Commit | Line | Data |
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9f1621ca | 1 | /* |
7ac06cef | 2 | * urcu-qsbr.c |
9f1621ca | 3 | * |
7ac06cef | 4 | * Userspace RCU QSBR library |
9f1621ca MD |
5 | * |
6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | |
7 | * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. | |
8 | * | |
9 | * This library is free software; you can redistribute it and/or | |
10 | * modify it under the terms of the GNU Lesser General Public | |
11 | * License as published by the Free Software Foundation; either | |
12 | * version 2.1 of the License, or (at your option) any later version. | |
13 | * | |
14 | * This library is distributed in the hope that it will be useful, | |
15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
17 | * Lesser General Public License for more details. | |
18 | * | |
19 | * You should have received a copy of the GNU Lesser General Public | |
20 | * License along with this library; if not, write to the Free Software | |
21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
22 | * | |
23 | * IBM's contributions to this file may be relicensed under LGPLv2 or later. | |
24 | */ | |
25 | ||
26 | #include <stdio.h> | |
27 | #include <pthread.h> | |
28 | #include <signal.h> | |
29 | #include <assert.h> | |
30 | #include <stdlib.h> | |
31 | #include <string.h> | |
32 | #include <errno.h> | |
33 | #include <poll.h> | |
34 | ||
7ac06cef | 35 | #include "urcu-qsbr-static.h" |
9f1621ca | 36 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
7ac06cef | 37 | #include "urcu-qsbr.h" |
9f1621ca | 38 | |
9f1621ca MD |
39 | pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; |
40 | ||
41 | /* | |
42 | * Global grace period counter. | |
43 | */ | |
44 | long urcu_gp_ctr = 0; | |
45 | ||
46 | /* | |
47 | * Written to only by each individual reader. Read by both the reader and the | |
48 | * writers. | |
49 | */ | |
3395d46c | 50 | long __thread rcu_reader_qs_gp; |
9f1621ca MD |
51 | |
52 | /* Thread IDs of registered readers */ | |
53 | #define INIT_NUM_THREADS 4 | |
54 | ||
55 | struct reader_registry { | |
56 | pthread_t tid; | |
3395d46c | 57 | long *rcu_reader_qs_gp; |
9f1621ca MD |
58 | }; |
59 | ||
60 | #ifdef DEBUG_YIELD | |
61 | unsigned int yield_active; | |
62 | unsigned int __thread rand_yield; | |
63 | #endif | |
64 | ||
65 | static struct reader_registry *registry; | |
9f1621ca MD |
66 | static int num_readers, alloc_readers; |
67 | ||
90c1618a | 68 | static void internal_urcu_lock(void) |
9f1621ca MD |
69 | { |
70 | int ret; | |
71 | ||
72 | #ifndef DISTRUST_SIGNALS_EXTREME | |
73 | ret = pthread_mutex_lock(&urcu_mutex); | |
74 | if (ret) { | |
75 | perror("Error in pthread mutex lock"); | |
76 | exit(-1); | |
77 | } | |
78 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
79 | while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { | |
80 | if (ret != EBUSY && ret != EINTR) { | |
81 | printf("ret = %d, errno = %d\n", ret, errno); | |
82 | perror("Error in pthread mutex lock"); | |
83 | exit(-1); | |
84 | } | |
9f1621ca MD |
85 | poll(NULL,0,10); |
86 | } | |
87 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
88 | } | |
89 | ||
90c1618a | 90 | static void internal_urcu_unlock(void) |
9f1621ca MD |
91 | { |
92 | int ret; | |
93 | ||
94 | ret = pthread_mutex_unlock(&urcu_mutex); | |
95 | if (ret) { | |
96 | perror("Error in pthread mutex unlock"); | |
97 | exit(-1); | |
98 | } | |
99 | } | |
100 | ||
9f1621ca MD |
101 | #ifdef HAS_INCOHERENT_CACHES |
102 | static void force_mb_single_thread(struct reader_registry *index) | |
103 | { | |
104 | smp_mb(); | |
105 | } | |
106 | #endif /* #ifdef HAS_INCOHERENT_CACHES */ | |
107 | ||
108 | static void force_mb_all_threads(void) | |
109 | { | |
110 | smp_mb(); | |
111 | } | |
9f1621ca | 112 | |
90c1618a | 113 | static void wait_for_quiescent_state(void) |
9f1621ca MD |
114 | { |
115 | struct reader_registry *index; | |
116 | ||
117 | if (!registry) | |
118 | return; | |
119 | /* | |
3395d46c | 120 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca MD |
121 | */ |
122 | for (index = registry; index < registry + num_readers; index++) { | |
123 | #ifndef HAS_INCOHERENT_CACHES | |
3395d46c MD |
124 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
125 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) | |
9f1621ca MD |
126 | cpu_relax(); |
127 | #else /* #ifndef HAS_INCOHERENT_CACHES */ | |
128 | int wait_loops = 0; | |
129 | /* | |
130 | * BUSY-LOOP. Force the reader thread to commit its | |
3395d46c | 131 | * rcu_reader_qs_gp update to memory if we wait for too long. |
9f1621ca | 132 | */ |
3395d46c MD |
133 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
134 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { | |
9f1621ca MD |
135 | if (wait_loops++ == KICK_READER_LOOPS) { |
136 | force_mb_single_thread(index); | |
137 | wait_loops = 0; | |
138 | } else { | |
139 | cpu_relax(); | |
140 | } | |
141 | } | |
142 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ | |
143 | } | |
144 | } | |
145 | ||
146 | void synchronize_rcu(void) | |
147 | { | |
ff2f67a0 MD |
148 | int was_online; |
149 | ||
150 | was_online = rcu_reader_qs_gp & 1; | |
151 | ||
152 | /* | |
153 | * Mark the writer thread offline to make sure we don't wait for | |
154 | * our own quiescent state. This allows using synchronize_rcu() in | |
155 | * threads registered as readers. | |
156 | */ | |
157 | if (was_online) | |
158 | _rcu_thread_offline(); | |
159 | ||
9f1621ca MD |
160 | internal_urcu_lock(); |
161 | force_mb_all_threads(); | |
162 | urcu_gp_ctr += 2; | |
163 | wait_for_quiescent_state(); | |
164 | force_mb_all_threads(); | |
165 | internal_urcu_unlock(); | |
ff2f67a0 MD |
166 | |
167 | if (was_online) | |
168 | _rcu_thread_online(); | |
9f1621ca MD |
169 | } |
170 | ||
171 | /* | |
172 | * library wrappers to be used by non-LGPL compatible source code. | |
173 | */ | |
174 | ||
175 | void rcu_read_lock(void) | |
176 | { | |
177 | _rcu_read_lock(); | |
178 | } | |
179 | ||
180 | void rcu_read_unlock(void) | |
181 | { | |
182 | _rcu_read_unlock(); | |
183 | } | |
184 | ||
185 | void *rcu_dereference(void *p) | |
186 | { | |
187 | return _rcu_dereference(p); | |
188 | } | |
189 | ||
190 | void *rcu_assign_pointer_sym(void **p, void *v) | |
191 | { | |
192 | wmb(); | |
193 | return STORE_SHARED(p, v); | |
194 | } | |
195 | ||
196 | void *rcu_xchg_pointer_sym(void **p, void *v) | |
197 | { | |
198 | wmb(); | |
199 | return xchg(p, v); | |
200 | } | |
201 | ||
202 | void *rcu_publish_content_sym(void **p, void *v) | |
203 | { | |
204 | void *oldptr; | |
205 | ||
206 | oldptr = _rcu_xchg_pointer(p, v); | |
207 | synchronize_rcu(); | |
208 | return oldptr; | |
209 | } | |
210 | ||
7ac06cef MD |
211 | void rcu_quiescent_state(void) |
212 | { | |
213 | _rcu_quiescent_state(); | |
214 | } | |
215 | ||
216 | void rcu_thread_offline(void) | |
217 | { | |
218 | _rcu_thread_offline(); | |
219 | } | |
220 | ||
221 | void rcu_thread_online(void) | |
222 | { | |
223 | _rcu_thread_online(); | |
224 | } | |
225 | ||
9f1621ca MD |
226 | static void rcu_add_reader(pthread_t id) |
227 | { | |
228 | struct reader_registry *oldarray; | |
229 | ||
230 | if (!registry) { | |
231 | alloc_readers = INIT_NUM_THREADS; | |
232 | num_readers = 0; | |
233 | registry = | |
234 | malloc(sizeof(struct reader_registry) * alloc_readers); | |
235 | } | |
236 | if (alloc_readers < num_readers + 1) { | |
237 | oldarray = registry; | |
238 | registry = malloc(sizeof(struct reader_registry) | |
239 | * (alloc_readers << 1)); | |
240 | memcpy(registry, oldarray, | |
241 | sizeof(struct reader_registry) * alloc_readers); | |
242 | alloc_readers <<= 1; | |
243 | free(oldarray); | |
244 | } | |
245 | registry[num_readers].tid = id; | |
246 | /* reference to the TLS of _this_ reader thread. */ | |
3395d46c | 247 | registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; |
9f1621ca MD |
248 | num_readers++; |
249 | } | |
250 | ||
251 | /* | |
252 | * Never shrink (implementation limitation). | |
253 | * This is O(nb threads). Eventually use a hash table. | |
254 | */ | |
255 | static void rcu_remove_reader(pthread_t id) | |
256 | { | |
257 | struct reader_registry *index; | |
258 | ||
259 | assert(registry != NULL); | |
260 | for (index = registry; index < registry + num_readers; index++) { | |
261 | if (pthread_equal(index->tid, id)) { | |
262 | memcpy(index, ®istry[num_readers - 1], | |
263 | sizeof(struct reader_registry)); | |
264 | registry[num_readers - 1].tid = 0; | |
3395d46c | 265 | registry[num_readers - 1].rcu_reader_qs_gp = NULL; |
9f1621ca MD |
266 | num_readers--; |
267 | return; | |
268 | } | |
269 | } | |
270 | /* Hrm not found, forgot to register ? */ | |
271 | assert(0); | |
272 | } | |
273 | ||
274 | void rcu_register_thread(void) | |
275 | { | |
276 | internal_urcu_lock(); | |
9f1621ca MD |
277 | rcu_add_reader(pthread_self()); |
278 | internal_urcu_unlock(); | |
5f373c84 | 279 | _rcu_thread_online(); |
9f1621ca MD |
280 | } |
281 | ||
282 | void rcu_unregister_thread(void) | |
283 | { | |
76f3022f MD |
284 | /* |
285 | * We have to make the thread offline otherwise we end up dealocking | |
286 | * with a waiting writer. | |
287 | */ | |
288 | _rcu_thread_offline(); | |
9f1621ca MD |
289 | internal_urcu_lock(); |
290 | rcu_remove_reader(pthread_self()); | |
291 | internal_urcu_unlock(); | |
292 | } |