Implement urcu/tls-compat.h
[urcu.git] / urcu.c
CommitLineData
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
6982d6d7 6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
af02d47e 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
fdf01eed 26#define _BSD_SOURCE
c1d2c60b 27#define _GNU_SOURCE
71c811bf 28#define _LGPL_SOURCE
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29#include <stdio.h>
30#include <pthread.h>
31#include <signal.h>
32#include <assert.h>
f69f195a 33#include <stdlib.h>
6d841bc2 34#include <stdint.h>
f69f195a 35#include <string.h>
09a9f986 36#include <errno.h>
e8043c1b 37#include <poll.h>
27b012e2 38
71c811bf 39#include "urcu/wfqueue.h"
57760d44 40#include "urcu/map/urcu.h"
af7c2dbe 41#include "urcu/static/urcu.h"
618b2595 42#include "urcu-pointer.h"
71c811bf 43
121a5d44 44/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf 45#undef _LGPL_SOURCE
27b012e2 46#include "urcu.h"
71c811bf 47#define _LGPL_SOURCE
27b012e2 48
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49/*
50 * If a reader is really non-cooperative and refuses to commit its
51 * rcu_active_readers count to memory (there is no barrier in the reader
52 * per-se), kick it after a few loops waiting for it.
53 */
54#define KICK_READER_LOOPS 10000
55
56/*
57 * Active attempts to check for reader Q.S. before calling futex().
58 */
59#define RCU_QS_ACTIVE_ATTEMPTS 100
60
fdf01eed 61#ifdef RCU_MEMBARRIER
834a45ba 62static int init_done;
fdf01eed 63int has_sys_membarrier;
834a45ba 64
02be5561 65void __attribute__((constructor)) rcu_init(void);
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66#endif
67
68#ifdef RCU_MB
02be5561 69void rcu_init(void)
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70{
71}
72#endif
8a5fb4c9 73
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74#ifdef RCU_SIGNAL
75static int init_done;
76
77void __attribute__((constructor)) rcu_init(void);
78void __attribute__((destructor)) rcu_exit(void);
79#endif
80
6abb4bd5 81static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
27b012e2 82
6d841bc2 83int32_t gp_futex;
bc6c15bb 84
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85/*
86 * Global grace period counter.
02be5561 87 * Contains the current RCU_GP_CTR_PHASE.
afb8f2c9 88 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
b0d5e790 89 * Written to only by writer with mutex taken. Read by both writer and readers.
128166c9 90 */
27d65bc5 91unsigned long rcu_gp_ctr = RCU_GP_COUNT;
27b012e2 92
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93/*
94 * Written to only by each individual reader. Read by both the reader and the
95 * writers.
96 */
02be5561 97struct rcu_reader __thread rcu_reader;
27b012e2 98
cf380c2f 99#ifdef DEBUG_YIELD
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100unsigned int yield_active;
101unsigned int __thread rand_yield;
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102#endif
103
16aa9ee8 104static CDS_LIST_HEAD(registry);
27b012e2 105
6abb4bd5 106static void mutex_lock(pthread_mutex_t *mutex)
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107{
108 int ret;
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109
110#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 111 ret = pthread_mutex_lock(mutex);
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112 if (ret) {
113 perror("Error in pthread mutex lock");
114 exit(-1);
115 }
09a9f986 116#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 117 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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118 if (ret != EBUSY && ret != EINTR) {
119 printf("ret = %d, errno = %d\n", ret, errno);
120 perror("Error in pthread mutex lock");
121 exit(-1);
122 }
6cf3827c 123 if (CMM_LOAD_SHARED(rcu_reader.need_mb)) {
5481ddb3 124 cmm_smp_mb();
6cf3827c 125 _CMM_STORE_SHARED(rcu_reader.need_mb, 0);
5481ddb3 126 cmm_smp_mb();
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127 }
128 poll(NULL,0,10);
129 }
130#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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131}
132
6abb4bd5 133static void mutex_unlock(pthread_mutex_t *mutex)
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134{
135 int ret;
136
6abb4bd5 137 ret = pthread_mutex_unlock(mutex);
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138 if (ret) {
139 perror("Error in pthread mutex unlock");
140 exit(-1);
141 }
142}
143
fdf01eed 144#ifdef RCU_MEMBARRIER
25cc6d18 145static void smp_mb_master(int group)
fdf01eed 146{
a0b7f7ea 147 if (caa_likely(has_sys_membarrier))
f0708810 148 membarrier(MEMBARRIER_EXPEDITED);
fdf01eed 149 else
5481ddb3 150 cmm_smp_mb();
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151}
152#endif
153
02be5561 154#ifdef RCU_MB
25cc6d18 155static void smp_mb_master(int group)
40e140c9 156{
5481ddb3 157 cmm_smp_mb();
40e140c9 158}
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159#endif
160
161#ifdef RCU_SIGNAL
78ff9419 162static void force_mb_all_readers(void)
27b012e2 163{
02be5561 164 struct rcu_reader *index;
e3b0cef0 165
27b012e2 166 /*
5481ddb3 167 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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168 * compiler barriers around rcu read lock as real memory barriers.
169 */
16aa9ee8 170 if (cds_list_empty(&registry))
27b012e2 171 return;
3a86deba 172 /*
5481ddb3 173 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 174 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 175 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 176 * cache flush is enforced.
3a86deba 177 */
16aa9ee8 178 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 179 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 180 pthread_kill(index->tid, SIGRCU);
09a9f986 181 }
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182 /*
183 * Wait for sighandler (and thus mb()) to execute on every thread.
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184 *
185 * Note that the pthread_kill() will never be executed on systems
186 * that correctly deliver signals in a timely manner. However, it
187 * is not uncommon for kernels to have bugs that can result in
188 * lost or unduly delayed signals.
189 *
190 * If you are seeing the below pthread_kill() executing much at
191 * all, we suggest testing the underlying kernel and filing the
192 * relevant bug report. For Linux kernels, we recommend getting
193 * the Linux Test Project (LTP).
27b012e2 194 */
16aa9ee8 195 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 196 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 197 pthread_kill(index->tid, SIGRCU);
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198 poll(NULL, 0, 1);
199 }
200 }
5481ddb3 201 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 202}
9d7e3f89 203
25cc6d18 204static void smp_mb_master(int group)
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205{
206 force_mb_all_readers();
207}
fdf01eed 208#endif /* #ifdef RCU_SIGNAL */
27b012e2 209
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210/*
211 * synchronize_rcu() waiting. Single thread.
212 */
cfe78e25 213static void wait_gp(void)
bc6c15bb 214{
cfe78e25 215 /* Read reader_gp before read futex */
25cc6d18 216 smp_mb_master(RCU_MB_GROUP);
cfe78e25 217 if (uatomic_read(&gp_futex) == -1)
0854ccff 218 futex_async(&gp_futex, FUTEX_WAIT, -1,
cfe78e25 219 NULL, NULL, 0);
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220}
221
2dfb8b5e 222void update_counter_and_wait(void)
27b012e2 223{
16aa9ee8 224 CDS_LIST_HEAD(qsreaders);
cfe78e25 225 int wait_loops = 0;
02be5561 226 struct rcu_reader *index, *tmp;
27b012e2 227
32c15e4e 228 /* Switch parity: 0 -> 1, 1 -> 0 */
6cf3827c 229 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
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230
231 /*
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232 * Must commit rcu_gp_ctr update to memory before waiting for quiescent
233 * state. Failure to do so could result in the writer waiting forever
234 * while new readers are always accessing data (no progress). Enforce
235 * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
2dfb8b5e 236 */
5481ddb3 237 cmm_barrier();
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238
239 /*
935b11ff 240 *
5481ddb3 241 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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242 * model easier to understand. It does not have a big performance impact
243 * anyway, given this is the write-side.
244 */
5481ddb3 245 cmm_smp_mb();
2dfb8b5e 246
40e140c9 247 /*
02be5561 248 * Wait for each thread rcu_reader.ctr count to become 0.
27b012e2 249 */
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250 for (;;) {
251 wait_loops++;
252 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
253 uatomic_dec(&gp_futex);
254 /* Write futex before read reader_gp */
25cc6d18 255 smp_mb_master(RCU_MB_GROUP);
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256 }
257
16aa9ee8 258 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
b95a001f 259 if (!rcu_gp_ongoing(&index->ctr))
16aa9ee8 260 cds_list_move(&index->node, &qsreaders);
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261 }
262
e8043c1b 263#ifndef HAS_INCOHERENT_CACHES
16aa9ee8 264 if (cds_list_empty(&registry)) {
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265 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
266 /* Read reader_gp before write futex */
25cc6d18 267 smp_mb_master(RCU_MB_GROUP);
cfe78e25 268 uatomic_set(&gp_futex, 0);
bc6c15bb 269 }
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270 break;
271 } else {
272 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
273 wait_gp();
274 else
06f22bdb 275 caa_cpu_relax();
bc6c15bb 276 }
e8043c1b 277#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 278 /*
40e140c9 279 * BUSY-LOOP. Force the reader thread to commit its
02be5561 280 * rcu_reader.ctr update to memory if we wait for too long.
27b012e2 281 */
16aa9ee8 282 if (cds_list_empty(&registry)) {
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283 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
284 /* Read reader_gp before write futex */
25cc6d18 285 smp_mb_master(RCU_MB_GROUP);
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286 uatomic_set(&gp_futex, 0);
287 }
288 break;
289 } else {
290 switch (wait_loops) {
bc6c15bb 291 case RCU_QS_ACTIVE_ATTEMPTS:
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292 wait_gp();
293 break; /* only escape switch */
bc6c15bb 294 case KICK_READER_LOOPS:
25cc6d18 295 smp_mb_master(RCU_MB_GROUP);
40e140c9 296 wait_loops = 0;
cfe78e25 297 break; /* only escape switch */
bc6c15bb 298 default:
06f22bdb 299 caa_cpu_relax();
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300 }
301 }
e8043c1b 302#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 303 }
cfe78e25 304 /* put back the reader list in the registry */
16aa9ee8 305 cds_list_splice(&qsreaders, &registry);
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306}
307
9598a481 308void synchronize_rcu(void)
2bc59bd7 309{
6abb4bd5 310 mutex_lock(&rcu_gp_lock);
135530fd 311
16aa9ee8 312 if (cds_list_empty(&registry))
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313 goto out;
314
9598a481 315 /* All threads should read qparity before accessing data structure
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316 * where new ptr points to. Must be done within rcu_gp_lock because it
317 * iterates on reader threads.*/
9598a481 318 /* Write new ptr before changing the qparity */
25cc6d18 319 smp_mb_master(RCU_MB_GROUP);
9598a481 320
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321 /*
322 * Wait for previous parity to be empty of readers.
323 */
2dfb8b5e 324 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
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325
326 /*
327 * Must finish waiting for quiescent state for parity 0 before
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328 * committing next rcu_gp_ctr update to memory. Failure to do so could
329 * result in the writer waiting forever while new readers are always
330 * accessing data (no progress). Enforce compiler-order of load
331 * rcu_reader ctr before store to rcu_gp_ctr.
9598a481 332 */
5481ddb3 333 cmm_barrier();
9598a481 334
5dba80f9 335 /*
5481ddb3 336 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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337 * model easier to understand. It does not have a big performance impact
338 * anyway, given this is the write-side.
339 */
5481ddb3 340 cmm_smp_mb();
67c2d80b 341
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342 /*
343 * Wait for previous parity to be empty of readers.
344 */
2dfb8b5e 345 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
9598a481 346
9598a481 347 /* Finish waiting for reader threads before letting the old ptr being
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348 * freed. Must be done within rcu_gp_lock because it iterates on reader
349 * threads. */
25cc6d18 350 smp_mb_master(RCU_MB_GROUP);
2dfb8b5e 351out:
6abb4bd5 352 mutex_unlock(&rcu_gp_lock);
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353}
354
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355/*
356 * library wrappers to be used by non-LGPL compatible source code.
357 */
358
359void rcu_read_lock(void)
360{
361 _rcu_read_lock();
362}
363
364void rcu_read_unlock(void)
365{
366 _rcu_read_unlock();
367}
368
121a5d44 369void rcu_register_thread(void)
27b012e2 370{
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371 rcu_reader.tid = pthread_self();
372 assert(rcu_reader.need_mb == 0);
4b5be3be 373 assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));
02be5561 374
6abb4bd5 375 mutex_lock(&rcu_gp_lock);
02be5561 376 rcu_init(); /* In case gcc does not support constructor attribute */
16aa9ee8 377 cds_list_add(&rcu_reader.node, &registry);
6abb4bd5 378 mutex_unlock(&rcu_gp_lock);
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379}
380
121a5d44 381void rcu_unregister_thread(void)
27b012e2 382{
6abb4bd5 383 mutex_lock(&rcu_gp_lock);
16aa9ee8 384 cds_list_del(&rcu_reader.node);
6abb4bd5 385 mutex_unlock(&rcu_gp_lock);
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386}
387
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388#ifdef RCU_MEMBARRIER
389void rcu_init(void)
390{
391 if (init_done)
392 return;
393 init_done = 1;
cf5271ee 394 if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
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395 has_sys_membarrier = 1;
396}
397#endif
398
399#ifdef RCU_SIGNAL
02be5561 400static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 401{
40e140c9 402 /*
5481ddb3
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403 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
404 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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405 * executed on.
406 */
5481ddb3 407 cmm_smp_mb();
6cf3827c 408 _CMM_STORE_SHARED(rcu_reader.need_mb, 0);
5481ddb3 409 cmm_smp_mb();
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410}
411
8a5fb4c9 412/*
02be5561 413 * rcu_init constructor. Called when the library is linked, but also when
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414 * reader threads are calling rcu_register_thread().
415 * Should only be called by a single thread at a given time. This is ensured by
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416 * holing the rcu_gp_lock from rcu_register_thread() or by running at library
417 * load time, which should not be executed by multiple threads nor concurrently
418 * with rcu_register_thread() anyway.
8a5fb4c9 419 */
02be5561 420void rcu_init(void)
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421{
422 struct sigaction act;
423 int ret;
424
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425 if (init_done)
426 return;
427 init_done = 1;
428
02be5561 429 act.sa_sigaction = sigrcu_handler;
dd052bd3 430 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 431 sigemptyset(&act.sa_mask);
02be5561 432 ret = sigaction(SIGRCU, &act, NULL);
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433 if (ret) {
434 perror("Error in sigaction");
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435 exit(-1);
436 }
437}
438
02be5561 439void rcu_exit(void)
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440{
441 struct sigaction act;
442 int ret;
443
02be5561 444 ret = sigaction(SIGRCU, NULL, &act);
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445 if (ret) {
446 perror("Error in sigaction");
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447 exit(-1);
448 }
02be5561 449 assert(act.sa_sigaction == sigrcu_handler);
16aa9ee8 450 assert(cds_list_empty(&registry));
27b012e2 451}
5e77fc1f 452
fdf01eed 453#endif /* #ifdef RCU_SIGNAL */
5e77fc1f 454
5e6b23a6 455DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 456
5e77fc1f 457#include "urcu-call-rcu-impl.h"
0376e7b2 458#include "urcu-defer-impl.h"
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