| 126 | synchronize_rcu(); |
| 127 | rcu_reclaim_barrier_queue(&reclaim_queue, head); |
| 128 | } |
| 129 | |
| 130 | |
| 131 | void rcu_reclaim_barrier_thread(void) |
| 132 | { |
| 133 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 134 | _rcu_reclaim_barrier_thread(); |
| 135 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 136 | } |
| 137 | |
| 138 | void rcu_reclaim_barrier(void) |
| 139 | { |
| 140 | struct reclaimer_registry *index; |
| 141 | |
| 142 | if (!registry) |
| 143 | return; |
| 144 | |
| 145 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 146 | for (index = registry; index < registry + num_reclaimers; index++) |
| 147 | index->last_head = LOAD_SHARED(index->reclaim_queue->head); |
| 148 | synchronize_rcu(); |
| 149 | for (index = registry; index < registry + num_reclaimers; index++) |
| 150 | rcu_reclaim_barrier_queue(index->reclaim_queue, |
| 151 | index->last_head); |
| 152 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 153 | } |
| 154 | |
| 155 | void *thr_reclaim(void *args) |
| 156 | { |
| 157 | for (;;) { |
| 158 | if (LOAD_SHARED(exit_reclaim)) |
| 159 | break; |
| 160 | poll(NULL,0,100); /* wait for 100ms */ |
| 161 | rcu_reclaim_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_reclaim_queue(void *p) |
| 172 | { |
| 173 | _rcu_reclaim_queue(p); |
| 174 | } |
| 175 | |
| 176 | static void rcu_add_reclaimer(pthread_t id) |
| 177 | { |
| 178 | struct reclaimer_registry *oldarray; |
| 179 | |
| 180 | if (!registry) { |
| 181 | alloc_reclaimers = INIT_NUM_THREADS; |
| 182 | num_reclaimers = 0; |
| 183 | registry = |
| 184 | malloc(sizeof(struct reclaimer_registry) * alloc_reclaimers); |
| 185 | } |
| 186 | if (alloc_reclaimers < num_reclaimers + 1) { |
| 187 | oldarray = registry; |
| 188 | registry = malloc(sizeof(struct reclaimer_registry) |
| 189 | * (alloc_reclaimers << 1)); |
| 190 | memcpy(registry, oldarray, |
| 191 | sizeof(struct reclaimer_registry) * alloc_reclaimers); |
| 192 | alloc_reclaimers <<= 1; |
| 193 | free(oldarray); |
| 194 | } |
| 195 | registry[num_reclaimers].tid = id; |
| 196 | /* reference to the TLS of _this_ reclaimer thread. */ |
| 197 | registry[num_reclaimers].reclaim_queue = &reclaim_queue; |
| 198 | num_reclaimers++; |
| 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_reclaimer(pthread_t id) |
| 206 | { |
| 207 | struct reclaimer_registry *index; |
| 208 | |
| 209 | assert(registry != NULL); |
| 210 | for (index = registry; index < registry + num_reclaimers; index++) { |
| 211 | if (pthread_equal(index->tid, id)) { |
| 212 | memcpy(index, ®istry[num_reclaimers - 1], |
| 213 | sizeof(struct reclaimer_registry)); |
| 214 | registry[num_reclaimers - 1].tid = 0; |
| 215 | registry[num_reclaimers - 1].reclaim_queue = NULL; |
| 216 | num_reclaimers--; |
| 217 | return; |
| 218 | } |
| 219 | } |
| 220 | /* Hrm not found, forgot to register ? */ |
| 221 | assert(0); |
| 222 | } |
| 223 | |
| 224 | static void start_reclaim_thread(void) |
| 225 | { |
| 226 | int ret; |
| 227 | |
| 228 | ret = pthread_create(&tid_reclaim, NULL, thr_reclaim, |
| 229 | NULL); |
| 230 | assert(!ret); |
| 231 | } |
| 232 | |
| 233 | static void stop_reclaim_thread(void) |
| 234 | { |
| 235 | int ret; |
| 236 | void *tret; |
| 237 | |
| 238 | STORE_SHARED(exit_reclaim, 1); |
| 239 | ret = pthread_join(tid_reclaim, &tret); |
| 240 | assert(!ret); |
| 241 | } |
| 242 | |
| 243 | void rcu_reclaim_register_thread(void) |
| 244 | { |
| 245 | int reclaimers; |
| 246 | |
| 247 | internal_urcu_lock(&reclaim_thread_mutex); |
| 248 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 249 | reclaim_queue.q = malloc(sizeof(void *) * RECLAIM_QUEUE_SIZE); |
| 250 | rcu_add_reclaimer(pthread_self()); |
| 251 | reclaimers = num_reclaimers; |
| 252 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 253 | |
| 254 | if (reclaimers == 1) |
| 255 | start_reclaim_thread(); |
| 256 | internal_urcu_unlock(&reclaim_thread_mutex); |
| 257 | } |
| 258 | |
| 259 | void rcu_reclaim_unregister_thread(void) |
| 260 | { |
| 261 | int reclaimers; |
| 262 | |
| 263 | internal_urcu_lock(&reclaim_thread_mutex); |
| 264 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 265 | rcu_remove_reclaimer(pthread_self()); |
| 266 | _rcu_reclaim_barrier_thread(); |
| 267 | free(reclaim_queue.q); |
| 268 | reclaim_queue.q = NULL; |
| 269 | reclaimers = num_reclaimers; |
| 270 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 271 | |
| 272 | if (reclaimers == 0) |
| 273 | stop_reclaim_thread(); |
| 274 | internal_urcu_unlock(&reclaim_thread_mutex); |
| 275 | } |
| 276 | |
| 277 | void urcu_reclaim_exit(void) |
| 278 | { |
| 279 | free(registry); |
| 280 | } |