update version to 0.5.0
[urcu.git] / urcu-qsbr.c
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9f1621ca 1/*
7ac06cef 2 * urcu-qsbr.c
9f1621ca 3 *
7ac06cef 4 * Userspace RCU QSBR library
9f1621ca 5 *
6982d6d7 6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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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
727f819d 35#define BUILD_QSBR_LIB
7ac06cef 36#include "urcu-qsbr-static.h"
9f1621ca 37/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
7ac06cef 38#include "urcu-qsbr.h"
9f1621ca 39
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40void __attribute__((destructor)) rcu_exit(void);
41
6abb4bd5 42static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
9f1621ca 43
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44int gp_futex;
45
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46/*
47 * Global grace period counter.
48 */
02be5561 49unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
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50
51/*
52 * Written to only by each individual reader. Read by both the reader and the
53 * writers.
54 */
02be5561 55struct rcu_reader __thread rcu_reader;
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56
57#ifdef DEBUG_YIELD
58unsigned int yield_active;
59unsigned int __thread rand_yield;
60#endif
61
16aa9ee8 62static CDS_LIST_HEAD(registry);
9f1621ca 63
6abb4bd5 64static void mutex_lock(pthread_mutex_t *mutex)
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65{
66 int ret;
67
68#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 69 ret = pthread_mutex_lock(mutex);
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70 if (ret) {
71 perror("Error in pthread mutex lock");
72 exit(-1);
73 }
74#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 75 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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76 if (ret != EBUSY && ret != EINTR) {
77 printf("ret = %d, errno = %d\n", ret, errno);
78 perror("Error in pthread mutex lock");
79 exit(-1);
80 }
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81 poll(NULL,0,10);
82 }
83#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
84}
85
6abb4bd5 86static void mutex_unlock(pthread_mutex_t *mutex)
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87{
88 int ret;
89
6abb4bd5 90 ret = pthread_mutex_unlock(mutex);
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91 if (ret) {
92 perror("Error in pthread mutex unlock");
93 exit(-1);
94 }
95}
96
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97/*
98 * synchronize_rcu() waiting. Single thread.
99 */
4d703340 100static void wait_gp(void)
bc6c15bb 101{
4d703340 102 /* Read reader_gp before read futex */
5481ddb3 103 cmm_smp_rmb();
4d703340 104 if (uatomic_read(&gp_futex) == -1)
0854ccff 105 futex_noasync(&gp_futex, FUTEX_WAIT, -1,
4d703340 106 NULL, NULL, 0);
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107}
108
2dfb8b5e 109static void update_counter_and_wait(void)
9f1621ca 110{
16aa9ee8 111 CDS_LIST_HEAD(qsreaders);
4d703340 112 int wait_loops = 0;
02be5561 113 struct rcu_reader *index, *tmp;
9f1621ca 114
2dfb8b5e 115#if (BITS_PER_LONG < 64)
32c15e4e 116 /* Switch parity: 0 -> 1, 1 -> 0 */
06f22bdb 117 CAA_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
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118#else /* !(BITS_PER_LONG < 64) */
119 /* Increment current G.P. */
06f22bdb 120 CAA_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
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121#endif /* !(BITS_PER_LONG < 64) */
122
7a5a38f5 123 /*
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124 * Must commit rcu_gp_ctr update to memory before waiting for quiescent
125 * state. Failure to do so could result in the writer waiting forever
126 * while new readers are always accessing data (no progress). Enforce
127 * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
128 */
5481ddb3 129 cmm_barrier();
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130
131 /*
5481ddb3 132 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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133 * model easier to understand. It does not have a big performance impact
134 * anyway, given this is the write-side.
7a5a38f5 135 */
5481ddb3 136 cmm_smp_mb();
7a5a38f5 137
9f1621ca 138 /*
3395d46c 139 * Wait for each thread rcu_reader_qs_gp count to become 0.
9f1621ca 140 */
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141 for (;;) {
142 wait_loops++;
143 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
144 uatomic_dec(&gp_futex);
145 /* Write futex before read reader_gp */
5481ddb3 146 cmm_smp_mb();
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147 }
148
16aa9ee8 149 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
4d703340 150 if (!rcu_gp_ongoing(&index->ctr))
16aa9ee8 151 cds_list_move(&index->node, &qsreaders);
4d703340 152 }
bc6c15bb 153
16aa9ee8 154 if (cds_list_empty(&registry)) {
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155 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
156 /* Read reader_gp before write futex */
5481ddb3 157 cmm_smp_mb();
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158 uatomic_set(&gp_futex, 0);
159 }
160 break;
161 } else {
162 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
163 wait_gp();
bc6c15bb 164 } else {
9f1621ca 165#ifndef HAS_INCOHERENT_CACHES
06f22bdb 166 caa_cpu_relax();
9f1621ca 167#else /* #ifndef HAS_INCOHERENT_CACHES */
5481ddb3 168 cmm_smp_mb();
9f1621ca 169#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
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170 }
171 }
9f1621ca 172 }
4d703340 173 /* put back the reader list in the registry */
16aa9ee8 174 cds_list_splice(&qsreaders, &registry);
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175}
176
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177/*
178 * Using a two-subphases algorithm for architectures with smaller than 64-bit
179 * long-size to ensure we do not encounter an overflow bug.
180 */
181
182#if (BITS_PER_LONG < 64)
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183void synchronize_rcu(void)
184{
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185 unsigned long was_online;
186
02be5561 187 was_online = rcu_reader.ctr;
bc49c323 188
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189 /* All threads should read qparity before accessing data structure
190 * where new ptr points to.
191 */
192 /* Write new ptr before changing the qparity */
5481ddb3 193 cmm_smp_mb();
47d2f29e 194
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195 /*
196 * Mark the writer thread offline to make sure we don't wait for
197 * our own quiescent state. This allows using synchronize_rcu() in
198 * threads registered as readers.
199 */
200 if (was_online)
06f22bdb 201 CAA_STORE_SHARED(rcu_reader.ctr, 0);
bc49c323 202
6abb4bd5 203 mutex_lock(&rcu_gp_lock);
47d2f29e 204
16aa9ee8 205 if (cds_list_empty(&registry))
2dfb8b5e 206 goto out;
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207
208 /*
209 * Wait for previous parity to be empty of readers.
210 */
2dfb8b5e 211 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
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212
213 /*
214 * Must finish waiting for quiescent state for parity 0 before
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215 * committing next rcu_gp_ctr update to memory. Failure to do so could
216 * result in the writer waiting forever while new readers are always
217 * accessing data (no progress). Enforce compiler-order of load
218 * rcu_reader ctr before store to rcu_gp_ctr.
47d2f29e 219 */
5481ddb3 220 cmm_barrier();
47d2f29e 221
47d2f29e 222 /*
5481ddb3 223 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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224 * model easier to understand. It does not have a big performance impact
225 * anyway, given this is the write-side.
47d2f29e 226 */
5481ddb3 227 cmm_smp_mb();
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228
229 /*
230 * Wait for previous parity to be empty of readers.
231 */
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232 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
233out:
6abb4bd5 234 mutex_unlock(&rcu_gp_lock);
47d2f29e 235
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236 /*
237 * Finish waiting for reader threads before letting the old ptr being
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238 * freed.
239 */
bc49c323 240 if (was_online)
06f22bdb 241 _CAA_STORE_SHARED(rcu_reader.ctr, CAA_LOAD_SHARED(rcu_gp_ctr));
5481ddb3 242 cmm_smp_mb();
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243}
244#else /* !(BITS_PER_LONG < 64) */
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245void synchronize_rcu(void)
246{
f0f7dbdd 247 unsigned long was_online;
ff2f67a0 248
02be5561 249 was_online = rcu_reader.ctr;
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250
251 /*
252 * Mark the writer thread offline to make sure we don't wait for
253 * our own quiescent state. This allows using synchronize_rcu() in
254 * threads registered as readers.
255 */
5481ddb3 256 cmm_smp_mb();
ff2f67a0 257 if (was_online)
06f22bdb 258 CAA_STORE_SHARED(rcu_reader.ctr, 0);
ff2f67a0 259
6abb4bd5 260 mutex_lock(&rcu_gp_lock);
16aa9ee8 261 if (cds_list_empty(&registry))
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262 goto out;
263 update_counter_and_wait();
264out:
6abb4bd5 265 mutex_unlock(&rcu_gp_lock);
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266
267 if (was_online)
06f22bdb 268 _CAA_STORE_SHARED(rcu_reader.ctr, CAA_LOAD_SHARED(rcu_gp_ctr));
5481ddb3 269 cmm_smp_mb();
9f1621ca 270}
47d2f29e 271#endif /* !(BITS_PER_LONG < 64) */
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272
273/*
274 * library wrappers to be used by non-LGPL compatible source code.
275 */
276
277void rcu_read_lock(void)
278{
279 _rcu_read_lock();
280}
281
282void rcu_read_unlock(void)
283{
284 _rcu_read_unlock();
285}
286
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287void rcu_quiescent_state(void)
288{
289 _rcu_quiescent_state();
290}
291
292void rcu_thread_offline(void)
293{
294 _rcu_thread_offline();
295}
296
297void rcu_thread_online(void)
298{
299 _rcu_thread_online();
300}
301
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302void rcu_register_thread(void)
303{
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304 rcu_reader.tid = pthread_self();
305 assert(rcu_reader.ctr == 0);
4f8e3380 306
6abb4bd5 307 mutex_lock(&rcu_gp_lock);
16aa9ee8 308 cds_list_add(&rcu_reader.node, &registry);
6abb4bd5 309 mutex_unlock(&rcu_gp_lock);
5f373c84 310 _rcu_thread_online();
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311}
312
313void rcu_unregister_thread(void)
314{
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315 /*
316 * We have to make the thread offline otherwise we end up dealocking
317 * with a waiting writer.
318 */
319 _rcu_thread_offline();
6abb4bd5 320 mutex_lock(&rcu_gp_lock);
16aa9ee8 321 cds_list_del(&rcu_reader.node);
6abb4bd5 322 mutex_unlock(&rcu_gp_lock);
9f1621ca 323}
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324
325void rcu_exit(void)
326{
16aa9ee8 327 assert(cds_list_empty(&registry));
f6d18c64 328}
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