urcu qsbr: add DEBUG_RCU self check
[urcu.git] / urcu-qsbr.c
CommitLineData
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
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
3395d46c 35#include "urcu-qsbr.h"
9f1621ca 36/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
3395d46c 37//#include "urcu.h"
9f1621ca 38
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39pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
40
41/*
42 * Global grace period counter.
43 */
44long urcu_gp_ctr = 0;
45
46/*
47 * Written to only by each individual reader. Read by both the reader and the
48 * writers.
49 */
3395d46c 50long __thread rcu_reader_qs_gp;
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51
52/* Thread IDs of registered readers */
53#define INIT_NUM_THREADS 4
54
55struct reader_registry {
56 pthread_t tid;
3395d46c 57 long *rcu_reader_qs_gp;
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58 char *need_mb;
59};
60
61#ifdef DEBUG_YIELD
62unsigned int yield_active;
63unsigned int __thread rand_yield;
64#endif
65
66static struct reader_registry *registry;
67static char __thread need_mb;
68static int num_readers, alloc_readers;
69
70void internal_urcu_lock(void)
71{
72 int ret;
73
74#ifndef DISTRUST_SIGNALS_EXTREME
75 ret = pthread_mutex_lock(&urcu_mutex);
76 if (ret) {
77 perror("Error in pthread mutex lock");
78 exit(-1);
79 }
80#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
81 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
82 if (ret != EBUSY && ret != EINTR) {
83 printf("ret = %d, errno = %d\n", ret, errno);
84 perror("Error in pthread mutex lock");
85 exit(-1);
86 }
87 if (need_mb) {
88 smp_mb();
89 need_mb = 0;
90 smp_mb();
91 }
92 poll(NULL,0,10);
93 }
94#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
95}
96
97void internal_urcu_unlock(void)
98{
99 int ret;
100
101 ret = pthread_mutex_unlock(&urcu_mutex);
102 if (ret) {
103 perror("Error in pthread mutex unlock");
104 exit(-1);
105 }
106}
107
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108#ifdef HAS_INCOHERENT_CACHES
109static void force_mb_single_thread(struct reader_registry *index)
110{
111 smp_mb();
112}
113#endif /* #ifdef HAS_INCOHERENT_CACHES */
114
115static void force_mb_all_threads(void)
116{
117 smp_mb();
118}
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119
120void wait_for_quiescent_state(void)
121{
122 struct reader_registry *index;
123
124 if (!registry)
125 return;
126 /*
3395d46c 127 * Wait for each thread rcu_reader_qs_gp count to become 0.
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128 */
129 for (index = registry; index < registry + num_readers; index++) {
130#ifndef HAS_INCOHERENT_CACHES
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131 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
132 (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
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133 cpu_relax();
134#else /* #ifndef HAS_INCOHERENT_CACHES */
135 int wait_loops = 0;
136 /*
137 * BUSY-LOOP. Force the reader thread to commit its
3395d46c 138 * rcu_reader_qs_gp update to memory if we wait for too long.
9f1621ca 139 */
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140 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
141 (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
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142 if (wait_loops++ == KICK_READER_LOOPS) {
143 force_mb_single_thread(index);
144 wait_loops = 0;
145 } else {
146 cpu_relax();
147 }
148 }
149#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
150 }
151}
152
153void synchronize_rcu(void)
154{
155 internal_urcu_lock();
156 force_mb_all_threads();
157 urcu_gp_ctr += 2;
158 wait_for_quiescent_state();
159 force_mb_all_threads();
160 internal_urcu_unlock();
161}
162
163/*
164 * library wrappers to be used by non-LGPL compatible source code.
165 */
166
167void rcu_read_lock(void)
168{
169 _rcu_read_lock();
170}
171
172void rcu_read_unlock(void)
173{
174 _rcu_read_unlock();
175}
176
177void *rcu_dereference(void *p)
178{
179 return _rcu_dereference(p);
180}
181
182void *rcu_assign_pointer_sym(void **p, void *v)
183{
184 wmb();
185 return STORE_SHARED(p, v);
186}
187
188void *rcu_xchg_pointer_sym(void **p, void *v)
189{
190 wmb();
191 return xchg(p, v);
192}
193
194void *rcu_publish_content_sym(void **p, void *v)
195{
196 void *oldptr;
197
198 oldptr = _rcu_xchg_pointer(p, v);
199 synchronize_rcu();
200 return oldptr;
201}
202
203static void rcu_add_reader(pthread_t id)
204{
205 struct reader_registry *oldarray;
206
207 if (!registry) {
208 alloc_readers = INIT_NUM_THREADS;
209 num_readers = 0;
210 registry =
211 malloc(sizeof(struct reader_registry) * alloc_readers);
212 }
213 if (alloc_readers < num_readers + 1) {
214 oldarray = registry;
215 registry = malloc(sizeof(struct reader_registry)
216 * (alloc_readers << 1));
217 memcpy(registry, oldarray,
218 sizeof(struct reader_registry) * alloc_readers);
219 alloc_readers <<= 1;
220 free(oldarray);
221 }
222 registry[num_readers].tid = id;
223 /* reference to the TLS of _this_ reader thread. */
3395d46c 224 registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
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225 registry[num_readers].need_mb = &need_mb;
226 num_readers++;
227}
228
229/*
230 * Never shrink (implementation limitation).
231 * This is O(nb threads). Eventually use a hash table.
232 */
233static void rcu_remove_reader(pthread_t id)
234{
235 struct reader_registry *index;
236
237 assert(registry != NULL);
238 for (index = registry; index < registry + num_readers; index++) {
239 if (pthread_equal(index->tid, id)) {
240 memcpy(index, &registry[num_readers - 1],
241 sizeof(struct reader_registry));
242 registry[num_readers - 1].tid = 0;
3395d46c 243 registry[num_readers - 1].rcu_reader_qs_gp = NULL;
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244 num_readers--;
245 return;
246 }
247 }
248 /* Hrm not found, forgot to register ? */
249 assert(0);
250}
251
252void rcu_register_thread(void)
253{
254 internal_urcu_lock();
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255 rcu_add_reader(pthread_self());
256 internal_urcu_unlock();
5f373c84 257 _rcu_thread_online();
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258}
259
260void rcu_unregister_thread(void)
261{
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262 /*
263 * We have to make the thread offline otherwise we end up dealocking
264 * with a waiting writer.
265 */
266 _rcu_thread_offline();
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267 internal_urcu_lock();
268 rcu_remove_reader(pthread_self());
269 internal_urcu_unlock();
270}
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