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 | ||
90c1618a | 102 | static void wait_for_quiescent_state(void) |
9f1621ca MD |
103 | { |
104 | struct reader_registry *index; | |
105 | ||
106 | if (!registry) | |
107 | return; | |
108 | /* | |
3395d46c | 109 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca MD |
110 | */ |
111 | for (index = registry; index < registry + num_readers; index++) { | |
112 | #ifndef HAS_INCOHERENT_CACHES | |
4e560c17 | 113 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) |
9f1621ca MD |
114 | cpu_relax(); |
115 | #else /* #ifndef HAS_INCOHERENT_CACHES */ | |
47d2f29e MD |
116 | while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) |
117 | smp_mb(); | |
9f1621ca MD |
118 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
119 | } | |
120 | } | |
121 | ||
47d2f29e MD |
122 | /* |
123 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
124 | * long-size to ensure we do not encounter an overflow bug. | |
125 | */ | |
126 | ||
127 | #if (BITS_PER_LONG < 64) | |
128 | /* | |
129 | * called with urcu_mutex held. | |
130 | */ | |
131 | static void switch_next_urcu_qparity(void) | |
132 | { | |
133 | STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR); | |
134 | } | |
135 | ||
136 | void synchronize_rcu(void) | |
137 | { | |
138 | /* All threads should read qparity before accessing data structure | |
139 | * where new ptr points to. | |
140 | */ | |
141 | /* Write new ptr before changing the qparity */ | |
142 | smp_mb(); | |
143 | ||
144 | internal_urcu_lock(); | |
145 | ||
146 | switch_next_urcu_qparity(); /* 0 -> 1 */ | |
147 | ||
148 | /* | |
149 | * Must commit qparity update to memory before waiting for parity | |
150 | * 0 quiescent state. Failure to do so could result in the writer | |
151 | * waiting forever while new readers are always accessing data (no | |
152 | * progress). | |
153 | * Ensured by STORE_SHARED and LOAD_SHARED. | |
154 | */ | |
155 | ||
156 | /* | |
157 | * Wait for previous parity to be empty of readers. | |
158 | */ | |
159 | wait_for_quiescent_state(); /* Wait readers in parity 0 */ | |
160 | ||
161 | /* | |
162 | * Must finish waiting for quiescent state for parity 0 before | |
163 | * committing qparity update to memory. Failure to do so could result in | |
164 | * the writer waiting forever while new readers are always accessing | |
165 | * data (no progress). | |
166 | * Ensured by STORE_SHARED and LOAD_SHARED. | |
167 | */ | |
168 | ||
169 | switch_next_urcu_qparity(); /* 1 -> 0 */ | |
170 | ||
171 | /* | |
172 | * Must commit qparity update to memory before waiting for parity | |
173 | * 1 quiescent state. Failure to do so could result in the writer | |
174 | * waiting forever while new readers are always accessing data (no | |
175 | * progress). | |
176 | * Ensured by STORE_SHARED and LOAD_SHARED. | |
177 | */ | |
178 | ||
179 | /* | |
180 | * Wait for previous parity to be empty of readers. | |
181 | */ | |
182 | wait_for_quiescent_state(); /* Wait readers in parity 1 */ | |
183 | ||
184 | internal_urcu_unlock(); | |
185 | ||
186 | /* Finish waiting for reader threads before letting the old ptr being | |
187 | * freed. | |
188 | */ | |
189 | smp_mb(); | |
190 | } | |
191 | #else /* !(BITS_PER_LONG < 64) */ | |
9f1621ca MD |
192 | void synchronize_rcu(void) |
193 | { | |
f0f7dbdd | 194 | unsigned long was_online; |
ff2f67a0 | 195 | |
ab179a17 | 196 | was_online = rcu_reader_qs_gp; |
ff2f67a0 MD |
197 | |
198 | /* | |
199 | * Mark the writer thread offline to make sure we don't wait for | |
200 | * our own quiescent state. This allows using synchronize_rcu() in | |
201 | * threads registered as readers. | |
202 | */ | |
8f50d1ce | 203 | smp_mb(); |
ff2f67a0 | 204 | if (was_online) |
8f50d1ce | 205 | STORE_SHARED(rcu_reader_qs_gp, 0); |
ff2f67a0 | 206 | |
4e27f058 | 207 | internal_urcu_lock(); |
55570466 | 208 | STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); |
9f1621ca | 209 | wait_for_quiescent_state(); |
9f1621ca | 210 | internal_urcu_unlock(); |
ff2f67a0 MD |
211 | |
212 | if (was_online) | |
ab179a17 | 213 | _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); |
8f50d1ce | 214 | smp_mb(); |
9f1621ca | 215 | } |
47d2f29e | 216 | #endif /* !(BITS_PER_LONG < 64) */ |
9f1621ca MD |
217 | |
218 | /* | |
219 | * library wrappers to be used by non-LGPL compatible source code. | |
220 | */ | |
221 | ||
222 | void rcu_read_lock(void) | |
223 | { | |
224 | _rcu_read_lock(); | |
225 | } | |
226 | ||
227 | void rcu_read_unlock(void) | |
228 | { | |
229 | _rcu_read_unlock(); | |
230 | } | |
231 | ||
232 | void *rcu_dereference(void *p) | |
233 | { | |
234 | return _rcu_dereference(p); | |
235 | } | |
236 | ||
237 | void *rcu_assign_pointer_sym(void **p, void *v) | |
238 | { | |
239 | wmb(); | |
240 | return STORE_SHARED(p, v); | |
241 | } | |
242 | ||
243 | void *rcu_xchg_pointer_sym(void **p, void *v) | |
244 | { | |
245 | wmb(); | |
246 | return xchg(p, v); | |
247 | } | |
248 | ||
249 | void *rcu_publish_content_sym(void **p, void *v) | |
250 | { | |
251 | void *oldptr; | |
252 | ||
253 | oldptr = _rcu_xchg_pointer(p, v); | |
254 | synchronize_rcu(); | |
255 | return oldptr; | |
256 | } | |
257 | ||
7ac06cef MD |
258 | void rcu_quiescent_state(void) |
259 | { | |
260 | _rcu_quiescent_state(); | |
261 | } | |
262 | ||
263 | void rcu_thread_offline(void) | |
264 | { | |
265 | _rcu_thread_offline(); | |
266 | } | |
267 | ||
268 | void rcu_thread_online(void) | |
269 | { | |
270 | _rcu_thread_online(); | |
271 | } | |
272 | ||
9f1621ca MD |
273 | static void rcu_add_reader(pthread_t id) |
274 | { | |
275 | struct reader_registry *oldarray; | |
276 | ||
277 | if (!registry) { | |
278 | alloc_readers = INIT_NUM_THREADS; | |
279 | num_readers = 0; | |
280 | registry = | |
281 | malloc(sizeof(struct reader_registry) * alloc_readers); | |
282 | } | |
283 | if (alloc_readers < num_readers + 1) { | |
284 | oldarray = registry; | |
285 | registry = malloc(sizeof(struct reader_registry) | |
286 | * (alloc_readers << 1)); | |
287 | memcpy(registry, oldarray, | |
288 | sizeof(struct reader_registry) * alloc_readers); | |
289 | alloc_readers <<= 1; | |
290 | free(oldarray); | |
291 | } | |
292 | registry[num_readers].tid = id; | |
293 | /* reference to the TLS of _this_ reader thread. */ | |
3395d46c | 294 | registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; |
9f1621ca MD |
295 | num_readers++; |
296 | } | |
297 | ||
298 | /* | |
299 | * Never shrink (implementation limitation). | |
300 | * This is O(nb threads). Eventually use a hash table. | |
301 | */ | |
302 | static void rcu_remove_reader(pthread_t id) | |
303 | { | |
304 | struct reader_registry *index; | |
305 | ||
306 | assert(registry != NULL); | |
307 | for (index = registry; index < registry + num_readers; index++) { | |
308 | if (pthread_equal(index->tid, id)) { | |
309 | memcpy(index, ®istry[num_readers - 1], | |
310 | sizeof(struct reader_registry)); | |
311 | registry[num_readers - 1].tid = 0; | |
3395d46c | 312 | registry[num_readers - 1].rcu_reader_qs_gp = NULL; |
9f1621ca MD |
313 | num_readers--; |
314 | return; | |
315 | } | |
316 | } | |
317 | /* Hrm not found, forgot to register ? */ | |
318 | assert(0); | |
319 | } | |
320 | ||
321 | void rcu_register_thread(void) | |
322 | { | |
323 | internal_urcu_lock(); | |
9f1621ca MD |
324 | rcu_add_reader(pthread_self()); |
325 | internal_urcu_unlock(); | |
5f373c84 | 326 | _rcu_thread_online(); |
9f1621ca MD |
327 | } |
328 | ||
329 | void rcu_unregister_thread(void) | |
330 | { | |
76f3022f MD |
331 | /* |
332 | * We have to make the thread offline otherwise we end up dealocking | |
333 | * with a waiting writer. | |
334 | */ | |
335 | _rcu_thread_offline(); | |
9f1621ca MD |
336 | internal_urcu_lock(); |
337 | rcu_remove_reader(pthread_self()); | |
338 | internal_urcu_unlock(); | |
339 | } |