Raise the number of nested readers limit 2^16 and 2^32 on 32 and 64-bits arch.
[urcu.git] / urcu.c
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
6 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
7 *
8 * Distributed under GPLv2
9 */
10
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11#include <stdio.h>
12#include <pthread.h>
13#include <signal.h>
14#include <assert.h>
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15#include <stdlib.h>
16#include <string.h>
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17
18#include "urcu.h"
19
20pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
21
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22/* Global grace period counter */
23int urcu_gp_ctr;
27b012e2 24
1430ee0b 25int __thread urcu_active_readers;
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26
27/* Thread IDs of registered readers */
28#define INIT_NUM_THREADS 4
29
30struct reader_data {
31 pthread_t tid;
f69f195a 32 int *urcu_active_readers;
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33};
34
cf380c2f 35#ifdef DEBUG_YIELD
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36unsigned int yield_active;
37unsigned int __thread rand_yield;
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38#endif
39
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40static struct reader_data *reader_data;
41static int num_readers, alloc_readers;
42static int sig_done;
43
c265818b 44void internal_urcu_lock(void)
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45{
46 int ret;
47 ret = pthread_mutex_lock(&urcu_mutex);
48 if (ret) {
49 perror("Error in pthread mutex lock");
50 exit(-1);
51 }
52}
53
c265818b 54void internal_urcu_unlock(void)
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55{
56 int ret;
57
58 ret = pthread_mutex_unlock(&urcu_mutex);
59 if (ret) {
60 perror("Error in pthread mutex unlock");
61 exit(-1);
62 }
63}
64
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65/*
66 * called with urcu_mutex held.
67 */
1430ee0b 68static void switch_next_urcu_qparity(void)
27b012e2 69{
1430ee0b 70 urcu_gp_ctr ^= RCU_GP_CTR_BIT;
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71}
72
73static void force_mb_all_threads(void)
74{
f69f195a 75 struct reader_data *index;
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76 /*
77 * Ask for each threads to execute a mb() so we can consider the
78 * compiler barriers around rcu read lock as real memory barriers.
79 */
80 if (!reader_data)
81 return;
cf380c2f 82 debug_yield_write();
27b012e2 83 sig_done = 0;
cf380c2f 84 debug_yield_write();
f69f195a 85 mb(); /* write sig_done before sending the signals */
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86 debug_yield_write();
87 for (index = reader_data; index < reader_data + num_readers; index++) {
f69f195a 88 pthread_kill(index->tid, SIGURCU);
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89 debug_yield_write();
90 }
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91 /*
92 * Wait for sighandler (and thus mb()) to execute on every thread.
93 * BUSY-LOOP.
94 */
95 while (sig_done < num_readers)
96 barrier();
cf380c2f 97 debug_yield_write();
f69f195a 98 mb(); /* read sig_done before ending the barrier */
cf380c2f 99 debug_yield_write();
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100}
101
1430ee0b 102void wait_for_quiescent_state(void)
27b012e2 103{
f69f195a 104 struct reader_data *index;
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105
106 if (!reader_data)
107 return;
108 /* Wait for each thread urcu_active_readers count to become 0.
109 */
f69f195a 110 for (index = reader_data; index < reader_data + num_readers; index++) {
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111 /*
112 * BUSY-LOOP.
113 */
1430ee0b 114 while (rcu_old_gp_ongoing(index->urcu_active_readers))
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115 barrier();
116 }
117 /*
118 * Locally : read *index->urcu_active_readers before freeing old
119 * pointer.
120 * Remote (reader threads) : Order urcu_qparity update and other
121 * thread's quiescent state counter read.
122 */
123 force_mb_all_threads();
124}
125
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126static void switch_qparity(void)
127{
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128 /* All threads should read qparity before accessing data structure. */
129 /* Write ptr before changing the qparity */
130 force_mb_all_threads();
cf380c2f 131 debug_yield_write();
1430ee0b 132 switch_next_urcu_qparity();
cf380c2f 133 debug_yield_write();
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134
135 /*
136 * Wait for previous parity to be empty of readers.
137 */
1430ee0b 138 wait_for_quiescent_state();
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139}
140
141void synchronize_rcu(void)
142{
cf380c2f 143 debug_yield_write();
c265818b 144 internal_urcu_lock();
cf380c2f 145 debug_yield_write();
2bc59bd7 146 switch_qparity();
cf380c2f 147 debug_yield_write();
2bc59bd7 148 switch_qparity();
cf380c2f 149 debug_yield_write();
e7b43771 150 internal_urcu_unlock();
cf380c2f 151 debug_yield_write();
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152}
153
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154void urcu_add_reader(pthread_t id)
155{
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156 struct reader_data *oldarray;
157
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158 if (!reader_data) {
159 alloc_readers = INIT_NUM_THREADS;
f69f195a 160 num_readers = 0;
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161 reader_data =
162 malloc(sizeof(struct reader_data) * alloc_readers);
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163 }
164 if (alloc_readers < num_readers + 1) {
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165 oldarray = reader_data;
166 reader_data = malloc(sizeof(struct reader_data)
167 * (alloc_readers << 1));
168 memcpy(reader_data, oldarray,
169 sizeof(struct reader_data) * alloc_readers);
170 alloc_readers <<= 1;
171 free(oldarray);
172 }
173 reader_data[num_readers].tid = id;
174 /* reference to the TLS of _this_ reader thread. */
1430ee0b 175 reader_data[num_readers].urcu_active_readers = &urcu_active_readers;
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176 num_readers++;
177}
178
179/*
180 * Never shrink (implementation limitation).
181 * This is O(nb threads). Eventually use a hash table.
182 */
183void urcu_remove_reader(pthread_t id)
184{
185 struct reader_data *index;
186
187 assert(reader_data != NULL);
188 for (index = reader_data; index < reader_data + num_readers; index++) {
e6d6e2dc 189 if (pthread_equal(index->tid, id)) {
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190 memcpy(index, &reader_data[num_readers - 1],
191 sizeof(struct reader_data));
192 reader_data[num_readers - 1].tid = 0;
193 reader_data[num_readers - 1].urcu_active_readers = NULL;
194 num_readers--;
195 return;
196 }
197 }
198 /* Hrm not found, forgot to register ? */
199 assert(0);
200}
201
202void urcu_register_thread(void)
203{
c265818b 204 internal_urcu_lock();
41718ff9 205 urcu_add_reader(pthread_self());
c265818b 206 internal_urcu_unlock();
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207}
208
f69f195a 209void urcu_unregister_thread(void)
27b012e2 210{
c265818b 211 internal_urcu_lock();
41718ff9 212 urcu_remove_reader(pthread_self());
c265818b 213 internal_urcu_unlock();
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214}
215
f69f195a 216void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
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217{
218 mb();
219 atomic_inc(&sig_done);
220}
221
222void __attribute__((constructor)) urcu_init(void)
223{
224 struct sigaction act;
225 int ret;
226
227 act.sa_sigaction = sigurcu_handler;
228 ret = sigaction(SIGURCU, &act, NULL);
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229 if (ret) {
230 perror("Error in sigaction");
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231 exit(-1);
232 }
233}
234
235void __attribute__((destructor)) urcu_exit(void)
236{
237 struct sigaction act;
238 int ret;
239
240 ret = sigaction(SIGURCU, NULL, &act);
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241 if (ret) {
242 perror("Error in sigaction");
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243 exit(-1);
244 }
245 assert(act.sa_sigaction == sigurcu_handler);
246 free(reader_data);
247}
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