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[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/*
23 * Global grace period counter.
24 * Contains the current RCU_GP_CTR_BIT.
25 * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
26 */
27long urcu_gp_ctr = RCU_GP_COUNT;
27b012e2 28
6e8b8429 29long __thread urcu_active_readers;
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30
31/* Thread IDs of registered readers */
32#define INIT_NUM_THREADS 4
33
34struct reader_data {
35 pthread_t tid;
128166c9 36 long *urcu_active_readers;
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37};
38
cf380c2f 39#ifdef DEBUG_YIELD
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40unsigned int yield_active;
41unsigned int __thread rand_yield;
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42#endif
43
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44static struct reader_data *reader_data;
45static int num_readers, alloc_readers;
b715b99e 46#ifndef DEBUG_FULL_MB
27b012e2 47static int sig_done;
b715b99e 48#endif
27b012e2 49
c265818b 50void internal_urcu_lock(void)
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51{
52 int ret;
53 ret = pthread_mutex_lock(&urcu_mutex);
54 if (ret) {
55 perror("Error in pthread mutex lock");
56 exit(-1);
57 }
58}
59
c265818b 60void internal_urcu_unlock(void)
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61{
62 int ret;
63
64 ret = pthread_mutex_unlock(&urcu_mutex);
65 if (ret) {
66 perror("Error in pthread mutex unlock");
67 exit(-1);
68 }
69}
70
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71/*
72 * called with urcu_mutex held.
73 */
1430ee0b 74static void switch_next_urcu_qparity(void)
27b012e2 75{
1430ee0b 76 urcu_gp_ctr ^= RCU_GP_CTR_BIT;
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77}
78
bb488185 79#ifdef DEBUG_FULL_MB
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80static void force_mb_single_thread(pthread_t tid)
81{
82 smp_mb();
83}
84
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85static void force_mb_all_threads(void)
86{
b715b99e 87 smp_mb();
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88}
89#else
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90
91static void force_mb_single_thread(pthread_t tid)
92{
93 assert(reader_data);
94 sig_done = 0;
95 smp_mb(); /* write sig_done before sending the signals */
96 pthread_kill(tid, SIGURCU);
97 /*
98 * Wait for sighandler (and thus mb()) to execute on every thread.
99 * BUSY-LOOP.
100 */
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101 while (LOAD_REMOTE(sig_done) < 1)
102 cpu_relax();
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103 smp_mb(); /* read sig_done before ending the barrier */
104}
105
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106static void force_mb_all_threads(void)
107{
f69f195a 108 struct reader_data *index;
27b012e2 109 /*
b715b99e 110 * Ask for each threads to execute a smp_mb() so we can consider the
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111 * compiler barriers around rcu read lock as real memory barriers.
112 */
113 if (!reader_data)
114 return;
27b012e2 115 sig_done = 0;
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116 /*
117 * pthread_kill has a smp_mb(). But beware, we assume it performs
118 * a cache flush on architectures with non-coherent cache.
119 * smp_mb(); write sig_done before sending the signals
120 */
ae878d0d 121 for (index = reader_data; index < reader_data + num_readers; index++)
f69f195a 122 pthread_kill(index->tid, SIGURCU);
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123 /*
124 * Wait for sighandler (and thus mb()) to execute on every thread.
125 * BUSY-LOOP.
126 */
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127 while (LOAD_REMOTE(sig_done) < num_readers)
128 cpu_relax();
b715b99e 129 smp_mb(); /* read sig_done before ending the barrier */
27b012e2 130}
bb488185 131#endif
27b012e2 132
1430ee0b 133void wait_for_quiescent_state(void)
27b012e2 134{
f69f195a 135 struct reader_data *index;
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136
137 if (!reader_data)
138 return;
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139 /*
140 * Wait for each thread urcu_active_readers count to become 0.
27b012e2 141 */
f69f195a 142 for (index = reader_data; index < reader_data + num_readers; index++) {
40e140c9 143 int wait_loops = 0;
27b012e2 144 /*
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145 * BUSY-LOOP. Force the reader thread to commit its
146 * urcu_active_readers update to memory if we wait for too long.
27b012e2 147 */
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148 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
149 if (wait_loops++ == KICK_READER_LOOPS) {
150 force_mb_single_thread(index->tid);
151 wait_loops = 0;
152 }
153 }
27b012e2 154 }
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155}
156
9598a481 157void synchronize_rcu(void)
2bc59bd7 158{
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159 internal_urcu_lock();
160
9598a481 161 /* All threads should read qparity before accessing data structure
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162 * where new ptr points to. Must be done within internal_urcu_lock
163 * because it iterates on reader threads.*/
9598a481 164 /* Write new ptr before changing the qparity */
2bc59bd7 165 force_mb_all_threads();
9598a481 166
9598a481 167 switch_next_urcu_qparity(); /* 0 -> 1 */
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168
169 /*
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170 * Must commit qparity update to memory before waiting for parity
171 * 0 quiescent state. Failure to do so could result in the writer
172 * waiting forever while new readers are always accessing data (no
173 * progress).
2bc59bd7 174 */
3a86deba 175 smp_mc();
2bc59bd7 176
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177 /*
178 * Wait for previous parity to be empty of readers.
179 */
180 wait_for_quiescent_state(); /* Wait readers in parity 0 */
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181
182 /*
183 * Must finish waiting for quiescent state for parity 0 before
184 * committing qparity update to memory. Failure to do so could result in
185 * the writer waiting forever while new readers are always accessing
186 * data (no progress).
187 */
3a86deba 188 smp_mc();
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189
190 switch_next_urcu_qparity(); /* 1 -> 0 */
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191
192 /*
193 * Must commit qparity update to memory before waiting for parity
194 * 1 quiescent state. Failure to do so could result in the writer
195 * waiting forever while new readers are always accessing data (no
196 * progress).
197 */
3a86deba 198 smp_mc();
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199
200 /*
201 * Wait for previous parity to be empty of readers.
202 */
203 wait_for_quiescent_state(); /* Wait readers in parity 1 */
9598a481 204
9598a481 205 /* Finish waiting for reader threads before letting the old ptr being
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206 * freed. Must be done within internal_urcu_lock because it iterates on
207 * reader threads. */
9598a481 208 force_mb_all_threads();
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209
210 internal_urcu_unlock();
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211}
212
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213void urcu_add_reader(pthread_t id)
214{
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215 struct reader_data *oldarray;
216
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217 if (!reader_data) {
218 alloc_readers = INIT_NUM_THREADS;
f69f195a 219 num_readers = 0;
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220 reader_data =
221 malloc(sizeof(struct reader_data) * alloc_readers);
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222 }
223 if (alloc_readers < num_readers + 1) {
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224 oldarray = reader_data;
225 reader_data = malloc(sizeof(struct reader_data)
226 * (alloc_readers << 1));
227 memcpy(reader_data, oldarray,
228 sizeof(struct reader_data) * alloc_readers);
229 alloc_readers <<= 1;
230 free(oldarray);
231 }
232 reader_data[num_readers].tid = id;
233 /* reference to the TLS of _this_ reader thread. */
1430ee0b 234 reader_data[num_readers].urcu_active_readers = &urcu_active_readers;
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235 num_readers++;
236}
237
238/*
239 * Never shrink (implementation limitation).
240 * This is O(nb threads). Eventually use a hash table.
241 */
242void urcu_remove_reader(pthread_t id)
243{
244 struct reader_data *index;
245
246 assert(reader_data != NULL);
247 for (index = reader_data; index < reader_data + num_readers; index++) {
e6d6e2dc 248 if (pthread_equal(index->tid, id)) {
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249 memcpy(index, &reader_data[num_readers - 1],
250 sizeof(struct reader_data));
251 reader_data[num_readers - 1].tid = 0;
252 reader_data[num_readers - 1].urcu_active_readers = NULL;
253 num_readers--;
254 return;
255 }
256 }
257 /* Hrm not found, forgot to register ? */
258 assert(0);
259}
260
261void urcu_register_thread(void)
262{
c265818b 263 internal_urcu_lock();
41718ff9 264 urcu_add_reader(pthread_self());
c265818b 265 internal_urcu_unlock();
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266}
267
f69f195a 268void urcu_unregister_thread(void)
27b012e2 269{
c265818b 270 internal_urcu_lock();
41718ff9 271 urcu_remove_reader(pthread_self());
c265818b 272 internal_urcu_unlock();
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273}
274
bb488185 275#ifndef DEBUG_FULL_MB
f69f195a 276void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 277{
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278 /*
279 * Executing this smp_mb() is the only purpose of this signal handler.
280 * It punctually promotes barrier() into smp_mb() on every thread it is
281 * executed on.
282 */
b715b99e 283 smp_mb();
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284 atomic_inc(&sig_done);
285}
286
287void __attribute__((constructor)) urcu_init(void)
288{
289 struct sigaction act;
290 int ret;
291
292 act.sa_sigaction = sigurcu_handler;
293 ret = sigaction(SIGURCU, &act, NULL);
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294 if (ret) {
295 perror("Error in sigaction");
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296 exit(-1);
297 }
298}
299
300void __attribute__((destructor)) urcu_exit(void)
301{
302 struct sigaction act;
303 int ret;
304
305 ret = sigaction(SIGURCU, NULL, &act);
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306 if (ret) {
307 perror("Error in sigaction");
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308 exit(-1);
309 }
310 assert(act.sa_sigaction == sigurcu_handler);
311 free(reader_data);
312}
bb488185 313#endif
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