Turn *_REMOTE into *_SHARED
[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;
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95 /*
96 * pthread_kill has a smp_mb(). But beware, we assume it performs
97 * a cache flush on architectures with non-coherent cache. Let's play
98 * safe and don't assume anything : we use smp_mc() to make sure the
99 * cache flush is enforced.
100 * smp_mb(); write sig_done before sending the signals
101 */
102 smp_mc(); /* write sig_done before sending the signals */
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103 pthread_kill(tid, SIGURCU);
104 /*
105 * Wait for sighandler (and thus mb()) to execute on every thread.
106 * BUSY-LOOP.
107 */
8895e525 108 while (LOAD_SHARED(sig_done) < 1)
3a86deba 109 cpu_relax();
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110 smp_mb(); /* read sig_done before ending the barrier */
111}
112
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113static void force_mb_all_threads(void)
114{
f69f195a 115 struct reader_data *index;
27b012e2 116 /*
b715b99e 117 * Ask for each threads to execute a smp_mb() so we can consider the
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118 * compiler barriers around rcu read lock as real memory barriers.
119 */
120 if (!reader_data)
121 return;
27b012e2 122 sig_done = 0;
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123 /*
124 * pthread_kill has a smp_mb(). But beware, we assume it performs
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125 * a cache flush on architectures with non-coherent cache. Let's play
126 * safe and don't assume anything : we use smp_mc() to make sure the
127 * cache flush is enforced.
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128 * smp_mb(); write sig_done before sending the signals
129 */
157dca95 130 smp_mc(); /* write sig_done before sending the signals */
ae878d0d 131 for (index = reader_data; index < reader_data + num_readers; index++)
f69f195a 132 pthread_kill(index->tid, SIGURCU);
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133 /*
134 * Wait for sighandler (and thus mb()) to execute on every thread.
135 * BUSY-LOOP.
136 */
8895e525 137 while (LOAD_SHARED(sig_done) < num_readers)
3a86deba 138 cpu_relax();
b715b99e 139 smp_mb(); /* read sig_done before ending the barrier */
27b012e2 140}
bb488185 141#endif
27b012e2 142
1430ee0b 143void wait_for_quiescent_state(void)
27b012e2 144{
f69f195a 145 struct reader_data *index;
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146
147 if (!reader_data)
148 return;
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149 /*
150 * Wait for each thread urcu_active_readers count to become 0.
27b012e2 151 */
f69f195a 152 for (index = reader_data; index < reader_data + num_readers; index++) {
40e140c9 153 int wait_loops = 0;
27b012e2 154 /*
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155 * BUSY-LOOP. Force the reader thread to commit its
156 * urcu_active_readers update to memory if we wait for too long.
27b012e2 157 */
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158 while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
159 if (wait_loops++ == KICK_READER_LOOPS) {
160 force_mb_single_thread(index->tid);
161 wait_loops = 0;
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162 } else {
163 cpu_relax();
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164 }
165 }
27b012e2 166 }
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167}
168
9598a481 169void synchronize_rcu(void)
2bc59bd7 170{
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171 internal_urcu_lock();
172
9598a481 173 /* All threads should read qparity before accessing data structure
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174 * where new ptr points to. Must be done within internal_urcu_lock
175 * because it iterates on reader threads.*/
9598a481 176 /* Write new ptr before changing the qparity */
2bc59bd7 177 force_mb_all_threads();
9598a481 178
9598a481 179 switch_next_urcu_qparity(); /* 0 -> 1 */
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180
181 /*
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182 * Must commit qparity update to memory before waiting for parity
183 * 0 quiescent state. Failure to do so could result in the writer
184 * waiting forever while new readers are always accessing data (no
185 * progress).
2bc59bd7 186 */
3a86deba 187 smp_mc();
2bc59bd7 188
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189 /*
190 * Wait for previous parity to be empty of readers.
191 */
192 wait_for_quiescent_state(); /* Wait readers in parity 0 */
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193
194 /*
195 * Must finish waiting for quiescent state for parity 0 before
196 * committing qparity update to memory. Failure to do so could result in
197 * the writer waiting forever while new readers are always accessing
198 * data (no progress).
199 */
3a86deba 200 smp_mc();
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201
202 switch_next_urcu_qparity(); /* 1 -> 0 */
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203
204 /*
205 * Must commit qparity update to memory before waiting for parity
206 * 1 quiescent state. Failure to do so could result in the writer
207 * waiting forever while new readers are always accessing data (no
208 * progress).
209 */
3a86deba 210 smp_mc();
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211
212 /*
213 * Wait for previous parity to be empty of readers.
214 */
215 wait_for_quiescent_state(); /* Wait readers in parity 1 */
9598a481 216
9598a481 217 /* Finish waiting for reader threads before letting the old ptr being
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218 * freed. Must be done within internal_urcu_lock because it iterates on
219 * reader threads. */
9598a481 220 force_mb_all_threads();
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221
222 internal_urcu_unlock();
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223}
224
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225void urcu_add_reader(pthread_t id)
226{
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227 struct reader_data *oldarray;
228
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229 if (!reader_data) {
230 alloc_readers = INIT_NUM_THREADS;
f69f195a 231 num_readers = 0;
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232 reader_data =
233 malloc(sizeof(struct reader_data) * alloc_readers);
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234 }
235 if (alloc_readers < num_readers + 1) {
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236 oldarray = reader_data;
237 reader_data = malloc(sizeof(struct reader_data)
238 * (alloc_readers << 1));
239 memcpy(reader_data, oldarray,
240 sizeof(struct reader_data) * alloc_readers);
241 alloc_readers <<= 1;
242 free(oldarray);
243 }
244 reader_data[num_readers].tid = id;
245 /* reference to the TLS of _this_ reader thread. */
1430ee0b 246 reader_data[num_readers].urcu_active_readers = &urcu_active_readers;
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247 num_readers++;
248}
249
250/*
251 * Never shrink (implementation limitation).
252 * This is O(nb threads). Eventually use a hash table.
253 */
254void urcu_remove_reader(pthread_t id)
255{
256 struct reader_data *index;
257
258 assert(reader_data != NULL);
259 for (index = reader_data; index < reader_data + num_readers; index++) {
e6d6e2dc 260 if (pthread_equal(index->tid, id)) {
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261 memcpy(index, &reader_data[num_readers - 1],
262 sizeof(struct reader_data));
263 reader_data[num_readers - 1].tid = 0;
264 reader_data[num_readers - 1].urcu_active_readers = NULL;
265 num_readers--;
266 return;
267 }
268 }
269 /* Hrm not found, forgot to register ? */
270 assert(0);
271}
272
273void urcu_register_thread(void)
274{
c265818b 275 internal_urcu_lock();
41718ff9 276 urcu_add_reader(pthread_self());
c265818b 277 internal_urcu_unlock();
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278}
279
f69f195a 280void urcu_unregister_thread(void)
27b012e2 281{
c265818b 282 internal_urcu_lock();
41718ff9 283 urcu_remove_reader(pthread_self());
c265818b 284 internal_urcu_unlock();
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285}
286
bb488185 287#ifndef DEBUG_FULL_MB
f69f195a 288void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 289{
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290 /*
291 * Executing this smp_mb() is the only purpose of this signal handler.
292 * It punctually promotes barrier() into smp_mb() on every thread it is
293 * executed on.
294 */
b715b99e 295 smp_mb();
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296 atomic_inc(&sig_done);
297}
298
299void __attribute__((constructor)) urcu_init(void)
300{
301 struct sigaction act;
302 int ret;
303
304 act.sa_sigaction = sigurcu_handler;
305 ret = sigaction(SIGURCU, &act, NULL);
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306 if (ret) {
307 perror("Error in sigaction");
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308 exit(-1);
309 }
310}
311
312void __attribute__((destructor)) urcu_exit(void)
313{
314 struct sigaction act;
315 int ret;
316
317 ret = sigaction(SIGURCU, NULL, &act);
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318 if (ret) {
319 perror("Error in sigaction");
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320 exit(-1);
321 }
322 assert(act.sa_sigaction == sigurcu_handler);
323 free(reader_data);
324}
bb488185 325#endif
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