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[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@efficios.com>
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 #define _GNU_SOURCE
27 #include <stdio.h>
28 #include <pthread.h>
29 #include <signal.h>
30 #include <assert.h>
31 #include <stdlib.h>
32 #include <stdint.h>
33 #include <string.h>
34 #include <errno.h>
35 #include <poll.h>
36
37 #include "urcu/map/urcu-qsbr.h"
38
39 #define BUILD_QSBR_LIB
40 #include "urcu/static/urcu-qsbr.h"
41 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
42 #include "urcu-qsbr.h"
43
44 void __attribute__((destructor)) rcu_exit(void);
45
46 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
47
48 int32_t gp_futex;
49
50 /*
51 * Global grace period counter.
52 */
53 unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
54
55 /*
56 * Written to only by each individual reader. Read by both the reader and the
57 * writers.
58 */
59 struct rcu_reader __thread rcu_reader;
60
61 #ifdef DEBUG_YIELD
62 unsigned int yield_active;
63 unsigned int __thread rand_yield;
64 #endif
65
66 static CDS_LIST_HEAD(registry);
67
68 static void mutex_lock(pthread_mutex_t *mutex)
69 {
70 int ret;
71
72 #ifndef DISTRUST_SIGNALS_EXTREME
73 ret = pthread_mutex_lock(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(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 }
85 poll(NULL,0,10);
86 }
87 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
88 }
89
90 static void mutex_unlock(pthread_mutex_t *mutex)
91 {
92 int ret;
93
94 ret = pthread_mutex_unlock(mutex);
95 if (ret) {
96 perror("Error in pthread mutex unlock");
97 exit(-1);
98 }
99 }
100
101 /*
102 * synchronize_rcu() waiting. Single thread.
103 */
104 static void wait_gp(void)
105 {
106 /* Read reader_gp before read futex */
107 cmm_smp_rmb();
108 if (uatomic_read(&gp_futex) == -1)
109 futex_noasync(&gp_futex, FUTEX_WAIT, -1,
110 NULL, NULL, 0);
111 }
112
113 static void update_counter_and_wait(void)
114 {
115 CDS_LIST_HEAD(qsreaders);
116 int wait_loops = 0;
117 struct rcu_reader *index, *tmp;
118
119 #if (CAA_BITS_PER_LONG < 64)
120 /* Switch parity: 0 -> 1, 1 -> 0 */
121 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
122 #else /* !(CAA_BITS_PER_LONG < 64) */
123 /* Increment current G.P. */
124 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
125 #endif /* !(CAA_BITS_PER_LONG < 64) */
126
127 /*
128 * Must commit rcu_gp_ctr update to memory before waiting for
129 * quiescent state. Failure to do so could result in the writer
130 * waiting forever while new readers are always accessing data
131 * (no progress). Enforce compiler-order of store to rcu_gp_ctr
132 * before load rcu_reader ctr.
133 */
134 cmm_barrier();
135
136 /*
137 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
138 * model easier to understand. It does not have a big performance impact
139 * anyway, given this is the write-side.
140 */
141 cmm_smp_mb();
142
143 /*
144 * Wait for each thread rcu_reader_qs_gp count to become 0.
145 */
146 for (;;) {
147 wait_loops++;
148 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
149 uatomic_dec(&gp_futex);
150 /* Write futex before read reader_gp */
151 cmm_smp_mb();
152 }
153
154 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
155 if (!rcu_gp_ongoing(&index->ctr))
156 cds_list_move(&index->node, &qsreaders);
157 }
158
159 if (cds_list_empty(&registry)) {
160 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
161 /* Read reader_gp before write futex */
162 cmm_smp_mb();
163 uatomic_set(&gp_futex, 0);
164 }
165 break;
166 } else {
167 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
168 wait_gp();
169 } else {
170 #ifndef HAS_INCOHERENT_CACHES
171 caa_cpu_relax();
172 #else /* #ifndef HAS_INCOHERENT_CACHES */
173 cmm_smp_mb();
174 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
175 }
176 }
177 }
178 /* put back the reader list in the registry */
179 cds_list_splice(&qsreaders, &registry);
180 }
181
182 /*
183 * Using a two-subphases algorithm for architectures with smaller than 64-bit
184 * long-size to ensure we do not encounter an overflow bug.
185 */
186
187 #if (CAA_BITS_PER_LONG < 64)
188 void synchronize_rcu(void)
189 {
190 unsigned long was_online;
191
192 was_online = rcu_reader.ctr;
193
194 /* All threads should read qparity before accessing data structure
195 * where new ptr points to.
196 */
197 /* Write new ptr before changing the qparity */
198 cmm_smp_mb();
199
200 /*
201 * Mark the writer thread offline to make sure we don't wait for
202 * our own quiescent state. This allows using synchronize_rcu()
203 * in threads registered as readers.
204 */
205 if (was_online)
206 CMM_STORE_SHARED(rcu_reader.ctr, 0);
207
208 mutex_lock(&rcu_gp_lock);
209
210 if (cds_list_empty(&registry))
211 goto out;
212
213 /*
214 * Wait for previous parity to be empty of readers.
215 */
216 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
217
218 /*
219 * Must finish waiting for quiescent state for parity 0 before
220 * committing next rcu_gp_ctr update to memory. Failure to
221 * do so could result in the writer waiting forever while new
222 * readers are always accessing data (no progress). Enforce
223 * compiler-order of load rcu_reader ctr before store to
224 * rcu_gp_ctr.
225 */
226 cmm_barrier();
227
228 /*
229 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
230 * model easier to understand. It does not have a big performance impact
231 * anyway, given this is the write-side.
232 */
233 cmm_smp_mb();
234
235 /*
236 * Wait for previous parity to be empty of readers.
237 */
238 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
239 out:
240 mutex_unlock(&rcu_gp_lock);
241
242 /*
243 * Finish waiting for reader threads before letting the old ptr being
244 * freed.
245 */
246 if (was_online)
247 _CMM_STORE_SHARED(rcu_reader.ctr,
248 CMM_LOAD_SHARED(rcu_gp_ctr));
249 cmm_smp_mb();
250 }
251 #else /* !(CAA_BITS_PER_LONG < 64) */
252 void synchronize_rcu(void)
253 {
254 unsigned long was_online;
255
256 was_online = rcu_reader.ctr;
257
258 /*
259 * Mark the writer thread offline to make sure we don't wait for
260 * our own quiescent state. This allows using synchronize_rcu()
261 * in threads registered as readers.
262 */
263 cmm_smp_mb();
264 if (was_online)
265 CMM_STORE_SHARED(rcu_reader.ctr, 0);
266
267 mutex_lock(&rcu_gp_lock);
268 if (cds_list_empty(&registry))
269 goto out;
270 update_counter_and_wait();
271 out:
272 mutex_unlock(&rcu_gp_lock);
273
274 if (was_online)
275 _CMM_STORE_SHARED(rcu_reader.ctr,
276 CMM_LOAD_SHARED(rcu_gp_ctr));
277 cmm_smp_mb();
278 }
279 #endif /* !(CAA_BITS_PER_LONG < 64) */
280
281 /*
282 * library wrappers to be used by non-LGPL compatible source code.
283 */
284
285 void rcu_read_lock(void)
286 {
287 _rcu_read_lock();
288 }
289
290 void rcu_read_unlock(void)
291 {
292 _rcu_read_unlock();
293 }
294
295 void rcu_quiescent_state(void)
296 {
297 _rcu_quiescent_state();
298 }
299
300 void rcu_thread_offline(void)
301 {
302 _rcu_thread_offline();
303 }
304
305 void rcu_thread_online(void)
306 {
307 _rcu_thread_online();
308 }
309
310 void rcu_register_thread(void)
311 {
312 rcu_reader.tid = pthread_self();
313 assert(rcu_reader.ctr == 0);
314
315 mutex_lock(&rcu_gp_lock);
316 cds_list_add(&rcu_reader.node, &registry);
317 mutex_unlock(&rcu_gp_lock);
318 _rcu_thread_online();
319 }
320
321 void rcu_unregister_thread(void)
322 {
323 /*
324 * We have to make the thread offline otherwise we end up dealocking
325 * with a waiting writer.
326 */
327 _rcu_thread_offline();
328 mutex_lock(&rcu_gp_lock);
329 cds_list_del(&rcu_reader.node);
330 mutex_unlock(&rcu_gp_lock);
331 }
332
333 void rcu_exit(void)
334 {
335 assert(cds_list_empty(&registry));
336 }
337
338 #include "urcu-call-rcu-impl.h"
339 #include "urcu-defer-impl.h"
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