Fix static linking: add missing static to thr_defer
[urcu.git] / urcu-qsbr.c
CommitLineData
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
c1d2c60b 26#define _GNU_SOURCE
71c811bf 27#define _LGPL_SOURCE
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28#include <stdio.h>
29#include <pthread.h>
30#include <signal.h>
31#include <assert.h>
32#include <stdlib.h>
6d841bc2 33#include <stdint.h>
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34#include <string.h>
35#include <errno.h>
36#include <poll.h>
37
d73fb81f 38#include "urcu/wfcqueue.h"
57760d44 39#include "urcu/map/urcu-qsbr.h"
727f819d 40#define BUILD_QSBR_LIB
af7c2dbe 41#include "urcu/static/urcu-qsbr.h"
618b2595 42#include "urcu-pointer.h"
bd252a04 43#include "urcu/tls-compat.h"
71c811bf 44
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45#include "urcu-die.h"
46
9f1621ca 47/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf 48#undef _LGPL_SOURCE
7ac06cef 49#include "urcu-qsbr.h"
71c811bf 50#define _LGPL_SOURCE
9f1621ca 51
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MD
52void __attribute__((destructor)) rcu_exit(void);
53
6abb4bd5 54static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
9f1621ca 55
6d841bc2 56int32_t gp_futex;
bc6c15bb 57
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58/*
59 * Global grace period counter.
60 */
02be5561 61unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
9f1621ca 62
408f6d92
PB
63/*
64 * Active attempts to check for reader Q.S. before calling futex().
65 */
66#define RCU_QS_ACTIVE_ATTEMPTS 100
67
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68/*
69 * Written to only by each individual reader. Read by both the reader and the
70 * writers.
71 */
bd252a04 72DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
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73
74#ifdef DEBUG_YIELD
75unsigned int yield_active;
bd252a04 76DEFINE_URCU_TLS(unsigned int, rand_yield);
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77#endif
78
16aa9ee8 79static CDS_LIST_HEAD(registry);
9f1621ca 80
6abb4bd5 81static void mutex_lock(pthread_mutex_t *mutex)
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82{
83 int ret;
84
85#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 86 ret = pthread_mutex_lock(mutex);
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87 if (ret)
88 urcu_die(ret);
9f1621ca 89#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 90 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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91 if (ret != EBUSY && ret != EINTR)
92 urcu_die(ret);
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93 poll(NULL,0,10);
94 }
95#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
96}
97
6abb4bd5 98static void mutex_unlock(pthread_mutex_t *mutex)
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99{
100 int ret;
101
6abb4bd5 102 ret = pthread_mutex_unlock(mutex);
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103 if (ret)
104 urcu_die(ret);
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105}
106
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107/*
108 * synchronize_rcu() waiting. Single thread.
109 */
4d703340 110static void wait_gp(void)
bc6c15bb 111{
4d703340 112 /* Read reader_gp before read futex */
5481ddb3 113 cmm_smp_rmb();
4d703340 114 if (uatomic_read(&gp_futex) == -1)
0854ccff 115 futex_noasync(&gp_futex, FUTEX_WAIT, -1,
4d703340 116 NULL, NULL, 0);
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117}
118
2dfb8b5e 119static void update_counter_and_wait(void)
9f1621ca 120{
16aa9ee8 121 CDS_LIST_HEAD(qsreaders);
4d703340 122 int wait_loops = 0;
02be5561 123 struct rcu_reader *index, *tmp;
9f1621ca 124
b39e1761 125#if (CAA_BITS_PER_LONG < 64)
32c15e4e 126 /* Switch parity: 0 -> 1, 1 -> 0 */
6cf3827c 127 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
b39e1761 128#else /* !(CAA_BITS_PER_LONG < 64) */
2dfb8b5e 129 /* Increment current G.P. */
6cf3827c 130 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
b39e1761 131#endif /* !(CAA_BITS_PER_LONG < 64) */
2dfb8b5e 132
7a5a38f5 133 /*
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134 * Must commit rcu_gp_ctr update to memory before waiting for
135 * quiescent state. Failure to do so could result in the writer
136 * waiting forever while new readers are always accessing data
137 * (no progress). Enforce compiler-order of store to rcu_gp_ctr
bd252a04 138 * before load URCU_TLS(rcu_reader).ctr.
d40fde2c 139 */
5481ddb3 140 cmm_barrier();
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141
142 /*
5481ddb3 143 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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144 * model easier to understand. It does not have a big performance impact
145 * anyway, given this is the write-side.
7a5a38f5 146 */
5481ddb3 147 cmm_smp_mb();
7a5a38f5 148
9f1621ca 149 /*
3395d46c 150 * Wait for each thread rcu_reader_qs_gp count to become 0.
9f1621ca 151 */
4d703340
MD
152 for (;;) {
153 wait_loops++;
83a2c421
PB
154 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
155 uatomic_set(&gp_futex, -1);
156 /*
157 * Write futex before write waiting (the other side
158 * reads them in the opposite order).
159 */
160 cmm_smp_wmb();
161 cds_list_for_each_entry(index, &registry, node) {
162 _CMM_STORE_SHARED(index->waiting, 1);
163 }
4d703340 164 /* Write futex before read reader_gp */
5481ddb3 165 cmm_smp_mb();
4d703340 166 }
16aa9ee8 167 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
4d703340 168 if (!rcu_gp_ongoing(&index->ctr))
16aa9ee8 169 cds_list_move(&index->node, &qsreaders);
4d703340 170 }
bc6c15bb 171
16aa9ee8 172 if (cds_list_empty(&registry)) {
83a2c421 173 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
4d703340 174 /* Read reader_gp before write futex */
5481ddb3 175 cmm_smp_mb();
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176 uatomic_set(&gp_futex, 0);
177 }
178 break;
179 } else {
83a2c421 180 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
4d703340 181 wait_gp();
bc6c15bb 182 } else {
9f1621ca 183#ifndef HAS_INCOHERENT_CACHES
06f22bdb 184 caa_cpu_relax();
9f1621ca 185#else /* #ifndef HAS_INCOHERENT_CACHES */
5481ddb3 186 cmm_smp_mb();
9f1621ca 187#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
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188 }
189 }
9f1621ca 190 }
4d703340 191 /* put back the reader list in the registry */
16aa9ee8 192 cds_list_splice(&qsreaders, &registry);
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193}
194
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195/*
196 * Using a two-subphases algorithm for architectures with smaller than 64-bit
197 * long-size to ensure we do not encounter an overflow bug.
198 */
199
b39e1761 200#if (CAA_BITS_PER_LONG < 64)
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201void synchronize_rcu(void)
202{
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203 unsigned long was_online;
204
bd252a04 205 was_online = URCU_TLS(rcu_reader).ctr;
bc49c323 206
47d2f29e 207 /* All threads should read qparity before accessing data structure
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208 * where new ptr points to. In the "then" case, rcu_thread_offline
209 * includes a memory barrier.
210 *
bc49c323 211 * Mark the writer thread offline to make sure we don't wait for
5e77fc1f
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212 * our own quiescent state. This allows using synchronize_rcu()
213 * in threads registered as readers.
bc49c323 214 */
27b940e7
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215 if (was_online)
216 rcu_thread_offline();
217 else
218 cmm_smp_mb();
bc49c323 219
6abb4bd5 220 mutex_lock(&rcu_gp_lock);
47d2f29e 221
16aa9ee8 222 if (cds_list_empty(&registry))
2dfb8b5e 223 goto out;
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224
225 /*
226 * Wait for previous parity to be empty of readers.
227 */
2dfb8b5e 228 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
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229
230 /*
231 * Must finish waiting for quiescent state for parity 0 before
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232 * committing next rcu_gp_ctr update to memory. Failure to
233 * do so could result in the writer waiting forever while new
234 * readers are always accessing data (no progress). Enforce
bd252a04 235 * compiler-order of load URCU_TLS(rcu_reader).ctr before store to
5e77fc1f 236 * rcu_gp_ctr.
47d2f29e 237 */
5481ddb3 238 cmm_barrier();
47d2f29e 239
47d2f29e 240 /*
5481ddb3 241 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
2dfb8b5e
MD
242 * model easier to understand. It does not have a big performance impact
243 * anyway, given this is the write-side.
47d2f29e 244 */
5481ddb3 245 cmm_smp_mb();
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246
247 /*
248 * Wait for previous parity to be empty of readers.
249 */
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250 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
251out:
6abb4bd5 252 mutex_unlock(&rcu_gp_lock);
47d2f29e 253
bc49c323
MD
254 /*
255 * Finish waiting for reader threads before letting the old ptr being
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MD
256 * freed.
257 */
bc49c323 258 if (was_online)
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PB
259 rcu_thread_online();
260 else
261 cmm_smp_mb();
47d2f29e 262}
b39e1761 263#else /* !(CAA_BITS_PER_LONG < 64) */
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264void synchronize_rcu(void)
265{
f0f7dbdd 266 unsigned long was_online;
ff2f67a0 267
bd252a04 268 was_online = URCU_TLS(rcu_reader).ctr;
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MD
269
270 /*
271 * Mark the writer thread offline to make sure we don't wait for
5e77fc1f
PM
272 * our own quiescent state. This allows using synchronize_rcu()
273 * in threads registered as readers.
ff2f67a0 274 */
27b940e7
PB
275 if (was_online)
276 rcu_thread_offline();
277 else
278 cmm_smp_mb();
ff2f67a0 279
6abb4bd5 280 mutex_lock(&rcu_gp_lock);
16aa9ee8 281 if (cds_list_empty(&registry))
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MD
282 goto out;
283 update_counter_and_wait();
284out:
6abb4bd5 285 mutex_unlock(&rcu_gp_lock);
ff2f67a0
MD
286
287 if (was_online)
27b940e7
PB
288 rcu_thread_online();
289 else
290 cmm_smp_mb();
9f1621ca 291}
b39e1761 292#endif /* !(CAA_BITS_PER_LONG < 64) */
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MD
293
294/*
295 * library wrappers to be used by non-LGPL compatible source code.
296 */
297
298void rcu_read_lock(void)
299{
300 _rcu_read_lock();
301}
302
303void rcu_read_unlock(void)
304{
305 _rcu_read_unlock();
306}
307
7ac06cef
MD
308void rcu_quiescent_state(void)
309{
310 _rcu_quiescent_state();
311}
312
313void rcu_thread_offline(void)
314{
315 _rcu_thread_offline();
316}
317
318void rcu_thread_online(void)
319{
320 _rcu_thread_online();
321}
322
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323void rcu_register_thread(void)
324{
bd252a04
MD
325 URCU_TLS(rcu_reader).tid = pthread_self();
326 assert(URCU_TLS(rcu_reader).ctr == 0);
4f8e3380 327
6abb4bd5 328 mutex_lock(&rcu_gp_lock);
bd252a04 329 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
6abb4bd5 330 mutex_unlock(&rcu_gp_lock);
5f373c84 331 _rcu_thread_online();
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332}
333
334void rcu_unregister_thread(void)
335{
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MD
336 /*
337 * We have to make the thread offline otherwise we end up dealocking
338 * with a waiting writer.
339 */
340 _rcu_thread_offline();
6abb4bd5 341 mutex_lock(&rcu_gp_lock);
bd252a04 342 cds_list_del(&URCU_TLS(rcu_reader).node);
6abb4bd5 343 mutex_unlock(&rcu_gp_lock);
9f1621ca 344}
f6d18c64
MD
345
346void rcu_exit(void)
347{
01cadde4
MD
348 /*
349 * Assertion disabled because call_rcu threads are now rcu
350 * readers, and left running at exit.
351 * assert(cds_list_empty(&registry));
352 */
f6d18c64 353}
5e77fc1f 354
5e6b23a6 355DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 356
5e77fc1f 357#include "urcu-call-rcu-impl.h"
0376e7b2 358#include "urcu-defer-impl.h"
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