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 | ||
727f819d | 35 | #define BUILD_QSBR_LIB |
7ac06cef | 36 | #include "urcu-qsbr-static.h" |
9f1621ca | 37 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
7ac06cef | 38 | #include "urcu-qsbr.h" |
9f1621ca | 39 | |
9f1621ca MD |
40 | pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; |
41 | ||
42 | /* | |
43 | * Global grace period counter. | |
44 | */ | |
ac258107 | 45 | unsigned long urcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca MD |
46 | |
47 | /* | |
48 | * Written to only by each individual reader. Read by both the reader and the | |
49 | * writers. | |
50 | */ | |
f0f7dbdd | 51 | unsigned long __thread rcu_reader_qs_gp; |
9f1621ca MD |
52 | |
53 | /* Thread IDs of registered readers */ | |
54 | #define INIT_NUM_THREADS 4 | |
55 | ||
56 | struct reader_registry { | |
57 | pthread_t tid; | |
f0f7dbdd | 58 | unsigned long *rcu_reader_qs_gp; |
9f1621ca MD |
59 | }; |
60 | ||
61 | #ifdef DEBUG_YIELD | |
62 | unsigned int yield_active; | |
63 | unsigned int __thread rand_yield; | |
64 | #endif | |
65 | ||
66 | static struct reader_registry *registry; | |
9f1621ca MD |
67 | static int num_readers, alloc_readers; |
68 | ||
90c1618a | 69 | static void internal_urcu_lock(void) |
9f1621ca MD |
70 | { |
71 | int ret; | |
72 | ||
73 | #ifndef DISTRUST_SIGNALS_EXTREME | |
74 | ret = pthread_mutex_lock(&urcu_mutex); | |
75 | if (ret) { | |
76 | perror("Error in pthread mutex lock"); | |
77 | exit(-1); | |
78 | } | |
79 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
80 | while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { | |
81 | if (ret != EBUSY && ret != EINTR) { | |
82 | printf("ret = %d, errno = %d\n", ret, errno); | |
83 | perror("Error in pthread mutex lock"); | |
84 | exit(-1); | |
85 | } | |
9f1621ca MD |
86 | poll(NULL,0,10); |
87 | } | |
88 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
89 | } | |
90 | ||
90c1618a | 91 | static void internal_urcu_unlock(void) |
9f1621ca MD |
92 | { |
93 | int ret; | |
94 | ||
95 | ret = pthread_mutex_unlock(&urcu_mutex); | |
96 | if (ret) { | |
97 | perror("Error in pthread mutex unlock"); | |
98 | exit(-1); | |
99 | } | |
100 | } | |
101 | ||
9f1621ca MD |
102 | #ifdef HAS_INCOHERENT_CACHES |
103 | static void force_mb_single_thread(struct reader_registry *index) | |
104 | { | |
105 | smp_mb(); | |
106 | } | |
107 | #endif /* #ifdef HAS_INCOHERENT_CACHES */ | |
108 | ||
90c1618a | 109 | static void wait_for_quiescent_state(void) |
9f1621ca MD |
110 | { |
111 | struct reader_registry *index; | |
112 | ||
113 | if (!registry) | |
114 | return; | |
115 | /* | |
3395d46c | 116 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca MD |
117 | */ |
118 | for (index = registry; index < registry + num_readers; index++) { | |
119 | #ifndef HAS_INCOHERENT_CACHES | |
4e560c17 | 120 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) |
9f1621ca MD |
121 | cpu_relax(); |
122 | #else /* #ifndef HAS_INCOHERENT_CACHES */ | |
123 | int wait_loops = 0; | |
124 | /* | |
125 | * BUSY-LOOP. Force the reader thread to commit its | |
3395d46c | 126 | * rcu_reader_qs_gp update to memory if we wait for too long. |
9f1621ca | 127 | */ |
4e560c17 | 128 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) { |
9f1621ca MD |
129 | if (wait_loops++ == KICK_READER_LOOPS) { |
130 | force_mb_single_thread(index); | |
131 | wait_loops = 0; | |
132 | } else { | |
133 | cpu_relax(); | |
134 | } | |
135 | } | |
136 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ | |
137 | } | |
138 | } | |
139 | ||
140 | void synchronize_rcu(void) | |
141 | { | |
f0f7dbdd | 142 | unsigned long was_online; |
ff2f67a0 | 143 | |
ab179a17 | 144 | was_online = rcu_reader_qs_gp; |
ff2f67a0 MD |
145 | |
146 | /* | |
147 | * Mark the writer thread offline to make sure we don't wait for | |
148 | * our own quiescent state. This allows using synchronize_rcu() in | |
149 | * threads registered as readers. | |
150 | */ | |
8f50d1ce | 151 | smp_mb(); |
ff2f67a0 | 152 | if (was_online) |
8f50d1ce | 153 | STORE_SHARED(rcu_reader_qs_gp, 0); |
ff2f67a0 | 154 | |
4e27f058 | 155 | internal_urcu_lock(); |
55570466 | 156 | STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); |
9f1621ca | 157 | wait_for_quiescent_state(); |
9f1621ca | 158 | internal_urcu_unlock(); |
ff2f67a0 MD |
159 | |
160 | if (was_online) | |
ab179a17 | 161 | _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); |
8f50d1ce | 162 | smp_mb(); |
9f1621ca MD |
163 | } |
164 | ||
165 | /* | |
166 | * library wrappers to be used by non-LGPL compatible source code. | |
167 | */ | |
168 | ||
169 | void rcu_read_lock(void) | |
170 | { | |
171 | _rcu_read_lock(); | |
172 | } | |
173 | ||
174 | void rcu_read_unlock(void) | |
175 | { | |
176 | _rcu_read_unlock(); | |
177 | } | |
178 | ||
179 | void *rcu_dereference(void *p) | |
180 | { | |
181 | return _rcu_dereference(p); | |
182 | } | |
183 | ||
184 | void *rcu_assign_pointer_sym(void **p, void *v) | |
185 | { | |
186 | wmb(); | |
187 | return STORE_SHARED(p, v); | |
188 | } | |
189 | ||
190 | void *rcu_xchg_pointer_sym(void **p, void *v) | |
191 | { | |
192 | wmb(); | |
193 | return xchg(p, v); | |
194 | } | |
195 | ||
196 | void *rcu_publish_content_sym(void **p, void *v) | |
197 | { | |
198 | void *oldptr; | |
199 | ||
200 | oldptr = _rcu_xchg_pointer(p, v); | |
201 | synchronize_rcu(); | |
202 | return oldptr; | |
203 | } | |
204 | ||
7ac06cef MD |
205 | void rcu_quiescent_state(void) |
206 | { | |
207 | _rcu_quiescent_state(); | |
208 | } | |
209 | ||
210 | void rcu_thread_offline(void) | |
211 | { | |
212 | _rcu_thread_offline(); | |
213 | } | |
214 | ||
215 | void rcu_thread_online(void) | |
216 | { | |
217 | _rcu_thread_online(); | |
218 | } | |
219 | ||
9f1621ca MD |
220 | static void rcu_add_reader(pthread_t id) |
221 | { | |
222 | struct reader_registry *oldarray; | |
223 | ||
224 | if (!registry) { | |
225 | alloc_readers = INIT_NUM_THREADS; | |
226 | num_readers = 0; | |
227 | registry = | |
228 | malloc(sizeof(struct reader_registry) * alloc_readers); | |
229 | } | |
230 | if (alloc_readers < num_readers + 1) { | |
231 | oldarray = registry; | |
232 | registry = malloc(sizeof(struct reader_registry) | |
233 | * (alloc_readers << 1)); | |
234 | memcpy(registry, oldarray, | |
235 | sizeof(struct reader_registry) * alloc_readers); | |
236 | alloc_readers <<= 1; | |
237 | free(oldarray); | |
238 | } | |
239 | registry[num_readers].tid = id; | |
240 | /* reference to the TLS of _this_ reader thread. */ | |
3395d46c | 241 | registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; |
9f1621ca MD |
242 | num_readers++; |
243 | } | |
244 | ||
245 | /* | |
246 | * Never shrink (implementation limitation). | |
247 | * This is O(nb threads). Eventually use a hash table. | |
248 | */ | |
249 | static void rcu_remove_reader(pthread_t id) | |
250 | { | |
251 | struct reader_registry *index; | |
252 | ||
253 | assert(registry != NULL); | |
254 | for (index = registry; index < registry + num_readers; index++) { | |
255 | if (pthread_equal(index->tid, id)) { | |
256 | memcpy(index, ®istry[num_readers - 1], | |
257 | sizeof(struct reader_registry)); | |
258 | registry[num_readers - 1].tid = 0; | |
3395d46c | 259 | registry[num_readers - 1].rcu_reader_qs_gp = NULL; |
9f1621ca MD |
260 | num_readers--; |
261 | return; | |
262 | } | |
263 | } | |
264 | /* Hrm not found, forgot to register ? */ | |
265 | assert(0); | |
266 | } | |
267 | ||
268 | void rcu_register_thread(void) | |
269 | { | |
270 | internal_urcu_lock(); | |
9f1621ca MD |
271 | rcu_add_reader(pthread_self()); |
272 | internal_urcu_unlock(); | |
5f373c84 | 273 | _rcu_thread_online(); |
9f1621ca MD |
274 | } |
275 | ||
276 | void rcu_unregister_thread(void) | |
277 | { | |
76f3022f MD |
278 | /* |
279 | * We have to make the thread offline otherwise we end up dealocking | |
280 | * with a waiting writer. | |
281 | */ | |
282 | _rcu_thread_offline(); | |
9f1621ca MD |
283 | internal_urcu_lock(); |
284 | rcu_remove_reader(pthread_self()); | |
285 | internal_urcu_unlock(); | |
286 | } |