| 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__((constructor)) urcu_reclaim_init(void); |
| 37 | void __attribute__((destructor)) urcu_reclaim_exit(void); |
| 38 | |
| 39 | extern void synchronize_rcu(void); |
| 40 | |
| 41 | static int init_done; |
| 42 | |
| 43 | /* |
| 44 | * urcu_reclaim_mutex nests inside reclaim_thread_mutex. |
| 45 | */ |
| 46 | static pthread_mutex_t urcu_reclaim_mutex = PTHREAD_MUTEX_INITIALIZER; |
| 47 | static pthread_mutex_t reclaim_thread_mutex = PTHREAD_MUTEX_INITIALIZER; |
| 48 | |
| 49 | /* |
| 50 | * Written to only by each individual reader. Read by both the reader and the |
| 51 | * writers. |
| 52 | */ |
| 53 | struct reclaim_queue __thread reclaim_queue; |
| 54 | |
| 55 | /* Thread IDs of registered readers */ |
| 56 | #define INIT_NUM_THREADS 4 |
| 57 | |
| 58 | struct reader_registry { |
| 59 | pthread_t tid; |
| 60 | struct reclaim_queue *reclaim_queue; |
| 61 | unsigned long last_head; |
| 62 | }; |
| 63 | |
| 64 | static struct reader_registry *registry; |
| 65 | static int num_readers, alloc_readers; |
| 66 | |
| 67 | static pthread_t tid_reclaim; |
| 68 | static int exit_reclaim; |
| 69 | |
| 70 | static void internal_urcu_lock(pthread_mutex_t *mutex) |
| 71 | { |
| 72 | int ret; |
| 73 | |
| 74 | #ifndef DISTRUST_SIGNALS_EXTREME |
| 75 | ret = pthread_mutex_lock(mutex); |
| 76 | if (ret) { |
| 77 | perror("Error in pthread mutex lock"); |
| 78 | exit(-1); |
| 79 | } |
| 80 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
| 81 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
| 82 | if (ret != EBUSY && ret != EINTR) { |
| 83 | printf("ret = %d, errno = %d\n", ret, errno); |
| 84 | perror("Error in pthread mutex lock"); |
| 85 | exit(-1); |
| 86 | } |
| 87 | poll(NULL,0,10); |
| 88 | } |
| 89 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ |
| 90 | } |
| 91 | |
| 92 | static void internal_urcu_unlock(pthread_mutex_t *mutex) |
| 93 | { |
| 94 | int ret; |
| 95 | |
| 96 | ret = pthread_mutex_unlock(mutex); |
| 97 | if (ret) { |
| 98 | perror("Error in pthread mutex unlock"); |
| 99 | exit(-1); |
| 100 | } |
| 101 | } |
| 102 | |
| 103 | /* |
| 104 | * Must be called after Q.S. is reached. |
| 105 | */ |
| 106 | static void rcu_reclaim_barrier_queue(struct reclaim_queue *queue, |
| 107 | unsigned long head) |
| 108 | { |
| 109 | unsigned long i; |
| 110 | |
| 111 | /* |
| 112 | * Tail is only modified when lock is held. |
| 113 | * Head is only modified by owner thread. |
| 114 | */ |
| 115 | |
| 116 | for (i = queue->tail; i != head; i++) { |
| 117 | smp_rmb(); /* read head before q[]. */ |
| 118 | free(LOAD_SHARED(queue->q[i & RECLAIM_QUEUE_MASK])); |
| 119 | } |
| 120 | smp_mb(); /* push tail after having used q[] */ |
| 121 | STORE_SHARED(queue->tail, i); |
| 122 | } |
| 123 | |
| 124 | static void _rcu_reclaim_barrier_thread(void) |
| 125 | { |
| 126 | unsigned long head; |
| 127 | |
| 128 | head = reclaim_queue.head; |
| 129 | synchronize_rcu(); |
| 130 | rcu_reclaim_barrier_queue(&reclaim_queue, head); |
| 131 | } |
| 132 | |
| 133 | |
| 134 | void rcu_reclaim_barrier_thread(void) |
| 135 | { |
| 136 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 137 | _rcu_reclaim_barrier_thread(); |
| 138 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 139 | } |
| 140 | |
| 141 | void rcu_reclaim_barrier(void) |
| 142 | { |
| 143 | struct reader_registry *index; |
| 144 | |
| 145 | if (!registry) |
| 146 | return; |
| 147 | |
| 148 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 149 | for (index = registry; index < registry + num_readers; index++) |
| 150 | index->last_head = LOAD_SHARED(index->reclaim_queue->head); |
| 151 | synchronize_rcu(); |
| 152 | for (index = registry; index < registry + num_readers; index++) |
| 153 | rcu_reclaim_barrier_queue(index->reclaim_queue, |
| 154 | index->last_head); |
| 155 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 156 | } |
| 157 | |
| 158 | void *thr_reclaim(void *args) |
| 159 | { |
| 160 | for (;;) { |
| 161 | if (LOAD_SHARED(exit_reclaim)) |
| 162 | break; |
| 163 | poll(NULL,0,100); /* wait for 100ms */ |
| 164 | rcu_reclaim_barrier(); |
| 165 | } |
| 166 | |
| 167 | return NULL; |
| 168 | } |
| 169 | |
| 170 | /* |
| 171 | * library wrappers to be used by non-LGPL compatible source code. |
| 172 | */ |
| 173 | |
| 174 | void rcu_reclaim_queue(void *p) |
| 175 | { |
| 176 | _rcu_reclaim_queue(p); |
| 177 | } |
| 178 | |
| 179 | static void rcu_add_reader(pthread_t id) |
| 180 | { |
| 181 | struct reader_registry *oldarray; |
| 182 | |
| 183 | if (!registry) { |
| 184 | alloc_readers = INIT_NUM_THREADS; |
| 185 | num_readers = 0; |
| 186 | registry = |
| 187 | malloc(sizeof(struct reader_registry) * alloc_readers); |
| 188 | } |
| 189 | if (alloc_readers < num_readers + 1) { |
| 190 | oldarray = registry; |
| 191 | registry = malloc(sizeof(struct reader_registry) |
| 192 | * (alloc_readers << 1)); |
| 193 | memcpy(registry, oldarray, |
| 194 | sizeof(struct reader_registry) * alloc_readers); |
| 195 | alloc_readers <<= 1; |
| 196 | free(oldarray); |
| 197 | } |
| 198 | registry[num_readers].tid = id; |
| 199 | /* reference to the TLS of _this_ reader thread. */ |
| 200 | registry[num_readers].reclaim_queue = &reclaim_queue; |
| 201 | num_readers++; |
| 202 | } |
| 203 | |
| 204 | /* |
| 205 | * Never shrink (implementation limitation). |
| 206 | * This is O(nb threads). Eventually use a hash table. |
| 207 | */ |
| 208 | static void rcu_remove_reader(pthread_t id) |
| 209 | { |
| 210 | struct reader_registry *index; |
| 211 | |
| 212 | assert(registry != NULL); |
| 213 | for (index = registry; index < registry + num_readers; index++) { |
| 214 | if (pthread_equal(index->tid, id)) { |
| 215 | memcpy(index, ®istry[num_readers - 1], |
| 216 | sizeof(struct reader_registry)); |
| 217 | registry[num_readers - 1].tid = 0; |
| 218 | registry[num_readers - 1].reclaim_queue = NULL; |
| 219 | num_readers--; |
| 220 | return; |
| 221 | } |
| 222 | } |
| 223 | /* Hrm not found, forgot to register ? */ |
| 224 | assert(0); |
| 225 | } |
| 226 | |
| 227 | static void start_reclaim_thread(void) |
| 228 | { |
| 229 | int ret; |
| 230 | |
| 231 | ret = pthread_create(&tid_reclaim, NULL, thr_reclaim, |
| 232 | NULL); |
| 233 | assert(!ret); |
| 234 | } |
| 235 | |
| 236 | static void stop_reclaim_thread(void) |
| 237 | { |
| 238 | int ret; |
| 239 | void *tret; |
| 240 | |
| 241 | STORE_SHARED(exit_reclaim, 1); |
| 242 | ret = pthread_join(tid_reclaim, &tret); |
| 243 | assert(!ret); |
| 244 | } |
| 245 | |
| 246 | void rcu_reclaim_register_thread(void) |
| 247 | { |
| 248 | int readers; |
| 249 | |
| 250 | internal_urcu_lock(&reclaim_thread_mutex); |
| 251 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 252 | /* In case gcc does not support constructor attribute */ |
| 253 | urcu_reclaim_init(); |
| 254 | reclaim_queue.q = malloc(sizeof(void *) * RECLAIM_QUEUE_SIZE); |
| 255 | rcu_add_reader(pthread_self()); |
| 256 | readers = num_readers; |
| 257 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 258 | |
| 259 | if (readers == 1) |
| 260 | start_reclaim_thread(); |
| 261 | internal_urcu_unlock(&reclaim_thread_mutex); |
| 262 | } |
| 263 | |
| 264 | void rcu_reclaim_unregister_thread(void) |
| 265 | { |
| 266 | int readers; |
| 267 | |
| 268 | internal_urcu_lock(&reclaim_thread_mutex); |
| 269 | internal_urcu_lock(&urcu_reclaim_mutex); |
| 270 | rcu_remove_reader(pthread_self()); |
| 271 | _rcu_reclaim_barrier_thread(); |
| 272 | free(reclaim_queue.q); |
| 273 | reclaim_queue.q = NULL; |
| 274 | readers = num_readers; |
| 275 | internal_urcu_unlock(&urcu_reclaim_mutex); |
| 276 | |
| 277 | if (readers == 0) |
| 278 | stop_reclaim_thread(); |
| 279 | internal_urcu_unlock(&reclaim_thread_mutex); |
| 280 | } |
| 281 | |
| 282 | /* |
| 283 | * urcu_init constructor. Called when the library is linked, but also when |
| 284 | * reader threads are calling rcu_register_thread(). Should only be called by a |
| 285 | * single thread at a given time. This is ensured by holing the |
| 286 | * internal_urcu_lock(&urcu_reclaim_mutex) from rcu_register_thread() or by |
| 287 | * running at library load time, which should not be executed by multiple |
| 288 | * threads nor concurrently with rcu_register_thread() anyway. |
| 289 | */ |
| 290 | void urcu_reclaim_init(void) |
| 291 | { |
| 292 | if (init_done) |
| 293 | return; |
| 294 | init_done = 1; |
| 295 | } |
| 296 | |
| 297 | void urcu_reclaim_exit(void) |
| 298 | { |
| 299 | free(registry); |
| 300 | } |