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9f1621ca MD |
1 | /* |
2 | * urcu.c | |
3 | * | |
4 | * Userspace RCU library | |
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 | ||
3395d46c | 35 | #include "urcu-qsbr.h" |
9f1621ca | 36 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
3395d46c | 37 | //#include "urcu.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 | char *need_mb; |
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; | |
67 | static char __thread need_mb; | |
68 | static int num_readers, alloc_readers; | |
69 | ||
70 | void internal_urcu_lock(void) | |
71 | { | |
72 | int ret; | |
73 | ||
74 | #ifndef DISTRUST_SIGNALS_EXTREME | |
75 | ret = pthread_mutex_lock(&urcu_mutex); | |
76 | if (ret) { | |
77 | perror("Error in pthread mutex lock"); | |
78 | exit(-1); | |
79 | } | |
80 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
81 | while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { | |
82 | if (ret != EBUSY && ret != EINTR) { | |
83 | printf("ret = %d, errno = %d\n", ret, errno); | |
84 | perror("Error in pthread mutex lock"); | |
85 | exit(-1); | |
86 | } | |
87 | if (need_mb) { | |
88 | smp_mb(); | |
89 | need_mb = 0; | |
90 | smp_mb(); | |
91 | } | |
92 | poll(NULL,0,10); | |
93 | } | |
94 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
95 | } | |
96 | ||
97 | void internal_urcu_unlock(void) | |
98 | { | |
99 | int ret; | |
100 | ||
101 | ret = pthread_mutex_unlock(&urcu_mutex); | |
102 | if (ret) { | |
103 | perror("Error in pthread mutex unlock"); | |
104 | exit(-1); | |
105 | } | |
106 | } | |
107 | ||
9f1621ca MD |
108 | #ifdef HAS_INCOHERENT_CACHES |
109 | static void force_mb_single_thread(struct reader_registry *index) | |
110 | { | |
111 | smp_mb(); | |
112 | } | |
113 | #endif /* #ifdef HAS_INCOHERENT_CACHES */ | |
114 | ||
115 | static void force_mb_all_threads(void) | |
116 | { | |
117 | smp_mb(); | |
118 | } | |
9f1621ca MD |
119 | |
120 | void wait_for_quiescent_state(void) | |
121 | { | |
122 | struct reader_registry *index; | |
123 | ||
124 | if (!registry) | |
125 | return; | |
126 | /* | |
3395d46c | 127 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca MD |
128 | */ |
129 | for (index = registry; index < registry + num_readers; index++) { | |
130 | #ifndef HAS_INCOHERENT_CACHES | |
3395d46c MD |
131 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
132 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) | |
9f1621ca MD |
133 | cpu_relax(); |
134 | #else /* #ifndef HAS_INCOHERENT_CACHES */ | |
135 | int wait_loops = 0; | |
136 | /* | |
137 | * BUSY-LOOP. Force the reader thread to commit its | |
3395d46c | 138 | * rcu_reader_qs_gp update to memory if we wait for too long. |
9f1621ca | 139 | */ |
3395d46c MD |
140 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && |
141 | (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { | |
9f1621ca MD |
142 | if (wait_loops++ == KICK_READER_LOOPS) { |
143 | force_mb_single_thread(index); | |
144 | wait_loops = 0; | |
145 | } else { | |
146 | cpu_relax(); | |
147 | } | |
148 | } | |
149 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ | |
150 | } | |
151 | } | |
152 | ||
153 | void synchronize_rcu(void) | |
154 | { | |
155 | internal_urcu_lock(); | |
156 | force_mb_all_threads(); | |
157 | urcu_gp_ctr += 2; | |
158 | wait_for_quiescent_state(); | |
159 | force_mb_all_threads(); | |
160 | internal_urcu_unlock(); | |
161 | } | |
162 | ||
163 | /* | |
164 | * library wrappers to be used by non-LGPL compatible source code. | |
165 | */ | |
166 | ||
167 | void rcu_read_lock(void) | |
168 | { | |
169 | _rcu_read_lock(); | |
170 | } | |
171 | ||
172 | void rcu_read_unlock(void) | |
173 | { | |
174 | _rcu_read_unlock(); | |
175 | } | |
176 | ||
177 | void *rcu_dereference(void *p) | |
178 | { | |
179 | return _rcu_dereference(p); | |
180 | } | |
181 | ||
182 | void *rcu_assign_pointer_sym(void **p, void *v) | |
183 | { | |
184 | wmb(); | |
185 | return STORE_SHARED(p, v); | |
186 | } | |
187 | ||
188 | void *rcu_xchg_pointer_sym(void **p, void *v) | |
189 | { | |
190 | wmb(); | |
191 | return xchg(p, v); | |
192 | } | |
193 | ||
194 | void *rcu_publish_content_sym(void **p, void *v) | |
195 | { | |
196 | void *oldptr; | |
197 | ||
198 | oldptr = _rcu_xchg_pointer(p, v); | |
199 | synchronize_rcu(); | |
200 | return oldptr; | |
201 | } | |
202 | ||
203 | static void rcu_add_reader(pthread_t id) | |
204 | { | |
205 | struct reader_registry *oldarray; | |
206 | ||
207 | if (!registry) { | |
208 | alloc_readers = INIT_NUM_THREADS; | |
209 | num_readers = 0; | |
210 | registry = | |
211 | malloc(sizeof(struct reader_registry) * alloc_readers); | |
212 | } | |
213 | if (alloc_readers < num_readers + 1) { | |
214 | oldarray = registry; | |
215 | registry = malloc(sizeof(struct reader_registry) | |
216 | * (alloc_readers << 1)); | |
217 | memcpy(registry, oldarray, | |
218 | sizeof(struct reader_registry) * alloc_readers); | |
219 | alloc_readers <<= 1; | |
220 | free(oldarray); | |
221 | } | |
222 | registry[num_readers].tid = id; | |
223 | /* reference to the TLS of _this_ reader thread. */ | |
3395d46c | 224 | registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; |
9f1621ca MD |
225 | registry[num_readers].need_mb = &need_mb; |
226 | num_readers++; | |
227 | } | |
228 | ||
229 | /* | |
230 | * Never shrink (implementation limitation). | |
231 | * This is O(nb threads). Eventually use a hash table. | |
232 | */ | |
233 | static void rcu_remove_reader(pthread_t id) | |
234 | { | |
235 | struct reader_registry *index; | |
236 | ||
237 | assert(registry != NULL); | |
238 | for (index = registry; index < registry + num_readers; index++) { | |
239 | if (pthread_equal(index->tid, id)) { | |
240 | memcpy(index, ®istry[num_readers - 1], | |
241 | sizeof(struct reader_registry)); | |
242 | registry[num_readers - 1].tid = 0; | |
3395d46c | 243 | registry[num_readers - 1].rcu_reader_qs_gp = NULL; |
9f1621ca MD |
244 | num_readers--; |
245 | return; | |
246 | } | |
247 | } | |
248 | /* Hrm not found, forgot to register ? */ | |
249 | assert(0); | |
250 | } | |
251 | ||
252 | void rcu_register_thread(void) | |
253 | { | |
254 | internal_urcu_lock(); | |
9f1621ca MD |
255 | rcu_add_reader(pthread_self()); |
256 | internal_urcu_unlock(); | |
257 | } | |
258 | ||
259 | void rcu_unregister_thread(void) | |
260 | { | |
76f3022f MD |
261 | /* |
262 | * We have to make the thread offline otherwise we end up dealocking | |
263 | * with a waiting writer. | |
264 | */ | |
265 | _rcu_thread_offline(); | |
9f1621ca MD |
266 | internal_urcu_lock(); |
267 | rcu_remove_reader(pthread_self()); | |
268 | internal_urcu_unlock(); | |
269 | } |