Add missing rcu_cmpxchg_pointer define
[urcu.git] / urcu.c
CommitLineData
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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
0a1d290b 39#ifndef URCU_MB
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40static int init_done;
41
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42void __attribute__((constructor)) urcu_init(void);
43void __attribute__((destructor)) urcu_exit(void);
e90a6e9c 44#else
538d7df5 45void urcu_init(void)
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46{
47}
48#endif
8a5fb4c9 49
81d1f1f5 50static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
27b012e2 51
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52int gp_futex;
53
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54/*
55 * Global grace period counter.
56 * Contains the current RCU_GP_CTR_BIT.
afb8f2c9 57 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
b0d5e790 58 * Written to only by writer with mutex taken. Read by both writer and readers.
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59 */
60long urcu_gp_ctr = RCU_GP_COUNT;
27b012e2 61
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62/*
63 * Written to only by each individual reader. Read by both the reader and the
64 * writers.
65 */
6e8b8429 66long __thread urcu_active_readers;
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67
68/* Thread IDs of registered readers */
69#define INIT_NUM_THREADS 4
70
0a52082b 71struct reader_registry {
27b012e2 72 pthread_t tid;
128166c9 73 long *urcu_active_readers;
09a9f986 74 char *need_mb;
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75};
76
cf380c2f 77#ifdef DEBUG_YIELD
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78unsigned int yield_active;
79unsigned int __thread rand_yield;
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80#endif
81
0a52082b 82static struct reader_registry *registry;
09a9f986 83static char __thread need_mb;
27b012e2 84static int num_readers, alloc_readers;
27b012e2 85
81d1f1f5 86static void internal_urcu_lock(void)
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87{
88 int ret;
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89
90#ifndef DISTRUST_SIGNALS_EXTREME
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91 ret = pthread_mutex_lock(&urcu_mutex);
92 if (ret) {
93 perror("Error in pthread mutex lock");
94 exit(-1);
95 }
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96#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
97 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
98 if (ret != EBUSY && ret != EINTR) {
99 printf("ret = %d, errno = %d\n", ret, errno);
100 perror("Error in pthread mutex lock");
101 exit(-1);
102 }
103 if (need_mb) {
104 smp_mb();
105 need_mb = 0;
106 smp_mb();
107 }
108 poll(NULL,0,10);
109 }
110#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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111}
112
81d1f1f5 113static void internal_urcu_unlock(void)
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114{
115 int ret;
116
117 ret = pthread_mutex_unlock(&urcu_mutex);
118 if (ret) {
119 perror("Error in pthread mutex unlock");
120 exit(-1);
121 }
122}
123
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124/*
125 * called with urcu_mutex held.
126 */
1430ee0b 127static void switch_next_urcu_qparity(void)
27b012e2 128{
b0d5e790 129 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
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130}
131
0a1d290b 132#ifdef URCU_MB
09a9f986 133static void force_mb_single_thread(struct reader_registry *index)
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134{
135 smp_mb();
136}
137
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138static void force_mb_all_threads(void)
139{
b715b99e 140 smp_mb();
bb488185 141}
0a1d290b 142#else /* #ifdef URCU_MB */
09a9f986 143static void force_mb_single_thread(struct reader_registry *index)
40e140c9 144{
0a52082b 145 assert(registry);
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146 /*
147 * pthread_kill has a smp_mb(). But beware, we assume it performs
148 * a cache flush on architectures with non-coherent cache. Let's play
149 * safe and don't assume anything : we use smp_mc() to make sure the
150 * cache flush is enforced.
157dca95 151 */
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152 *index->need_mb = 1;
153 smp_mc(); /* write ->need_mb before sending the signals */
154 pthread_kill(index->tid, SIGURCU);
155 smp_mb();
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156 /*
157 * Wait for sighandler (and thus mb()) to execute on every thread.
158 * BUSY-LOOP.
159 */
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160 while (*index->need_mb) {
161 poll(NULL, 0, 1);
162 }
163 smp_mb(); /* read ->need_mb before ending the barrier */
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164}
165
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166static void force_mb_all_threads(void)
167{
0a52082b 168 struct reader_registry *index;
27b012e2 169 /*
b715b99e 170 * Ask for each threads to execute a smp_mb() so we can consider the
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171 * compiler barriers around rcu read lock as real memory barriers.
172 */
0a52082b 173 if (!registry)
27b012e2 174 return;
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175 /*
176 * pthread_kill has a smp_mb(). But beware, we assume it performs
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177 * a cache flush on architectures with non-coherent cache. Let's play
178 * safe and don't assume anything : we use smp_mc() to make sure the
179 * cache flush is enforced.
3a86deba 180 */
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181 for (index = registry; index < registry + num_readers; index++) {
182 *index->need_mb = 1;
183 smp_mc(); /* write need_mb before sending the signal */
f69f195a 184 pthread_kill(index->tid, SIGURCU);
09a9f986 185 }
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186 /*
187 * Wait for sighandler (and thus mb()) to execute on every thread.
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188 *
189 * Note that the pthread_kill() will never be executed on systems
190 * that correctly deliver signals in a timely manner. However, it
191 * is not uncommon for kernels to have bugs that can result in
192 * lost or unduly delayed signals.
193 *
194 * If you are seeing the below pthread_kill() executing much at
195 * all, we suggest testing the underlying kernel and filing the
196 * relevant bug report. For Linux kernels, we recommend getting
197 * the Linux Test Project (LTP).
27b012e2 198 */
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199 for (index = registry; index < registry + num_readers; index++) {
200 while (*index->need_mb) {
201 pthread_kill(index->tid, SIGURCU);
202 poll(NULL, 0, 1);
203 }
204 }
205 smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 206}
0a1d290b 207#endif /* #else #ifdef URCU_MB */
27b012e2 208
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209/*
210 * synchronize_rcu() waiting. Single thread.
211 */
212static void wait_gp(struct reader_registry *index)
213{
214 atomic_dec(&gp_futex);
215 force_mb_single_thread(index); /* Write futex before read reader_gp */
216 if (!rcu_old_gp_ongoing(index->urcu_active_readers)) {
217 /* Read reader_gp before write futex */
218 force_mb_single_thread(index);
219 /* Callbacks are queued, don't wait. */
220 atomic_set(&gp_futex, 0);
221 } else {
222 /* Read reader_gp before read futex */
223 force_mb_single_thread(index);
224 if (atomic_read(&gp_futex) == -1)
225 futex(&gp_futex, FUTEX_WAIT, -1,
226 NULL, NULL, 0);
227 }
228}
229
1430ee0b 230void wait_for_quiescent_state(void)
27b012e2 231{
0a52082b 232 struct reader_registry *index;
27b012e2 233
0a52082b 234 if (!registry)
27b012e2 235 return;
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236 /*
237 * Wait for each thread urcu_active_readers count to become 0.
27b012e2 238 */
0a52082b 239 for (index = registry; index < registry + num_readers; index++) {
bc6c15bb 240 int wait_loops = 0;
e8043c1b 241#ifndef HAS_INCOHERENT_CACHES
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242 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
243 if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
244 wait_gp(index);
245 } else {
246 cpu_relax();
247 }
248 }
e8043c1b 249#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 250 /*
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251 * BUSY-LOOP. Force the reader thread to commit its
252 * urcu_active_readers update to memory if we wait for too long.
27b012e2 253 */
40e140c9 254 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
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255 switch (wait_loops++) {
256 case RCU_QS_ACTIVE_ATTEMPTS:
257 wait_gp(index);
258 break;
259 case KICK_READER_LOOPS:
09a9f986 260 force_mb_single_thread(index);
40e140c9 261 wait_loops = 0;
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262 break;
263 default:
3b55dbf4 264 cpu_relax();
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265 }
266 }
e8043c1b 267#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 268 }
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269}
270
9598a481 271void synchronize_rcu(void)
2bc59bd7 272{
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273 internal_urcu_lock();
274
9598a481 275 /* All threads should read qparity before accessing data structure
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276 * where new ptr points to. Must be done within internal_urcu_lock
277 * because it iterates on reader threads.*/
9598a481 278 /* Write new ptr before changing the qparity */
2bc59bd7 279 force_mb_all_threads();
9598a481 280
9598a481 281 switch_next_urcu_qparity(); /* 0 -> 1 */
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282
283 /*
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284 * Must commit qparity update to memory before waiting for parity
285 * 0 quiescent state. Failure to do so could result in the writer
286 * waiting forever while new readers are always accessing data (no
287 * progress).
b0d5e790 288 * Ensured by STORE_SHARED and LOAD_SHARED.
2bc59bd7 289 */
2bc59bd7 290
67c2d80b 291 /*
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292 * Adding a smp_mb() which is _not_ formally required, but makes the
293 * model easier to understand. It does not have a big performance impact
294 * anyway, given this is the write-side.
67c2d80b 295 */
5dba80f9 296 smp_mb();
67c2d80b 297
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298 /*
299 * Wait for previous parity to be empty of readers.
300 */
301 wait_for_quiescent_state(); /* Wait readers in parity 0 */
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302
303 /*
304 * Must finish waiting for quiescent state for parity 0 before
305 * committing qparity update to memory. Failure to do so could result in
306 * the writer waiting forever while new readers are always accessing
307 * data (no progress).
b0d5e790 308 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 309 */
9598a481 310
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311 /*
312 * Adding a smp_mb() which is _not_ formally required, but makes the
313 * model easier to understand. It does not have a big performance impact
314 * anyway, given this is the write-side.
315 */
316 smp_mb();
67c2d80b 317
9598a481 318 switch_next_urcu_qparity(); /* 1 -> 0 */
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319
320 /*
321 * Must commit qparity update to memory before waiting for parity
322 * 1 quiescent state. Failure to do so could result in the writer
323 * waiting forever while new readers are always accessing data (no
324 * progress).
b0d5e790 325 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 326 */
9598a481 327
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328 /*
329 * Adding a smp_mb() which is _not_ formally required, but makes the
330 * model easier to understand. It does not have a big performance impact
331 * anyway, given this is the write-side.
332 */
333 smp_mb();
67c2d80b 334
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335 /*
336 * Wait for previous parity to be empty of readers.
337 */
338 wait_for_quiescent_state(); /* Wait readers in parity 1 */
9598a481 339
9598a481 340 /* Finish waiting for reader threads before letting the old ptr being
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341 * freed. Must be done within internal_urcu_lock because it iterates on
342 * reader threads. */
9598a481 343 force_mb_all_threads();
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344
345 internal_urcu_unlock();
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346}
347
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348/*
349 * library wrappers to be used by non-LGPL compatible source code.
350 */
351
352void rcu_read_lock(void)
353{
354 _rcu_read_lock();
355}
356
357void rcu_read_unlock(void)
358{
359 _rcu_read_unlock();
360}
361
362void *rcu_dereference(void *p)
363{
364 return _rcu_dereference(p);
365}
366
367void *rcu_assign_pointer_sym(void **p, void *v)
368{
369 wmb();
370 return STORE_SHARED(p, v);
371}
372
373void *rcu_xchg_pointer_sym(void **p, void *v)
374{
375 wmb();
376 return xchg(p, v);
377}
378
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379void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
380{
381 wmb();
382 return cmpxchg(p, old, _new);
383}
384
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385void *rcu_publish_content_sym(void **p, void *v)
386{
387 void *oldptr;
388
389 oldptr = _rcu_xchg_pointer(p, v);
390 synchronize_rcu();
391 return oldptr;
392}
393
394static void rcu_add_reader(pthread_t id)
27b012e2 395{
0a52082b 396 struct reader_registry *oldarray;
f69f195a 397
0a52082b 398 if (!registry) {
27b012e2 399 alloc_readers = INIT_NUM_THREADS;
f69f195a 400 num_readers = 0;
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401 registry =
402 malloc(sizeof(struct reader_registry) * alloc_readers);
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403 }
404 if (alloc_readers < num_readers + 1) {
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405 oldarray = registry;
406 registry = malloc(sizeof(struct reader_registry)
27b012e2 407 * (alloc_readers << 1));
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408 memcpy(registry, oldarray,
409 sizeof(struct reader_registry) * alloc_readers);
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410 alloc_readers <<= 1;
411 free(oldarray);
412 }
0a52082b 413 registry[num_readers].tid = id;
27b012e2 414 /* reference to the TLS of _this_ reader thread. */
0a52082b 415 registry[num_readers].urcu_active_readers = &urcu_active_readers;
09a9f986 416 registry[num_readers].need_mb = &need_mb;
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417 num_readers++;
418}
419
420/*
421 * Never shrink (implementation limitation).
422 * This is O(nb threads). Eventually use a hash table.
423 */
121a5d44 424static void rcu_remove_reader(pthread_t id)
27b012e2 425{
0a52082b 426 struct reader_registry *index;
27b012e2 427
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428 assert(registry != NULL);
429 for (index = registry; index < registry + num_readers; index++) {
e6d6e2dc 430 if (pthread_equal(index->tid, id)) {
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431 memcpy(index, &registry[num_readers - 1],
432 sizeof(struct reader_registry));
433 registry[num_readers - 1].tid = 0;
434 registry[num_readers - 1].urcu_active_readers = NULL;
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435 num_readers--;
436 return;
437 }
438 }
439 /* Hrm not found, forgot to register ? */
440 assert(0);
441}
442
121a5d44 443void rcu_register_thread(void)
27b012e2 444{
c265818b 445 internal_urcu_lock();
8a5fb4c9 446 urcu_init(); /* In case gcc does not support constructor attribute */
121a5d44 447 rcu_add_reader(pthread_self());
c265818b 448 internal_urcu_unlock();
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449}
450
121a5d44 451void rcu_unregister_thread(void)
27b012e2 452{
c265818b 453 internal_urcu_lock();
121a5d44 454 rcu_remove_reader(pthread_self());
c265818b 455 internal_urcu_unlock();
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456}
457
0a1d290b 458#ifndef URCU_MB
121a5d44 459static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 460{
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461 /*
462 * Executing this smp_mb() is the only purpose of this signal handler.
463 * It punctually promotes barrier() into smp_mb() on every thread it is
464 * executed on.
465 */
b715b99e 466 smp_mb();
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467 need_mb = 0;
468 smp_mb();
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469}
470
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471/*
472 * urcu_init constructor. Called when the library is linked, but also when
473 * reader threads are calling rcu_register_thread().
474 * Should only be called by a single thread at a given time. This is ensured by
475 * holing the internal_urcu_lock() from rcu_register_thread() or by running at
476 * library load time, which should not be executed by multiple threads nor
477 * concurrently with rcu_register_thread() anyway.
478 */
479void urcu_init(void)
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480{
481 struct sigaction act;
482 int ret;
483
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484 if (init_done)
485 return;
486 init_done = 1;
487
27b012e2 488 act.sa_sigaction = sigurcu_handler;
dd052bd3 489 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 490 sigemptyset(&act.sa_mask);
27b012e2 491 ret = sigaction(SIGURCU, &act, NULL);
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492 if (ret) {
493 perror("Error in sigaction");
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494 exit(-1);
495 }
496}
497
8a5fb4c9 498void urcu_exit(void)
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499{
500 struct sigaction act;
501 int ret;
502
503 ret = sigaction(SIGURCU, NULL, &act);
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504 if (ret) {
505 perror("Error in sigaction");
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506 exit(-1);
507 }
508 assert(act.sa_sigaction == sigurcu_handler);
0a52082b 509 free(registry);
27b012e2 510}
0a1d290b 511#endif /* #ifndef URCU_MB */
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