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[urcu.git] / urcu-qsbr.c
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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
35#include "urcu-static.h"
36/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
37#include "urcu.h"
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 */
50long __thread urcu_active_readers;
51
52/* Thread IDs of registered readers */
53#define INIT_NUM_THREADS 4
54
55struct reader_registry {
56 pthread_t tid;
57 long *urcu_active_readers;
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 /*
127 * Wait for each thread urcu_active_readers count to become 0.
128 */
129 for (index = registry; index < registry + num_readers; index++) {
130#ifndef HAS_INCOHERENT_CACHES
131 while (rcu_old_gp_ongoing(index->urcu_active_readers))
132 cpu_relax();
133#else /* #ifndef HAS_INCOHERENT_CACHES */
134 int wait_loops = 0;
135 /*
136 * BUSY-LOOP. Force the reader thread to commit its
137 * urcu_active_readers update to memory if we wait for too long.
138 */
139 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
140 if (wait_loops++ == KICK_READER_LOOPS) {
141 force_mb_single_thread(index);
142 wait_loops = 0;
143 } else {
144 cpu_relax();
145 }
146 }
147#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
148 }
149}
150
151void synchronize_rcu(void)
152{
153 internal_urcu_lock();
154 force_mb_all_threads();
155 urcu_gp_ctr += 2;
156 wait_for_quiescent_state();
157 force_mb_all_threads();
158 internal_urcu_unlock();
159}
160
161/*
162 * library wrappers to be used by non-LGPL compatible source code.
163 */
164
165void rcu_read_lock(void)
166{
167 _rcu_read_lock();
168}
169
170void rcu_read_unlock(void)
171{
172 _rcu_read_unlock();
173}
174
175void *rcu_dereference(void *p)
176{
177 return _rcu_dereference(p);
178}
179
180void *rcu_assign_pointer_sym(void **p, void *v)
181{
182 wmb();
183 return STORE_SHARED(p, v);
184}
185
186void *rcu_xchg_pointer_sym(void **p, void *v)
187{
188 wmb();
189 return xchg(p, v);
190}
191
192void *rcu_publish_content_sym(void **p, void *v)
193{
194 void *oldptr;
195
196 oldptr = _rcu_xchg_pointer(p, v);
197 synchronize_rcu();
198 return oldptr;
199}
200
201static void rcu_add_reader(pthread_t id)
202{
203 struct reader_registry *oldarray;
204
205 if (!registry) {
206 alloc_readers = INIT_NUM_THREADS;
207 num_readers = 0;
208 registry =
209 malloc(sizeof(struct reader_registry) * alloc_readers);
210 }
211 if (alloc_readers < num_readers + 1) {
212 oldarray = registry;
213 registry = malloc(sizeof(struct reader_registry)
214 * (alloc_readers << 1));
215 memcpy(registry, oldarray,
216 sizeof(struct reader_registry) * alloc_readers);
217 alloc_readers <<= 1;
218 free(oldarray);
219 }
220 registry[num_readers].tid = id;
221 /* reference to the TLS of _this_ reader thread. */
222 registry[num_readers].urcu_active_readers = &urcu_active_readers;
223 registry[num_readers].need_mb = &need_mb;
224 num_readers++;
225}
226
227/*
228 * Never shrink (implementation limitation).
229 * This is O(nb threads). Eventually use a hash table.
230 */
231static void rcu_remove_reader(pthread_t id)
232{
233 struct reader_registry *index;
234
235 assert(registry != NULL);
236 for (index = registry; index < registry + num_readers; index++) {
237 if (pthread_equal(index->tid, id)) {
238 memcpy(index, &registry[num_readers - 1],
239 sizeof(struct reader_registry));
240 registry[num_readers - 1].tid = 0;
241 registry[num_readers - 1].urcu_active_readers = NULL;
242 num_readers--;
243 return;
244 }
245 }
246 /* Hrm not found, forgot to register ? */
247 assert(0);
248}
249
250void rcu_register_thread(void)
251{
252 internal_urcu_lock();
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253 rcu_add_reader(pthread_self());
254 internal_urcu_unlock();
255}
256
257void rcu_unregister_thread(void)
258{
259 internal_urcu_lock();
260 rcu_remove_reader(pthread_self());
261 internal_urcu_unlock();
262}
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