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 | ||
d1238495 PH |
117 | if (rcu_reader_qs_gp & 1) |
118 | rcu_reader_qs_gp = urcu_gp_ctr + 1; | |
119 | ||
9f1621ca MD |
120 | if (!registry) |
121 | return; | |
122 | /* | |
3395d46c | 123 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca MD |
124 | */ |
125 | for (index = registry; index < registry + num_readers; index++) { | |
126 | #ifndef HAS_INCOHERENT_CACHES | |
3395d46c MD |
127 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
128 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) | |
9f1621ca MD |
129 | cpu_relax(); |
130 | #else /* #ifndef HAS_INCOHERENT_CACHES */ | |
131 | int wait_loops = 0; | |
132 | /* | |
133 | * BUSY-LOOP. Force the reader thread to commit its | |
3395d46c | 134 | * rcu_reader_qs_gp update to memory if we wait for too long. |
9f1621ca | 135 | */ |
3395d46c MD |
136 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
137 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { | |
9f1621ca MD |
138 | if (wait_loops++ == KICK_READER_LOOPS) { |
139 | force_mb_single_thread(index); | |
140 | wait_loops = 0; | |
141 | } else { | |
142 | cpu_relax(); | |
143 | } | |
144 | } | |
145 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ | |
146 | } | |
147 | } | |
148 | ||
149 | void synchronize_rcu(void) | |
150 | { | |
ff2f67a0 MD |
151 | int was_online; |
152 | ||
153 | was_online = rcu_reader_qs_gp & 1; | |
154 | ||
155 | /* | |
156 | * Mark the writer thread offline to make sure we don't wait for | |
157 | * our own quiescent state. This allows using synchronize_rcu() in | |
158 | * threads registered as readers. | |
159 | */ | |
160 | if (was_online) | |
161 | _rcu_thread_offline(); | |
162 | ||
9f1621ca MD |
163 | internal_urcu_lock(); |
164 | force_mb_all_threads(); | |
165 | urcu_gp_ctr += 2; | |
166 | wait_for_quiescent_state(); | |
167 | force_mb_all_threads(); | |
168 | internal_urcu_unlock(); | |
ff2f67a0 MD |
169 | |
170 | if (was_online) | |
171 | _rcu_thread_online(); | |
9f1621ca MD |
172 | } |
173 | ||
174 | /* | |
175 | * library wrappers to be used by non-LGPL compatible source code. | |
176 | */ | |
177 | ||
178 | void rcu_read_lock(void) | |
179 | { | |
180 | _rcu_read_lock(); | |
181 | } | |
182 | ||
183 | void rcu_read_unlock(void) | |
184 | { | |
185 | _rcu_read_unlock(); | |
186 | } | |
187 | ||
188 | void *rcu_dereference(void *p) | |
189 | { | |
190 | return _rcu_dereference(p); | |
191 | } | |
192 | ||
193 | void *rcu_assign_pointer_sym(void **p, void *v) | |
194 | { | |
195 | wmb(); | |
196 | return STORE_SHARED(p, v); | |
197 | } | |
198 | ||
199 | void *rcu_xchg_pointer_sym(void **p, void *v) | |
200 | { | |
201 | wmb(); | |
202 | return xchg(p, v); | |
203 | } | |
204 | ||
205 | void *rcu_publish_content_sym(void **p, void *v) | |
206 | { | |
207 | void *oldptr; | |
208 | ||
209 | oldptr = _rcu_xchg_pointer(p, v); | |
210 | synchronize_rcu(); | |
211 | return oldptr; | |
212 | } | |
213 | ||
7ac06cef MD |
214 | void rcu_quiescent_state(void) |
215 | { | |
216 | _rcu_quiescent_state(); | |
217 | } | |
218 | ||
219 | void rcu_thread_offline(void) | |
220 | { | |
221 | _rcu_thread_offline(); | |
222 | } | |
223 | ||
224 | void rcu_thread_online(void) | |
225 | { | |
226 | _rcu_thread_online(); | |
227 | } | |
228 | ||
9f1621ca MD |
229 | static void rcu_add_reader(pthread_t id) |
230 | { | |
231 | struct reader_registry *oldarray; | |
232 | ||
233 | if (!registry) { | |
234 | alloc_readers = INIT_NUM_THREADS; | |
235 | num_readers = 0; | |
236 | registry = | |
237 | malloc(sizeof(struct reader_registry) * alloc_readers); | |
238 | } | |
239 | if (alloc_readers < num_readers + 1) { | |
240 | oldarray = registry; | |
241 | registry = malloc(sizeof(struct reader_registry) | |
242 | * (alloc_readers << 1)); | |
243 | memcpy(registry, oldarray, | |
244 | sizeof(struct reader_registry) * alloc_readers); | |
245 | alloc_readers <<= 1; | |
246 | free(oldarray); | |
247 | } | |
248 | registry[num_readers].tid = id; | |
249 | /* reference to the TLS of _this_ reader thread. */ | |
3395d46c | 250 | registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; |
9f1621ca MD |
251 | num_readers++; |
252 | } | |
253 | ||
254 | /* | |
255 | * Never shrink (implementation limitation). | |
256 | * This is O(nb threads). Eventually use a hash table. | |
257 | */ | |
258 | static void rcu_remove_reader(pthread_t id) | |
259 | { | |
260 | struct reader_registry *index; | |
261 | ||
262 | assert(registry != NULL); | |
263 | for (index = registry; index < registry + num_readers; index++) { | |
264 | if (pthread_equal(index->tid, id)) { | |
265 | memcpy(index, ®istry[num_readers - 1], | |
266 | sizeof(struct reader_registry)); | |
267 | registry[num_readers - 1].tid = 0; | |
3395d46c | 268 | registry[num_readers - 1].rcu_reader_qs_gp = NULL; |
9f1621ca MD |
269 | num_readers--; |
270 | return; | |
271 | } | |
272 | } | |
273 | /* Hrm not found, forgot to register ? */ | |
274 | assert(0); | |
275 | } | |
276 | ||
277 | void rcu_register_thread(void) | |
278 | { | |
279 | internal_urcu_lock(); | |
9f1621ca MD |
280 | rcu_add_reader(pthread_self()); |
281 | internal_urcu_unlock(); | |
5f373c84 | 282 | _rcu_thread_online(); |
9f1621ca MD |
283 | } |
284 | ||
285 | void rcu_unregister_thread(void) | |
286 | { | |
76f3022f MD |
287 | /* |
288 | * We have to make the thread offline otherwise we end up dealocking | |
289 | * with a waiting writer. | |
290 | */ | |
291 | _rcu_thread_offline(); | |
9f1621ca MD |
292 | internal_urcu_lock(); |
293 | rcu_remove_reader(pthread_self()); | |
294 | internal_urcu_unlock(); | |
295 | } |