Add randomness to yield debug test
[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
22/* Global quiescent period parity */
23int urcu_qparity;
24
25int __thread urcu_active_readers[2];
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 */
68static int switch_next_urcu_qparity(void)
69{
70 int old_parity = urcu_qparity;
71 urcu_qparity = 1 - old_parity;
72 return old_parity;
73}
74
75static void force_mb_all_threads(void)
76{
f69f195a 77 struct reader_data *index;
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78 /*
79 * Ask for each threads to execute a mb() so we can consider the
80 * compiler barriers around rcu read lock as real memory barriers.
81 */
82 if (!reader_data)
83 return;
cf380c2f 84 debug_yield_write();
27b012e2 85 sig_done = 0;
cf380c2f 86 debug_yield_write();
f69f195a 87 mb(); /* write sig_done before sending the signals */
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88 debug_yield_write();
89 for (index = reader_data; index < reader_data + num_readers; index++) {
f69f195a 90 pthread_kill(index->tid, SIGURCU);
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91 debug_yield_write();
92 }
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93 /*
94 * Wait for sighandler (and thus mb()) to execute on every thread.
95 * BUSY-LOOP.
96 */
97 while (sig_done < num_readers)
98 barrier();
cf380c2f 99 debug_yield_write();
f69f195a 100 mb(); /* read sig_done before ending the barrier */
cf380c2f 101 debug_yield_write();
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102}
103
104void wait_for_quiescent_state(int parity)
105{
f69f195a 106 struct reader_data *index;
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107
108 if (!reader_data)
109 return;
110 /* Wait for each thread urcu_active_readers count to become 0.
111 */
f69f195a 112 for (index = reader_data; index < reader_data + num_readers; index++) {
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113 /*
114 * BUSY-LOOP.
115 */
f858d07a 116 while (index->urcu_active_readers[parity] != 0)
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117 barrier();
118 }
119 /*
120 * Locally : read *index->urcu_active_readers before freeing old
121 * pointer.
122 * Remote (reader threads) : Order urcu_qparity update and other
123 * thread's quiescent state counter read.
124 */
125 force_mb_all_threads();
126}
127
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128static void switch_qparity(void)
129{
130 int prev_parity;
131
132 /* All threads should read qparity before accessing data structure. */
133 /* Write ptr before changing the qparity */
134 force_mb_all_threads();
cf380c2f 135 debug_yield_write();
2bc59bd7 136 prev_parity = switch_next_urcu_qparity();
cf380c2f 137 debug_yield_write();
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138
139 /*
140 * Wait for previous parity to be empty of readers.
141 */
142 wait_for_quiescent_state(prev_parity);
143}
144
145void synchronize_rcu(void)
146{
cf380c2f 147 debug_yield_write();
c265818b 148 internal_urcu_lock();
cf380c2f 149 debug_yield_write();
2bc59bd7 150 switch_qparity();
cf380c2f 151 debug_yield_write();
2bc59bd7 152 switch_qparity();
cf380c2f 153 debug_yield_write();
c265818b 154 internal_urcu_lock();
cf380c2f 155 debug_yield_write();
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156}
157
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158/*
159 * Return old pointer, OK to free, no more reference exist.
41718ff9 160 * Called under rcu_write_lock.
27b012e2 161 */
cdcb92bb 162void *urcu_publish_content(void **ptr, void *new)
27b012e2 163{
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164 void *oldptr;
165
cf380c2f 166 debug_yield_write();
c265818b 167 internal_urcu_lock();
cf380c2f 168 debug_yield_write();
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169 /*
170 * We can publish the new pointer before we change the current qparity.
171 * Readers seeing the new pointer while being in the previous qparity
172 * window will make us wait until the end of the quiescent state before
173 * we release the unrelated memory area. However, given we hold the
174 * urcu_mutex, we are making sure that no further garbage collection can
175 * occur until we release the mutex, therefore we guarantee that this
176 * given reader will have completed its execution using the new pointer
177 * when the next quiescent state window will be over.
178 */
179 oldptr = *ptr;
cf380c2f 180 debug_yield_write();
27b012e2 181 *ptr = new;
27b012e2 182
cf380c2f 183 debug_yield_write();
2bc59bd7 184 switch_qparity();
cf380c2f 185 debug_yield_write();
2bc59bd7 186 switch_qparity();
cf380c2f 187 debug_yield_write();
c265818b 188 internal_urcu_unlock();
cf380c2f 189 debug_yield_write();
2bc59bd7 190
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191 return oldptr;
192}
193
194void urcu_add_reader(pthread_t id)
195{
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196 struct reader_data *oldarray;
197
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198 if (!reader_data) {
199 alloc_readers = INIT_NUM_THREADS;
f69f195a 200 num_readers = 0;
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201 reader_data =
202 malloc(sizeof(struct reader_data) * alloc_readers);
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203 }
204 if (alloc_readers < num_readers + 1) {
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205 oldarray = reader_data;
206 reader_data = malloc(sizeof(struct reader_data)
207 * (alloc_readers << 1));
208 memcpy(reader_data, oldarray,
209 sizeof(struct reader_data) * alloc_readers);
210 alloc_readers <<= 1;
211 free(oldarray);
212 }
213 reader_data[num_readers].tid = id;
214 /* reference to the TLS of _this_ reader thread. */
215 reader_data[num_readers].urcu_active_readers = urcu_active_readers;
216 num_readers++;
217}
218
219/*
220 * Never shrink (implementation limitation).
221 * This is O(nb threads). Eventually use a hash table.
222 */
223void urcu_remove_reader(pthread_t id)
224{
225 struct reader_data *index;
226
227 assert(reader_data != NULL);
228 for (index = reader_data; index < reader_data + num_readers; index++) {
e6d6e2dc 229 if (pthread_equal(index->tid, id)) {
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230 memcpy(index, &reader_data[num_readers - 1],
231 sizeof(struct reader_data));
232 reader_data[num_readers - 1].tid = 0;
233 reader_data[num_readers - 1].urcu_active_readers = NULL;
234 num_readers--;
235 return;
236 }
237 }
238 /* Hrm not found, forgot to register ? */
239 assert(0);
240}
241
242void urcu_register_thread(void)
243{
c265818b 244 internal_urcu_lock();
41718ff9 245 urcu_add_reader(pthread_self());
c265818b 246 internal_urcu_unlock();
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247}
248
f69f195a 249void urcu_unregister_thread(void)
27b012e2 250{
c265818b 251 internal_urcu_lock();
41718ff9 252 urcu_remove_reader(pthread_self());
c265818b 253 internal_urcu_unlock();
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254}
255
f69f195a 256void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
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257{
258 mb();
259 atomic_inc(&sig_done);
260}
261
262void __attribute__((constructor)) urcu_init(void)
263{
264 struct sigaction act;
265 int ret;
266
267 act.sa_sigaction = sigurcu_handler;
268 ret = sigaction(SIGURCU, &act, NULL);
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269 if (ret) {
270 perror("Error in sigaction");
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271 exit(-1);
272 }
273}
274
275void __attribute__((destructor)) urcu_exit(void)
276{
277 struct sigaction act;
278 int ret;
279
280 ret = sigaction(SIGURCU, NULL, &act);
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281 if (ret) {
282 perror("Error in sigaction");
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283 exit(-1);
284 }
285 assert(act.sa_sigaction == sigurcu_handler);
286 free(reader_data);
287}
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