add sync_core primitive
[urcu.git] / urcu.c
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
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6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
7 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
b257a10b 8 *
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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
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22 *
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
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24 */
25
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26#include <stdio.h>
27#include <pthread.h>
28#include <signal.h>
29#include <assert.h>
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30#include <stdlib.h>
31#include <string.h>
09a9f986 32#include <errno.h>
e8043c1b 33#include <poll.h>
27b012e2 34
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35#include "urcu-static.h"
36/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
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37#include "urcu.h"
38
39pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
40
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41/*
42 * Global grace period counter.
43 * Contains the current RCU_GP_CTR_BIT.
44 * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
b0d5e790 45 * Written to only by writer with mutex taken. Read by both writer and readers.
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46 */
47long urcu_gp_ctr = RCU_GP_COUNT;
27b012e2 48
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49/*
50 * Written to only by each individual reader. Read by both the reader and the
51 * writers.
52 */
6e8b8429 53long __thread urcu_active_readers;
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54
55/* Thread IDs of registered readers */
56#define INIT_NUM_THREADS 4
57
0a52082b 58struct reader_registry {
27b012e2 59 pthread_t tid;
128166c9 60 long *urcu_active_readers;
09a9f986 61 char *need_mb;
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62};
63
cf380c2f 64#ifdef DEBUG_YIELD
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65unsigned int yield_active;
66unsigned int __thread rand_yield;
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67#endif
68
0a52082b 69static struct reader_registry *registry;
09a9f986 70static char __thread need_mb;
27b012e2 71static int num_readers, alloc_readers;
27b012e2 72
c265818b 73void internal_urcu_lock(void)
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74{
75 int ret;
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76
77#ifndef DISTRUST_SIGNALS_EXTREME
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78 ret = pthread_mutex_lock(&urcu_mutex);
79 if (ret) {
80 perror("Error in pthread mutex lock");
81 exit(-1);
82 }
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83#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
84 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
85 if (ret != EBUSY && ret != EINTR) {
86 printf("ret = %d, errno = %d\n", ret, errno);
87 perror("Error in pthread mutex lock");
88 exit(-1);
89 }
90 if (need_mb) {
91 smp_mb();
92 need_mb = 0;
93 smp_mb();
94 }
95 poll(NULL,0,10);
96 }
97#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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98}
99
c265818b 100void internal_urcu_unlock(void)
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101{
102 int ret;
103
104 ret = pthread_mutex_unlock(&urcu_mutex);
105 if (ret) {
106 perror("Error in pthread mutex unlock");
107 exit(-1);
108 }
109}
110
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111/*
112 * called with urcu_mutex held.
113 */
1430ee0b 114static void switch_next_urcu_qparity(void)
27b012e2 115{
b0d5e790 116 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
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117}
118
bb488185 119#ifdef DEBUG_FULL_MB
e8043c1b 120#ifdef HAS_INCOHERENT_CACHES
09a9f986 121static void force_mb_single_thread(struct reader_registry *index)
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122{
123 smp_mb();
124}
e8043c1b 125#endif /* #ifdef HAS_INCOHERENT_CACHES */
40e140c9 126
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127static void force_mb_all_threads(void)
128{
b715b99e 129 smp_mb();
bb488185 130}
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131#else /* #ifdef DEBUG_FULL_MB */
132#ifdef HAS_INCOHERENT_CACHES
09a9f986 133static void force_mb_single_thread(struct reader_registry *index)
40e140c9 134{
0a52082b 135 assert(registry);
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136 /*
137 * pthread_kill has a smp_mb(). But beware, we assume it performs
138 * a cache flush on architectures with non-coherent cache. Let's play
139 * safe and don't assume anything : we use smp_mc() to make sure the
140 * cache flush is enforced.
157dca95 141 */
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142 *index->need_mb = 1;
143 smp_mc(); /* write ->need_mb before sending the signals */
144 pthread_kill(index->tid, SIGURCU);
145 smp_mb();
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146 /*
147 * Wait for sighandler (and thus mb()) to execute on every thread.
148 * BUSY-LOOP.
149 */
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150 while (*index->need_mb) {
151 poll(NULL, 0, 1);
152 }
153 smp_mb(); /* read ->need_mb before ending the barrier */
40e140c9 154}
e8043c1b 155#endif /* #ifdef HAS_INCOHERENT_CACHES */
40e140c9 156
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157static void force_mb_all_threads(void)
158{
0a52082b 159 struct reader_registry *index;
27b012e2 160 /*
b715b99e 161 * Ask for each threads to execute a smp_mb() so we can consider the
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162 * compiler barriers around rcu read lock as real memory barriers.
163 */
0a52082b 164 if (!registry)
27b012e2 165 return;
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166 /*
167 * pthread_kill has a smp_mb(). But beware, we assume it performs
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168 * a cache flush on architectures with non-coherent cache. Let's play
169 * safe and don't assume anything : we use smp_mc() to make sure the
170 * cache flush is enforced.
3a86deba 171 */
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172 for (index = registry; index < registry + num_readers; index++) {
173 *index->need_mb = 1;
174 smp_mc(); /* write need_mb before sending the signal */
f69f195a 175 pthread_kill(index->tid, SIGURCU);
09a9f986 176 }
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177 /*
178 * Wait for sighandler (and thus mb()) to execute on every thread.
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179 *
180 * Note that the pthread_kill() will never be executed on systems
181 * that correctly deliver signals in a timely manner. However, it
182 * is not uncommon for kernels to have bugs that can result in
183 * lost or unduly delayed signals.
184 *
185 * If you are seeing the below pthread_kill() executing much at
186 * all, we suggest testing the underlying kernel and filing the
187 * relevant bug report. For Linux kernels, we recommend getting
188 * the Linux Test Project (LTP).
27b012e2 189 */
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190 for (index = registry; index < registry + num_readers; index++) {
191 while (*index->need_mb) {
192 pthread_kill(index->tid, SIGURCU);
193 poll(NULL, 0, 1);
194 }
195 }
196 smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 197}
e8043c1b 198#endif /* #else #ifdef DEBUG_FULL_MB */
27b012e2 199
1430ee0b 200void wait_for_quiescent_state(void)
27b012e2 201{
0a52082b 202 struct reader_registry *index;
27b012e2 203
0a52082b 204 if (!registry)
27b012e2 205 return;
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206 /*
207 * Wait for each thread urcu_active_readers count to become 0.
27b012e2 208 */
0a52082b 209 for (index = registry; index < registry + num_readers; index++) {
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210#ifndef HAS_INCOHERENT_CACHES
211 while (rcu_old_gp_ongoing(index->urcu_active_readers))
212 cpu_relax();
213#else /* #ifndef HAS_INCOHERENT_CACHES */
40e140c9 214 int wait_loops = 0;
27b012e2 215 /*
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216 * BUSY-LOOP. Force the reader thread to commit its
217 * urcu_active_readers update to memory if we wait for too long.
27b012e2 218 */
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219 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
220 if (wait_loops++ == KICK_READER_LOOPS) {
09a9f986 221 force_mb_single_thread(index);
40e140c9 222 wait_loops = 0;
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223 } else {
224 cpu_relax();
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225 }
226 }
e8043c1b 227#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 228 }
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229}
230
9598a481 231void synchronize_rcu(void)
2bc59bd7 232{
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233 internal_urcu_lock();
234
9598a481 235 /* All threads should read qparity before accessing data structure
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236 * where new ptr points to. Must be done within internal_urcu_lock
237 * because it iterates on reader threads.*/
9598a481 238 /* Write new ptr before changing the qparity */
2bc59bd7 239 force_mb_all_threads();
9598a481 240
9598a481 241 switch_next_urcu_qparity(); /* 0 -> 1 */
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242
243 /*
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244 * Must commit qparity update to memory before waiting for parity
245 * 0 quiescent state. Failure to do so could result in the writer
246 * waiting forever while new readers are always accessing data (no
247 * progress).
b0d5e790 248 * Ensured by STORE_SHARED and LOAD_SHARED.
2bc59bd7 249 */
2bc59bd7 250
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251 /*
252 * Wait for previous parity to be empty of readers.
253 */
254 wait_for_quiescent_state(); /* Wait readers in parity 0 */
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255
256 /*
257 * Must finish waiting for quiescent state for parity 0 before
258 * committing qparity update to memory. Failure to do so could result in
259 * the writer waiting forever while new readers are always accessing
260 * data (no progress).
b0d5e790 261 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 262 */
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263
264 switch_next_urcu_qparity(); /* 1 -> 0 */
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265
266 /*
267 * Must commit qparity update to memory before waiting for parity
268 * 1 quiescent state. Failure to do so could result in the writer
269 * waiting forever while new readers are always accessing data (no
270 * progress).
b0d5e790 271 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 272 */
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273
274 /*
275 * Wait for previous parity to be empty of readers.
276 */
277 wait_for_quiescent_state(); /* Wait readers in parity 1 */
9598a481 278
9598a481 279 /* Finish waiting for reader threads before letting the old ptr being
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280 * freed. Must be done within internal_urcu_lock because it iterates on
281 * reader threads. */
9598a481 282 force_mb_all_threads();
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283
284 internal_urcu_unlock();
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285}
286
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287/*
288 * library wrappers to be used by non-LGPL compatible source code.
289 */
290
291void rcu_read_lock(void)
292{
293 _rcu_read_lock();
294}
295
296void rcu_read_unlock(void)
297{
298 _rcu_read_unlock();
299}
300
301void *rcu_dereference(void *p)
302{
303 return _rcu_dereference(p);
304}
305
306void *rcu_assign_pointer_sym(void **p, void *v)
307{
308 wmb();
309 return STORE_SHARED(p, v);
310}
311
312void *rcu_xchg_pointer_sym(void **p, void *v)
313{
314 wmb();
315 return xchg(p, v);
316}
317
318void *rcu_publish_content_sym(void **p, void *v)
319{
320 void *oldptr;
321
322 oldptr = _rcu_xchg_pointer(p, v);
323 synchronize_rcu();
324 return oldptr;
325}
326
327static void rcu_add_reader(pthread_t id)
27b012e2 328{
0a52082b 329 struct reader_registry *oldarray;
f69f195a 330
0a52082b 331 if (!registry) {
27b012e2 332 alloc_readers = INIT_NUM_THREADS;
f69f195a 333 num_readers = 0;
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334 registry =
335 malloc(sizeof(struct reader_registry) * alloc_readers);
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336 }
337 if (alloc_readers < num_readers + 1) {
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338 oldarray = registry;
339 registry = malloc(sizeof(struct reader_registry)
27b012e2 340 * (alloc_readers << 1));
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341 memcpy(registry, oldarray,
342 sizeof(struct reader_registry) * alloc_readers);
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343 alloc_readers <<= 1;
344 free(oldarray);
345 }
0a52082b 346 registry[num_readers].tid = id;
27b012e2 347 /* reference to the TLS of _this_ reader thread. */
0a52082b 348 registry[num_readers].urcu_active_readers = &urcu_active_readers;
09a9f986 349 registry[num_readers].need_mb = &need_mb;
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350 num_readers++;
351}
352
353/*
354 * Never shrink (implementation limitation).
355 * This is O(nb threads). Eventually use a hash table.
356 */
121a5d44 357static void rcu_remove_reader(pthread_t id)
27b012e2 358{
0a52082b 359 struct reader_registry *index;
27b012e2 360
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361 assert(registry != NULL);
362 for (index = registry; index < registry + num_readers; index++) {
e6d6e2dc 363 if (pthread_equal(index->tid, id)) {
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364 memcpy(index, &registry[num_readers - 1],
365 sizeof(struct reader_registry));
366 registry[num_readers - 1].tid = 0;
367 registry[num_readers - 1].urcu_active_readers = NULL;
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368 num_readers--;
369 return;
370 }
371 }
372 /* Hrm not found, forgot to register ? */
373 assert(0);
374}
375
121a5d44 376void rcu_register_thread(void)
27b012e2 377{
c265818b 378 internal_urcu_lock();
121a5d44 379 rcu_add_reader(pthread_self());
c265818b 380 internal_urcu_unlock();
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381}
382
121a5d44 383void rcu_unregister_thread(void)
27b012e2 384{
c265818b 385 internal_urcu_lock();
121a5d44 386 rcu_remove_reader(pthread_self());
c265818b 387 internal_urcu_unlock();
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388}
389
bb488185 390#ifndef DEBUG_FULL_MB
121a5d44 391static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 392{
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393 /*
394 * Executing this smp_mb() is the only purpose of this signal handler.
395 * It punctually promotes barrier() into smp_mb() on every thread it is
396 * executed on.
397 */
b715b99e 398 smp_mb();
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399 need_mb = 0;
400 smp_mb();
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401}
402
403void __attribute__((constructor)) urcu_init(void)
404{
405 struct sigaction act;
406 int ret;
407
408 act.sa_sigaction = sigurcu_handler;
409 ret = sigaction(SIGURCU, &act, NULL);
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410 if (ret) {
411 perror("Error in sigaction");
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412 exit(-1);
413 }
414}
415
416void __attribute__((destructor)) urcu_exit(void)
417{
418 struct sigaction act;
419 int ret;
420
421 ret = sigaction(SIGURCU, NULL, &act);
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422 if (ret) {
423 perror("Error in sigaction");
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424 exit(-1);
425 }
426 assert(act.sa_sigaction == sigurcu_handler);
0a52082b 427 free(registry);
27b012e2 428}
e8043c1b 429#endif /* #ifndef DEBUG_FULL_MB */
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