Commit | Line | Data |
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b257a10b MD |
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 | ||
27b012e2 MD |
11 | #include <stdio.h> |
12 | #include <pthread.h> | |
13 | #include <signal.h> | |
14 | #include <assert.h> | |
f69f195a MD |
15 | #include <stdlib.h> |
16 | #include <string.h> | |
27b012e2 MD |
17 | |
18 | #include "urcu.h" | |
19 | ||
20 | pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; | |
21 | ||
128166c9 MD |
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 | */ | |
27 | long urcu_gp_ctr = RCU_GP_COUNT; | |
27b012e2 | 28 | |
6e8b8429 | 29 | long __thread urcu_active_readers; |
27b012e2 MD |
30 | |
31 | /* Thread IDs of registered readers */ | |
32 | #define INIT_NUM_THREADS 4 | |
33 | ||
34 | struct reader_data { | |
35 | pthread_t tid; | |
128166c9 | 36 | long *urcu_active_readers; |
27b012e2 MD |
37 | }; |
38 | ||
cf380c2f | 39 | #ifdef DEBUG_YIELD |
9d335088 MD |
40 | unsigned int yield_active; |
41 | unsigned int __thread rand_yield; | |
cf380c2f MD |
42 | #endif |
43 | ||
27b012e2 MD |
44 | static struct reader_data *reader_data; |
45 | static int num_readers, alloc_readers; | |
b715b99e | 46 | #ifndef DEBUG_FULL_MB |
27b012e2 | 47 | static int sig_done; |
b715b99e | 48 | #endif |
27b012e2 | 49 | |
c265818b | 50 | void internal_urcu_lock(void) |
41718ff9 MD |
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 | 60 | void internal_urcu_unlock(void) |
41718ff9 MD |
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 | ||
27b012e2 MD |
71 | /* |
72 | * called with urcu_mutex held. | |
73 | */ | |
1430ee0b | 74 | static void switch_next_urcu_qparity(void) |
27b012e2 | 75 | { |
1430ee0b | 76 | urcu_gp_ctr ^= RCU_GP_CTR_BIT; |
27b012e2 MD |
77 | } |
78 | ||
bb488185 | 79 | #ifdef DEBUG_FULL_MB |
40e140c9 MD |
80 | static void force_mb_single_thread(pthread_t tid) |
81 | { | |
82 | smp_mb(); | |
83 | } | |
84 | ||
bb488185 MD |
85 | static void force_mb_all_threads(void) |
86 | { | |
b715b99e | 87 | smp_mb(); |
bb488185 MD |
88 | } |
89 | #else | |
40e140c9 MD |
90 | |
91 | static 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 | */ | |
3a86deba MD |
101 | while (LOAD_REMOTE(sig_done) < 1) |
102 | cpu_relax(); | |
40e140c9 MD |
103 | smp_mb(); /* read sig_done before ending the barrier */ |
104 | } | |
105 | ||
27b012e2 MD |
106 | static 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 |
27b012e2 MD |
111 | * compiler barriers around rcu read lock as real memory barriers. |
112 | */ | |
113 | if (!reader_data) | |
114 | return; | |
27b012e2 | 115 | sig_done = 0; |
3a86deba MD |
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); |
27b012e2 MD |
123 | /* |
124 | * Wait for sighandler (and thus mb()) to execute on every thread. | |
125 | * BUSY-LOOP. | |
126 | */ | |
3a86deba MD |
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 | 133 | void wait_for_quiescent_state(void) |
27b012e2 | 134 | { |
f69f195a | 135 | struct reader_data *index; |
27b012e2 MD |
136 | |
137 | if (!reader_data) | |
138 | return; | |
40e140c9 MD |
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 | /* |
40e140c9 MD |
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 | */ |
40e140c9 MD |
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 | } |
27b012e2 MD |
155 | } |
156 | ||
9598a481 | 157 | void synchronize_rcu(void) |
2bc59bd7 | 158 | { |
135530fd MD |
159 | internal_urcu_lock(); |
160 | ||
9598a481 | 161 | /* All threads should read qparity before accessing data structure |
135530fd MD |
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 */ |
2bc59bd7 PM |
168 | |
169 | /* | |
9598a481 MD |
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 | |
9598a481 MD |
177 | /* |
178 | * Wait for previous parity to be empty of readers. | |
179 | */ | |
180 | wait_for_quiescent_state(); /* Wait readers in parity 0 */ | |
9598a481 MD |
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(); |
9598a481 MD |
189 | |
190 | switch_next_urcu_qparity(); /* 1 -> 0 */ | |
9598a481 MD |
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(); |
9598a481 MD |
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 |
135530fd MD |
206 | * freed. Must be done within internal_urcu_lock because it iterates on |
207 | * reader threads. */ | |
9598a481 | 208 | force_mb_all_threads(); |
135530fd MD |
209 | |
210 | internal_urcu_unlock(); | |
2bc59bd7 PM |
211 | } |
212 | ||
27b012e2 MD |
213 | void urcu_add_reader(pthread_t id) |
214 | { | |
f69f195a MD |
215 | struct reader_data *oldarray; |
216 | ||
27b012e2 MD |
217 | if (!reader_data) { |
218 | alloc_readers = INIT_NUM_THREADS; | |
f69f195a | 219 | num_readers = 0; |
27b012e2 MD |
220 | reader_data = |
221 | malloc(sizeof(struct reader_data) * alloc_readers); | |
27b012e2 MD |
222 | } |
223 | if (alloc_readers < num_readers + 1) { | |
27b012e2 MD |
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; |
27b012e2 MD |
235 | num_readers++; |
236 | } | |
237 | ||
238 | /* | |
239 | * Never shrink (implementation limitation). | |
240 | * This is O(nb threads). Eventually use a hash table. | |
241 | */ | |
242 | void 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)) { |
27b012e2 MD |
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 | ||
261 | void urcu_register_thread(void) | |
262 | { | |
c265818b | 263 | internal_urcu_lock(); |
41718ff9 | 264 | urcu_add_reader(pthread_self()); |
c265818b | 265 | internal_urcu_unlock(); |
27b012e2 MD |
266 | } |
267 | ||
f69f195a | 268 | void urcu_unregister_thread(void) |
27b012e2 | 269 | { |
c265818b | 270 | internal_urcu_lock(); |
41718ff9 | 271 | urcu_remove_reader(pthread_self()); |
c265818b | 272 | internal_urcu_unlock(); |
27b012e2 MD |
273 | } |
274 | ||
bb488185 | 275 | #ifndef DEBUG_FULL_MB |
f69f195a | 276 | void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) |
27b012e2 | 277 | { |
40e140c9 MD |
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(); |
27b012e2 MD |
284 | atomic_inc(&sig_done); |
285 | } | |
286 | ||
287 | void __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); | |
f69f195a MD |
294 | if (ret) { |
295 | perror("Error in sigaction"); | |
27b012e2 MD |
296 | exit(-1); |
297 | } | |
298 | } | |
299 | ||
300 | void __attribute__((destructor)) urcu_exit(void) | |
301 | { | |
302 | struct sigaction act; | |
303 | int ret; | |
304 | ||
305 | ret = sigaction(SIGURCU, NULL, &act); | |
f69f195a MD |
306 | if (ret) { |
307 | perror("Error in sigaction"); | |
27b012e2 MD |
308 | exit(-1); |
309 | } | |
310 | assert(act.sa_sigaction == sigurcu_handler); | |
311 | free(reader_data); | |
312 | } | |
bb488185 | 313 | #endif |