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[urcu.git] / urcu-qsbr.c
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9f1621ca 1/*
7ac06cef 2 * urcu-qsbr.c
9f1621ca 3 *
7ac06cef 4 * Userspace RCU QSBR library
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5 *
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
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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40pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
41
42/*
43 * Global grace period counter.
44 */
ac258107 45unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
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46
47/*
48 * Written to only by each individual reader. Read by both the reader and the
49 * writers.
50 */
f0f7dbdd 51unsigned long __thread rcu_reader_qs_gp;
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52
53/* Thread IDs of registered readers */
54#define INIT_NUM_THREADS 4
55
56struct reader_registry {
57 pthread_t tid;
f0f7dbdd 58 unsigned long *rcu_reader_qs_gp;
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59};
60
61#ifdef DEBUG_YIELD
62unsigned int yield_active;
63unsigned int __thread rand_yield;
64#endif
65
66static struct reader_registry *registry;
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67static int num_readers, alloc_readers;
68
90c1618a 69static void internal_urcu_lock(void)
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70{
71 int ret;
72
73#ifndef DISTRUST_SIGNALS_EXTREME
74 ret = pthread_mutex_lock(&urcu_mutex);
75 if (ret) {
76 perror("Error in pthread mutex lock");
77 exit(-1);
78 }
79#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
80 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
81 if (ret != EBUSY && ret != EINTR) {
82 printf("ret = %d, errno = %d\n", ret, errno);
83 perror("Error in pthread mutex lock");
84 exit(-1);
85 }
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86 poll(NULL,0,10);
87 }
88#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
89}
90
90c1618a 91static void internal_urcu_unlock(void)
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92{
93 int ret;
94
95 ret = pthread_mutex_unlock(&urcu_mutex);
96 if (ret) {
97 perror("Error in pthread mutex unlock");
98 exit(-1);
99 }
100}
101
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102#ifdef HAS_INCOHERENT_CACHES
103static void force_mb_single_thread(struct reader_registry *index)
104{
105 smp_mb();
106}
107#endif /* #ifdef HAS_INCOHERENT_CACHES */
108
90c1618a 109static void wait_for_quiescent_state(void)
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110{
111 struct reader_registry *index;
112
113 if (!registry)
114 return;
115 /*
3395d46c 116 * Wait for each thread rcu_reader_qs_gp count to become 0.
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117 */
118 for (index = registry; index < registry + num_readers; index++) {
119#ifndef HAS_INCOHERENT_CACHES
4e560c17 120 while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
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121 cpu_relax();
122#else /* #ifndef HAS_INCOHERENT_CACHES */
123 int wait_loops = 0;
124 /*
125 * BUSY-LOOP. Force the reader thread to commit its
3395d46c 126 * rcu_reader_qs_gp update to memory if we wait for too long.
9f1621ca 127 */
4e560c17 128 while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
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129 if (wait_loops++ == KICK_READER_LOOPS) {
130 force_mb_single_thread(index);
131 wait_loops = 0;
132 } else {
133 cpu_relax();
134 }
135 }
136#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
137 }
138}
139
140void synchronize_rcu(void)
141{
f0f7dbdd 142 unsigned long was_online;
ff2f67a0 143
ab179a17 144 was_online = rcu_reader_qs_gp;
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145
146 /*
147 * Mark the writer thread offline to make sure we don't wait for
148 * our own quiescent state. This allows using synchronize_rcu() in
149 * threads registered as readers.
150 */
8f50d1ce 151 smp_mb();
ff2f67a0 152 if (was_online)
8f50d1ce 153 STORE_SHARED(rcu_reader_qs_gp, 0);
ff2f67a0 154
4e27f058 155 internal_urcu_lock();
55570466 156 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca 157 wait_for_quiescent_state();
9f1621ca 158 internal_urcu_unlock();
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159
160 if (was_online)
ab179a17 161 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
8f50d1ce 162 smp_mb();
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163}
164
165/*
166 * library wrappers to be used by non-LGPL compatible source code.
167 */
168
169void rcu_read_lock(void)
170{
171 _rcu_read_lock();
172}
173
174void rcu_read_unlock(void)
175{
176 _rcu_read_unlock();
177}
178
179void *rcu_dereference(void *p)
180{
181 return _rcu_dereference(p);
182}
183
184void *rcu_assign_pointer_sym(void **p, void *v)
185{
186 wmb();
187 return STORE_SHARED(p, v);
188}
189
190void *rcu_xchg_pointer_sym(void **p, void *v)
191{
192 wmb();
193 return xchg(p, v);
194}
195
196void *rcu_publish_content_sym(void **p, void *v)
197{
198 void *oldptr;
199
200 oldptr = _rcu_xchg_pointer(p, v);
201 synchronize_rcu();
202 return oldptr;
203}
204
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205void rcu_quiescent_state(void)
206{
207 _rcu_quiescent_state();
208}
209
210void rcu_thread_offline(void)
211{
212 _rcu_thread_offline();
213}
214
215void rcu_thread_online(void)
216{
217 _rcu_thread_online();
218}
219
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220static void rcu_add_reader(pthread_t id)
221{
222 struct reader_registry *oldarray;
223
224 if (!registry) {
225 alloc_readers = INIT_NUM_THREADS;
226 num_readers = 0;
227 registry =
228 malloc(sizeof(struct reader_registry) * alloc_readers);
229 }
230 if (alloc_readers < num_readers + 1) {
231 oldarray = registry;
232 registry = malloc(sizeof(struct reader_registry)
233 * (alloc_readers << 1));
234 memcpy(registry, oldarray,
235 sizeof(struct reader_registry) * alloc_readers);
236 alloc_readers <<= 1;
237 free(oldarray);
238 }
239 registry[num_readers].tid = id;
240 /* reference to the TLS of _this_ reader thread. */
3395d46c 241 registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
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242 num_readers++;
243}
244
245/*
246 * Never shrink (implementation limitation).
247 * This is O(nb threads). Eventually use a hash table.
248 */
249static void rcu_remove_reader(pthread_t id)
250{
251 struct reader_registry *index;
252
253 assert(registry != NULL);
254 for (index = registry; index < registry + num_readers; index++) {
255 if (pthread_equal(index->tid, id)) {
256 memcpy(index, &registry[num_readers - 1],
257 sizeof(struct reader_registry));
258 registry[num_readers - 1].tid = 0;
3395d46c 259 registry[num_readers - 1].rcu_reader_qs_gp = NULL;
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260 num_readers--;
261 return;
262 }
263 }
264 /* Hrm not found, forgot to register ? */
265 assert(0);
266}
267
268void rcu_register_thread(void)
269{
270 internal_urcu_lock();
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271 rcu_add_reader(pthread_self());
272 internal_urcu_unlock();
5f373c84 273 _rcu_thread_online();
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274}
275
276void rcu_unregister_thread(void)
277{
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278 /*
279 * We have to make the thread offline otherwise we end up dealocking
280 * with a waiting writer.
281 */
282 _rcu_thread_offline();
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283 internal_urcu_lock();
284 rcu_remove_reader(pthread_self());
285 internal_urcu_unlock();
286}
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