urcu-qsbr: use linked list instead of array for registry
[urcu.git] / urcu-qsbr.c
CommitLineData
9f1621ca 1/*
7ac06cef 2 * urcu-qsbr.c
9f1621ca 3 *
7ac06cef 4 * Userspace RCU QSBR library
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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
81d1f1f5 40static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
9f1621ca 41
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42int gp_futex;
43
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44/*
45 * Global grace period counter.
46 */
ac258107 47unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
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48
49/*
50 * Written to only by each individual reader. Read by both the reader and the
51 * writers.
52 */
4f8e3380 53struct urcu_reader __thread urcu_reader;
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54
55#ifdef DEBUG_YIELD
56unsigned int yield_active;
57unsigned int __thread rand_yield;
58#endif
59
4f8e3380 60static LIST_HEAD(registry);
9f1621ca 61
90c1618a 62static void internal_urcu_lock(void)
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63{
64 int ret;
65
66#ifndef DISTRUST_SIGNALS_EXTREME
67 ret = pthread_mutex_lock(&urcu_mutex);
68 if (ret) {
69 perror("Error in pthread mutex lock");
70 exit(-1);
71 }
72#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
73 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
74 if (ret != EBUSY && ret != EINTR) {
75 printf("ret = %d, errno = %d\n", ret, errno);
76 perror("Error in pthread mutex lock");
77 exit(-1);
78 }
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79 poll(NULL,0,10);
80 }
81#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
82}
83
90c1618a 84static void internal_urcu_unlock(void)
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85{
86 int ret;
87
88 ret = pthread_mutex_unlock(&urcu_mutex);
89 if (ret) {
90 perror("Error in pthread mutex unlock");
91 exit(-1);
92 }
93}
94
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95/*
96 * synchronize_rcu() waiting. Single thread.
97 */
4f8e3380 98static void wait_gp(struct urcu_reader *index)
bc6c15bb 99{
ec4e58a3 100 uatomic_dec(&gp_futex);
bc6c15bb 101 smp_mb(); /* Write futex before read reader_gp */
4f8e3380 102 if (!rcu_gp_ongoing(&index->ctr)) {
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103 /* Read reader_gp before write futex */
104 smp_mb();
105 /* Callbacks are queued, don't wait. */
ec4e58a3 106 uatomic_set(&gp_futex, 0);
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107 } else {
108 /* Read reader_gp before read futex */
109 smp_rmb();
ec4e58a3 110 if (uatomic_read(&gp_futex) == -1)
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111 futex(&gp_futex, FUTEX_WAIT, -1,
112 NULL, NULL, 0);
113 }
114}
115
90c1618a 116static void wait_for_quiescent_state(void)
9f1621ca 117{
4f8e3380 118 struct urcu_reader *index;
9f1621ca 119
4f8e3380 120 if (list_empty(&registry))
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121 return;
122 /*
3395d46c 123 * Wait for each thread rcu_reader_qs_gp count to become 0.
9f1621ca 124 */
4f8e3380 125 list_for_each_entry(index, &registry, head) {
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126 int wait_loops = 0;
127
4f8e3380 128 while (rcu_gp_ongoing(&index->ctr)) {
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129 if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
130 wait_gp(index);
131 } else {
9f1621ca 132#ifndef HAS_INCOHERENT_CACHES
bc6c15bb 133 cpu_relax();
9f1621ca 134#else /* #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb 135 smp_mb();
9f1621ca 136#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
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137 }
138 }
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139 }
140}
141
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142/*
143 * Using a two-subphases algorithm for architectures with smaller than 64-bit
144 * long-size to ensure we do not encounter an overflow bug.
145 */
146
147#if (BITS_PER_LONG < 64)
148/*
149 * called with urcu_mutex held.
150 */
151static void switch_next_urcu_qparity(void)
152{
153 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
154}
155
156void synchronize_rcu(void)
157{
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158 unsigned long was_online;
159
4f8e3380 160 was_online = urcu_reader.ctr;
bc49c323 161
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162 /* All threads should read qparity before accessing data structure
163 * where new ptr points to.
164 */
165 /* Write new ptr before changing the qparity */
166 smp_mb();
167
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168 /*
169 * Mark the writer thread offline to make sure we don't wait for
170 * our own quiescent state. This allows using synchronize_rcu() in
171 * threads registered as readers.
172 */
173 if (was_online)
4f8e3380 174 STORE_SHARED(urcu_reader.ctr, 0);
bc49c323 175
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176 internal_urcu_lock();
177
178 switch_next_urcu_qparity(); /* 0 -> 1 */
179
180 /*
181 * Must commit qparity update to memory before waiting for parity
182 * 0 quiescent state. Failure to do so could result in the writer
183 * waiting forever while new readers are always accessing data (no
184 * progress).
185 * Ensured by STORE_SHARED and LOAD_SHARED.
186 */
187
188 /*
189 * Wait for previous parity to be empty of readers.
190 */
191 wait_for_quiescent_state(); /* Wait readers in parity 0 */
192
193 /*
194 * Must finish waiting for quiescent state for parity 0 before
195 * committing qparity update to memory. Failure to do so could result in
196 * the writer waiting forever while new readers are always accessing
197 * data (no progress).
198 * Ensured by STORE_SHARED and LOAD_SHARED.
199 */
200
201 switch_next_urcu_qparity(); /* 1 -> 0 */
202
203 /*
204 * Must commit qparity update to memory before waiting for parity
205 * 1 quiescent state. Failure to do so could result in the writer
206 * waiting forever while new readers are always accessing data (no
207 * progress).
208 * Ensured by STORE_SHARED and LOAD_SHARED.
209 */
210
211 /*
212 * Wait for previous parity to be empty of readers.
213 */
214 wait_for_quiescent_state(); /* Wait readers in parity 1 */
215
216 internal_urcu_unlock();
217
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218 /*
219 * Finish waiting for reader threads before letting the old ptr being
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220 * freed.
221 */
bc49c323 222 if (was_online)
4f8e3380 223 _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
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224 smp_mb();
225}
226#else /* !(BITS_PER_LONG < 64) */
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227void synchronize_rcu(void)
228{
f0f7dbdd 229 unsigned long was_online;
ff2f67a0 230
4f8e3380 231 was_online = urcu_reader.ctr;
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232
233 /*
234 * Mark the writer thread offline to make sure we don't wait for
235 * our own quiescent state. This allows using synchronize_rcu() in
236 * threads registered as readers.
237 */
8f50d1ce 238 smp_mb();
ff2f67a0 239 if (was_online)
4f8e3380 240 STORE_SHARED(urcu_reader.ctr, 0);
ff2f67a0 241
4e27f058 242 internal_urcu_lock();
55570466 243 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca 244 wait_for_quiescent_state();
9f1621ca 245 internal_urcu_unlock();
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246
247 if (was_online)
4f8e3380 248 _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
8f50d1ce 249 smp_mb();
9f1621ca 250}
47d2f29e 251#endif /* !(BITS_PER_LONG < 64) */
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252
253/*
254 * library wrappers to be used by non-LGPL compatible source code.
255 */
256
257void rcu_read_lock(void)
258{
259 _rcu_read_lock();
260}
261
262void rcu_read_unlock(void)
263{
264 _rcu_read_unlock();
265}
266
267void *rcu_dereference(void *p)
268{
269 return _rcu_dereference(p);
270}
271
272void *rcu_assign_pointer_sym(void **p, void *v)
273{
274 wmb();
275 return STORE_SHARED(p, v);
276}
277
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278void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
279{
280 wmb();
ec4e58a3 281 return uatomic_cmpxchg(p, old, _new);
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282}
283
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284void *rcu_xchg_pointer_sym(void **p, void *v)
285{
286 wmb();
ec4e58a3 287 return uatomic_xchg(p, v);
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288}
289
290void *rcu_publish_content_sym(void **p, void *v)
291{
292 void *oldptr;
293
294 oldptr = _rcu_xchg_pointer(p, v);
295 synchronize_rcu();
296 return oldptr;
297}
298
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299void rcu_quiescent_state(void)
300{
301 _rcu_quiescent_state();
302}
303
304void rcu_thread_offline(void)
305{
306 _rcu_thread_offline();
307}
308
309void rcu_thread_online(void)
310{
311 _rcu_thread_online();
312}
313
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314void rcu_register_thread(void)
315{
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316 urcu_reader.tid = pthread_self();
317 assert(urcu_reader.ctr == 0);
318
9f1621ca 319 internal_urcu_lock();
4f8e3380 320 list_add(&urcu_reader.head, &registry);
9f1621ca 321 internal_urcu_unlock();
5f373c84 322 _rcu_thread_online();
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323}
324
325void rcu_unregister_thread(void)
326{
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327 /*
328 * We have to make the thread offline otherwise we end up dealocking
329 * with a waiting writer.
330 */
331 _rcu_thread_offline();
9f1621ca 332 internal_urcu_lock();
4f8e3380 333 list_del(&urcu_reader.head);
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334 internal_urcu_unlock();
335}
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