add rcu_cmpxchg_pointer
[urcu.git] / urcu-qsbr.c
1 /*
2 * urcu-qsbr.c
3 *
4 * Userspace RCU QSBR 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
35 #define BUILD_QSBR_LIB
36 #include "urcu-qsbr-static.h"
37 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
38 #include "urcu-qsbr.h"
39
40 static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
41
42 /*
43 * Global grace period counter.
44 */
45 unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
46
47 /*
48 * Written to only by each individual reader. Read by both the reader and the
49 * writers.
50 */
51 unsigned long __thread rcu_reader_qs_gp;
52
53 /* Thread IDs of registered readers */
54 #define INIT_NUM_THREADS 4
55
56 struct reader_registry {
57 pthread_t tid;
58 unsigned long *rcu_reader_qs_gp;
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 int num_readers, alloc_readers;
68
69 static void internal_urcu_lock(void)
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 }
86 poll(NULL,0,10);
87 }
88 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
89 }
90
91 static void internal_urcu_unlock(void)
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
102 static void wait_for_quiescent_state(void)
103 {
104 struct reader_registry *index;
105
106 if (!registry)
107 return;
108 /*
109 * Wait for each thread rcu_reader_qs_gp count to become 0.
110 */
111 for (index = registry; index < registry + num_readers; index++) {
112 #ifndef HAS_INCOHERENT_CACHES
113 while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
114 cpu_relax();
115 #else /* #ifndef HAS_INCOHERENT_CACHES */
116 while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
117 smp_mb();
118 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
119 }
120 }
121
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 unsigned long was_online;
139
140 was_online = rcu_reader_qs_gp;
141
142 /* All threads should read qparity before accessing data structure
143 * where new ptr points to.
144 */
145 /* Write new ptr before changing the qparity */
146 smp_mb();
147
148 /*
149 * Mark the writer thread offline to make sure we don't wait for
150 * our own quiescent state. This allows using synchronize_rcu() in
151 * threads registered as readers.
152 */
153 if (was_online)
154 STORE_SHARED(rcu_reader_qs_gp, 0);
155
156 internal_urcu_lock();
157
158 switch_next_urcu_qparity(); /* 0 -> 1 */
159
160 /*
161 * Must commit qparity update to memory before waiting for parity
162 * 0 quiescent state. Failure to do so could result in the writer
163 * waiting forever while new readers are always accessing data (no
164 * progress).
165 * Ensured by STORE_SHARED and LOAD_SHARED.
166 */
167
168 /*
169 * Wait for previous parity to be empty of readers.
170 */
171 wait_for_quiescent_state(); /* Wait readers in parity 0 */
172
173 /*
174 * Must finish waiting for quiescent state for parity 0 before
175 * committing qparity update to memory. Failure to do so could result in
176 * the writer waiting forever while new readers are always accessing
177 * data (no progress).
178 * Ensured by STORE_SHARED and LOAD_SHARED.
179 */
180
181 switch_next_urcu_qparity(); /* 1 -> 0 */
182
183 /*
184 * Must commit qparity update to memory before waiting for parity
185 * 1 quiescent state. Failure to do so could result in the writer
186 * waiting forever while new readers are always accessing data (no
187 * progress).
188 * Ensured by STORE_SHARED and LOAD_SHARED.
189 */
190
191 /*
192 * Wait for previous parity to be empty of readers.
193 */
194 wait_for_quiescent_state(); /* Wait readers in parity 1 */
195
196 internal_urcu_unlock();
197
198 /*
199 * Finish waiting for reader threads before letting the old ptr being
200 * freed.
201 */
202 if (was_online)
203 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
204 smp_mb();
205 }
206 #else /* !(BITS_PER_LONG < 64) */
207 void synchronize_rcu(void)
208 {
209 unsigned long was_online;
210
211 was_online = rcu_reader_qs_gp;
212
213 /*
214 * Mark the writer thread offline to make sure we don't wait for
215 * our own quiescent state. This allows using synchronize_rcu() in
216 * threads registered as readers.
217 */
218 smp_mb();
219 if (was_online)
220 STORE_SHARED(rcu_reader_qs_gp, 0);
221
222 internal_urcu_lock();
223 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
224 wait_for_quiescent_state();
225 internal_urcu_unlock();
226
227 if (was_online)
228 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
229 smp_mb();
230 }
231 #endif /* !(BITS_PER_LONG < 64) */
232
233 /*
234 * library wrappers to be used by non-LGPL compatible source code.
235 */
236
237 void rcu_read_lock(void)
238 {
239 _rcu_read_lock();
240 }
241
242 void rcu_read_unlock(void)
243 {
244 _rcu_read_unlock();
245 }
246
247 void *rcu_dereference(void *p)
248 {
249 return _rcu_dereference(p);
250 }
251
252 void *rcu_assign_pointer_sym(void **p, void *v)
253 {
254 wmb();
255 return STORE_SHARED(p, v);
256 }
257
258 void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
259 {
260 wmb();
261 return cmpxchg(p, old, _new);
262 }
263
264 void *rcu_xchg_pointer_sym(void **p, void *v)
265 {
266 wmb();
267 return xchg(p, v);
268 }
269
270 void *rcu_publish_content_sym(void **p, void *v)
271 {
272 void *oldptr;
273
274 oldptr = _rcu_xchg_pointer(p, v);
275 synchronize_rcu();
276 return oldptr;
277 }
278
279 void rcu_quiescent_state(void)
280 {
281 _rcu_quiescent_state();
282 }
283
284 void rcu_thread_offline(void)
285 {
286 _rcu_thread_offline();
287 }
288
289 void rcu_thread_online(void)
290 {
291 _rcu_thread_online();
292 }
293
294 static void rcu_add_reader(pthread_t id)
295 {
296 struct reader_registry *oldarray;
297
298 if (!registry) {
299 alloc_readers = INIT_NUM_THREADS;
300 num_readers = 0;
301 registry =
302 malloc(sizeof(struct reader_registry) * alloc_readers);
303 }
304 if (alloc_readers < num_readers + 1) {
305 oldarray = registry;
306 registry = malloc(sizeof(struct reader_registry)
307 * (alloc_readers << 1));
308 memcpy(registry, oldarray,
309 sizeof(struct reader_registry) * alloc_readers);
310 alloc_readers <<= 1;
311 free(oldarray);
312 }
313 registry[num_readers].tid = id;
314 /* reference to the TLS of _this_ reader thread. */
315 registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
316 num_readers++;
317 }
318
319 /*
320 * Never shrink (implementation limitation).
321 * This is O(nb threads). Eventually use a hash table.
322 */
323 static void rcu_remove_reader(pthread_t id)
324 {
325 struct reader_registry *index;
326
327 assert(registry != NULL);
328 for (index = registry; index < registry + num_readers; index++) {
329 if (pthread_equal(index->tid, id)) {
330 memcpy(index, &registry[num_readers - 1],
331 sizeof(struct reader_registry));
332 registry[num_readers - 1].tid = 0;
333 registry[num_readers - 1].rcu_reader_qs_gp = NULL;
334 num_readers--;
335 return;
336 }
337 }
338 /* Hrm not found, forgot to register ? */
339 assert(0);
340 }
341
342 void rcu_register_thread(void)
343 {
344 internal_urcu_lock();
345 rcu_add_reader(pthread_self());
346 internal_urcu_unlock();
347 _rcu_thread_online();
348 }
349
350 void rcu_unregister_thread(void)
351 {
352 /*
353 * We have to make the thread offline otherwise we end up dealocking
354 * with a waiting writer.
355 */
356 _rcu_thread_offline();
357 internal_urcu_lock();
358 rcu_remove_reader(pthread_self());
359 internal_urcu_unlock();
360 }
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