Add DEBUG_YIELD, add test duration
[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
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35#ifdef DEBUG_YIELD
36int yield_active;
37#endif
38
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39static struct reader_data *reader_data;
40static int num_readers, alloc_readers;
41static int sig_done;
42
c265818b 43void internal_urcu_lock(void)
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44{
45 int ret;
46 ret = pthread_mutex_lock(&urcu_mutex);
47 if (ret) {
48 perror("Error in pthread mutex lock");
49 exit(-1);
50 }
51}
52
c265818b 53void internal_urcu_unlock(void)
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54{
55 int ret;
56
57 ret = pthread_mutex_unlock(&urcu_mutex);
58 if (ret) {
59 perror("Error in pthread mutex unlock");
60 exit(-1);
61 }
62}
63
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64/*
65 * called with urcu_mutex held.
66 */
67static int switch_next_urcu_qparity(void)
68{
69 int old_parity = urcu_qparity;
70 urcu_qparity = 1 - old_parity;
71 return old_parity;
72}
73
74static void force_mb_all_threads(void)
75{
f69f195a 76 struct reader_data *index;
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77 /*
78 * Ask for each threads to execute a mb() so we can consider the
79 * compiler barriers around rcu read lock as real memory barriers.
80 */
81 if (!reader_data)
82 return;
cf380c2f 83 debug_yield_write();
27b012e2 84 sig_done = 0;
cf380c2f 85 debug_yield_write();
f69f195a 86 mb(); /* write sig_done before sending the signals */
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87 debug_yield_write();
88 for (index = reader_data; index < reader_data + num_readers; index++) {
f69f195a 89 pthread_kill(index->tid, SIGURCU);
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90 debug_yield_write();
91 }
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92 /*
93 * Wait for sighandler (and thus mb()) to execute on every thread.
94 * BUSY-LOOP.
95 */
96 while (sig_done < num_readers)
97 barrier();
cf380c2f 98 debug_yield_write();
f69f195a 99 mb(); /* read sig_done before ending the barrier */
cf380c2f 100 debug_yield_write();
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101}
102
103void wait_for_quiescent_state(int parity)
104{
f69f195a 105 struct reader_data *index;
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106
107 if (!reader_data)
108 return;
109 /* Wait for each thread urcu_active_readers count to become 0.
110 */
f69f195a 111 for (index = reader_data; index < reader_data + num_readers; index++) {
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112 /*
113 * BUSY-LOOP.
114 */
f858d07a 115 while (index->urcu_active_readers[parity] != 0)
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116 barrier();
117 }
118 /*
119 * Locally : read *index->urcu_active_readers before freeing old
120 * pointer.
121 * Remote (reader threads) : Order urcu_qparity update and other
122 * thread's quiescent state counter read.
123 */
124 force_mb_all_threads();
125}
126
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127static void switch_qparity(void)
128{
129 int prev_parity;
130
131 /* All threads should read qparity before accessing data structure. */
132 /* Write ptr before changing the qparity */
133 force_mb_all_threads();
cf380c2f 134 debug_yield_write();
2bc59bd7 135 prev_parity = switch_next_urcu_qparity();
cf380c2f 136 debug_yield_write();
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137
138 /*
139 * Wait for previous parity to be empty of readers.
140 */
141 wait_for_quiescent_state(prev_parity);
142}
143
144void synchronize_rcu(void)
145{
cf380c2f 146 debug_yield_write();
c265818b 147 internal_urcu_lock();
cf380c2f 148 debug_yield_write();
2bc59bd7 149 switch_qparity();
cf380c2f 150 debug_yield_write();
2bc59bd7 151 switch_qparity();
cf380c2f 152 debug_yield_write();
c265818b 153 internal_urcu_lock();
cf380c2f 154 debug_yield_write();
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155}
156
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157/*
158 * Return old pointer, OK to free, no more reference exist.
41718ff9 159 * Called under rcu_write_lock.
27b012e2 160 */
cdcb92bb 161void *urcu_publish_content(void **ptr, void *new)
27b012e2 162{
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163 void *oldptr;
164
cf380c2f 165 debug_yield_write();
c265818b 166 internal_urcu_lock();
cf380c2f 167 debug_yield_write();
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168 /*
169 * We can publish the new pointer before we change the current qparity.
170 * Readers seeing the new pointer while being in the previous qparity
171 * window will make us wait until the end of the quiescent state before
172 * we release the unrelated memory area. However, given we hold the
173 * urcu_mutex, we are making sure that no further garbage collection can
174 * occur until we release the mutex, therefore we guarantee that this
175 * given reader will have completed its execution using the new pointer
176 * when the next quiescent state window will be over.
177 */
178 oldptr = *ptr;
cf380c2f 179 debug_yield_write();
27b012e2 180 *ptr = new;
27b012e2 181
cf380c2f 182 debug_yield_write();
2bc59bd7 183 switch_qparity();
cf380c2f 184 debug_yield_write();
2bc59bd7 185 switch_qparity();
cf380c2f 186 debug_yield_write();
c265818b 187 internal_urcu_unlock();
cf380c2f 188 debug_yield_write();
2bc59bd7 189
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190 return oldptr;
191}
192
193void urcu_add_reader(pthread_t id)
194{
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195 struct reader_data *oldarray;
196
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197 if (!reader_data) {
198 alloc_readers = INIT_NUM_THREADS;
f69f195a 199 num_readers = 0;
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200 reader_data =
201 malloc(sizeof(struct reader_data) * alloc_readers);
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202 }
203 if (alloc_readers < num_readers + 1) {
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204 oldarray = reader_data;
205 reader_data = malloc(sizeof(struct reader_data)
206 * (alloc_readers << 1));
207 memcpy(reader_data, oldarray,
208 sizeof(struct reader_data) * alloc_readers);
209 alloc_readers <<= 1;
210 free(oldarray);
211 }
212 reader_data[num_readers].tid = id;
213 /* reference to the TLS of _this_ reader thread. */
214 reader_data[num_readers].urcu_active_readers = urcu_active_readers;
215 num_readers++;
216}
217
218/*
219 * Never shrink (implementation limitation).
220 * This is O(nb threads). Eventually use a hash table.
221 */
222void urcu_remove_reader(pthread_t id)
223{
224 struct reader_data *index;
225
226 assert(reader_data != NULL);
227 for (index = reader_data; index < reader_data + num_readers; index++) {
e6d6e2dc 228 if (pthread_equal(index->tid, id)) {
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229 memcpy(index, &reader_data[num_readers - 1],
230 sizeof(struct reader_data));
231 reader_data[num_readers - 1].tid = 0;
232 reader_data[num_readers - 1].urcu_active_readers = NULL;
233 num_readers--;
234 return;
235 }
236 }
237 /* Hrm not found, forgot to register ? */
238 assert(0);
239}
240
241void urcu_register_thread(void)
242{
c265818b 243 internal_urcu_lock();
41718ff9 244 urcu_add_reader(pthread_self());
c265818b 245 internal_urcu_unlock();
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246}
247
f69f195a 248void urcu_unregister_thread(void)
27b012e2 249{
c265818b 250 internal_urcu_lock();
41718ff9 251 urcu_remove_reader(pthread_self());
c265818b 252 internal_urcu_unlock();
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253}
254
f69f195a 255void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
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256{
257 mb();
258 atomic_inc(&sig_done);
259}
260
261void __attribute__((constructor)) urcu_init(void)
262{
263 struct sigaction act;
264 int ret;
265
266 act.sa_sigaction = sigurcu_handler;
267 ret = sigaction(SIGURCU, &act, NULL);
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268 if (ret) {
269 perror("Error in sigaction");
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270 exit(-1);
271 }
272}
273
274void __attribute__((destructor)) urcu_exit(void)
275{
276 struct sigaction act;
277 int ret;
278
279 ret = sigaction(SIGURCU, NULL, &act);
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280 if (ret) {
281 perror("Error in sigaction");
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282 exit(-1);
283 }
284 assert(act.sa_sigaction == sigurcu_handler);
285 free(reader_data);
286}
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