| 1 | /* |
| 2 | * urcu-qsbr.c |
| 3 | * |
| 4 | * Userspace RCU QSBR library |
| 5 | * |
| 6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> |
| 7 | * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. |
| 8 | * |
| 9 | * This library is free software; you can redistribute it and/or |
| 10 | * modify it under the terms of the GNU Lesser General Public |
| 11 | * License as published by the Free Software Foundation; either |
| 12 | * version 2.1 of the License, or (at your option) any later version. |
| 13 | * |
| 14 | * This library is distributed in the hope that it will be useful, |
| 15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 17 | * Lesser General Public License for more details. |
| 18 | * |
| 19 | * You should have received a copy of the GNU Lesser General Public |
| 20 | * License along with this library; if not, write to the Free Software |
| 21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 22 | * |
| 23 | * IBM's contributions to this file may be relicensed under LGPLv2 or later. |
| 24 | */ |
| 25 | |
| 26 | #include <stdio.h> |
| 27 | #include <pthread.h> |
| 28 | #include <signal.h> |
| 29 | #include <assert.h> |
| 30 | #include <stdlib.h> |
| 31 | #include <string.h> |
| 32 | #include <errno.h> |
| 33 | #include <poll.h> |
| 34 | |
| 35 | #include "urcu-qsbr-static.h" |
| 36 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
| 37 | #include "urcu-qsbr.h" |
| 38 | |
| 39 | pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; |
| 40 | |
| 41 | /* |
| 42 | * Global grace period counter. |
| 43 | */ |
| 44 | long urcu_gp_ctr = 0; |
| 45 | |
| 46 | /* |
| 47 | * Written to only by each individual reader. Read by both the reader and the |
| 48 | * writers. |
| 49 | */ |
| 50 | long __thread rcu_reader_qs_gp; |
| 51 | |
| 52 | /* Thread IDs of registered readers */ |
| 53 | #define INIT_NUM_THREADS 4 |
| 54 | |
| 55 | struct reader_registry { |
| 56 | pthread_t tid; |
| 57 | long *rcu_reader_qs_gp; |
| 58 | }; |
| 59 | |
| 60 | #ifdef DEBUG_YIELD |
| 61 | unsigned int yield_active; |
| 62 | unsigned int __thread rand_yield; |
| 63 | #endif |
| 64 | |
| 65 | static struct reader_registry *registry; |
| 66 | static int num_readers, alloc_readers; |
| 67 | |
| 68 | static void internal_urcu_lock(void) |
| 69 | { |
| 70 | int ret; |
| 71 | |
| 72 | #ifndef DISTRUST_SIGNALS_EXTREME |
| 73 | ret = pthread_mutex_lock(&urcu_mutex); |
| 74 | if (ret) { |
| 75 | perror("Error in pthread mutex lock"); |
| 76 | exit(-1); |
| 77 | } |
| 78 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
| 79 | while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { |
| 80 | if (ret != EBUSY && ret != EINTR) { |
| 81 | printf("ret = %d, errno = %d\n", ret, errno); |
| 82 | perror("Error in pthread mutex lock"); |
| 83 | exit(-1); |
| 84 | } |
| 85 | poll(NULL,0,10); |
| 86 | } |
| 87 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ |
| 88 | } |
| 89 | |
| 90 | static void internal_urcu_unlock(void) |
| 91 | { |
| 92 | int ret; |
| 93 | |
| 94 | ret = pthread_mutex_unlock(&urcu_mutex); |
| 95 | if (ret) { |
| 96 | perror("Error in pthread mutex unlock"); |
| 97 | exit(-1); |
| 98 | } |
| 99 | } |
| 100 | |
| 101 | #ifdef HAS_INCOHERENT_CACHES |
| 102 | static void force_mb_single_thread(struct reader_registry *index) |
| 103 | { |
| 104 | smp_mb(); |
| 105 | } |
| 106 | #endif /* #ifdef HAS_INCOHERENT_CACHES */ |
| 107 | |
| 108 | static void force_mb_all_threads(void) |
| 109 | { |
| 110 | smp_mb(); |
| 111 | } |
| 112 | |
| 113 | static void wait_for_quiescent_state(void) |
| 114 | { |
| 115 | struct reader_registry *index; |
| 116 | |
| 117 | if (!registry) |
| 118 | return; |
| 119 | /* |
| 120 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
| 121 | */ |
| 122 | for (index = registry; index < registry + num_readers; index++) { |
| 123 | #ifndef HAS_INCOHERENT_CACHES |
| 124 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
| 125 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) |
| 126 | cpu_relax(); |
| 127 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
| 128 | int wait_loops = 0; |
| 129 | /* |
| 130 | * BUSY-LOOP. Force the reader thread to commit its |
| 131 | * rcu_reader_qs_gp update to memory if we wait for too long. |
| 132 | */ |
| 133 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
| 134 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { |
| 135 | if (wait_loops++ == KICK_READER_LOOPS) { |
| 136 | force_mb_single_thread(index); |
| 137 | wait_loops = 0; |
| 138 | } else { |
| 139 | cpu_relax(); |
| 140 | } |
| 141 | } |
| 142 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | void synchronize_rcu(void) |
| 147 | { |
| 148 | int was_online; |
| 149 | |
| 150 | was_online = rcu_reader_qs_gp & 1; |
| 151 | |
| 152 | /* |
| 153 | * Mark the writer thread offline to make sure we don't wait for |
| 154 | * our own quiescent state. This allows using synchronize_rcu() in |
| 155 | * threads registered as readers. |
| 156 | */ |
| 157 | if (was_online) |
| 158 | _rcu_thread_offline(); |
| 159 | |
| 160 | internal_urcu_lock(); |
| 161 | force_mb_all_threads(); |
| 162 | urcu_gp_ctr += 2; |
| 163 | wait_for_quiescent_state(); |
| 164 | force_mb_all_threads(); |
| 165 | internal_urcu_unlock(); |
| 166 | |
| 167 | if (was_online) |
| 168 | _rcu_thread_online(); |
| 169 | } |
| 170 | |
| 171 | /* |
| 172 | * library wrappers to be used by non-LGPL compatible source code. |
| 173 | */ |
| 174 | |
| 175 | void rcu_read_lock(void) |
| 176 | { |
| 177 | _rcu_read_lock(); |
| 178 | } |
| 179 | |
| 180 | void rcu_read_unlock(void) |
| 181 | { |
| 182 | _rcu_read_unlock(); |
| 183 | } |
| 184 | |
| 185 | void *rcu_dereference(void *p) |
| 186 | { |
| 187 | return _rcu_dereference(p); |
| 188 | } |
| 189 | |
| 190 | void *rcu_assign_pointer_sym(void **p, void *v) |
| 191 | { |
| 192 | wmb(); |
| 193 | return STORE_SHARED(p, v); |
| 194 | } |
| 195 | |
| 196 | void *rcu_xchg_pointer_sym(void **p, void *v) |
| 197 | { |
| 198 | wmb(); |
| 199 | return xchg(p, v); |
| 200 | } |
| 201 | |
| 202 | void *rcu_publish_content_sym(void **p, void *v) |
| 203 | { |
| 204 | void *oldptr; |
| 205 | |
| 206 | oldptr = _rcu_xchg_pointer(p, v); |
| 207 | synchronize_rcu(); |
| 208 | return oldptr; |
| 209 | } |
| 210 | |
| 211 | void rcu_quiescent_state(void) |
| 212 | { |
| 213 | _rcu_quiescent_state(); |
| 214 | } |
| 215 | |
| 216 | void rcu_thread_offline(void) |
| 217 | { |
| 218 | _rcu_thread_offline(); |
| 219 | } |
| 220 | |
| 221 | void rcu_thread_online(void) |
| 222 | { |
| 223 | _rcu_thread_online(); |
| 224 | } |
| 225 | |
| 226 | static void rcu_add_reader(pthread_t id) |
| 227 | { |
| 228 | struct reader_registry *oldarray; |
| 229 | |
| 230 | if (!registry) { |
| 231 | alloc_readers = INIT_NUM_THREADS; |
| 232 | num_readers = 0; |
| 233 | registry = |
| 234 | malloc(sizeof(struct reader_registry) * alloc_readers); |
| 235 | } |
| 236 | if (alloc_readers < num_readers + 1) { |
| 237 | oldarray = registry; |
| 238 | registry = malloc(sizeof(struct reader_registry) |
| 239 | * (alloc_readers << 1)); |
| 240 | memcpy(registry, oldarray, |
| 241 | sizeof(struct reader_registry) * alloc_readers); |
| 242 | alloc_readers <<= 1; |
| 243 | free(oldarray); |
| 244 | } |
| 245 | registry[num_readers].tid = id; |
| 246 | /* reference to the TLS of _this_ reader thread. */ |
| 247 | registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; |
| 248 | num_readers++; |
| 249 | } |
| 250 | |
| 251 | /* |
| 252 | * Never shrink (implementation limitation). |
| 253 | * This is O(nb threads). Eventually use a hash table. |
| 254 | */ |
| 255 | static void rcu_remove_reader(pthread_t id) |
| 256 | { |
| 257 | struct reader_registry *index; |
| 258 | |
| 259 | assert(registry != NULL); |
| 260 | for (index = registry; index < registry + num_readers; index++) { |
| 261 | if (pthread_equal(index->tid, id)) { |
| 262 | memcpy(index, ®istry[num_readers - 1], |
| 263 | sizeof(struct reader_registry)); |
| 264 | registry[num_readers - 1].tid = 0; |
| 265 | registry[num_readers - 1].rcu_reader_qs_gp = NULL; |
| 266 | num_readers--; |
| 267 | return; |
| 268 | } |
| 269 | } |
| 270 | /* Hrm not found, forgot to register ? */ |
| 271 | assert(0); |
| 272 | } |
| 273 | |
| 274 | void rcu_register_thread(void) |
| 275 | { |
| 276 | internal_urcu_lock(); |
| 277 | rcu_add_reader(pthread_self()); |
| 278 | internal_urcu_unlock(); |
| 279 | _rcu_thread_online(); |
| 280 | } |
| 281 | |
| 282 | void rcu_unregister_thread(void) |
| 283 | { |
| 284 | /* |
| 285 | * We have to make the thread offline otherwise we end up dealocking |
| 286 | * with a waiting writer. |
| 287 | */ |
| 288 | _rcu_thread_offline(); |
| 289 | internal_urcu_lock(); |
| 290 | rcu_remove_reader(pthread_self()); |
| 291 | internal_urcu_unlock(); |
| 292 | } |