qsbr urcu: simplifications and fixes.
[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
7ac06cef 35#include "urcu-qsbr-static.h"
9f1621ca 36/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
7ac06cef 37#include "urcu-qsbr.h"
9f1621ca 38
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39pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
40
41/*
42 * Global grace period counter.
43 */
44long 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 50long __thread rcu_reader_qs_gp;
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51
52/* Thread IDs of registered readers */
53#define INIT_NUM_THREADS 4
54
55struct reader_registry {
56 pthread_t tid;
3395d46c 57 long *rcu_reader_qs_gp;
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58};
59
60#ifdef DEBUG_YIELD
61unsigned int yield_active;
62unsigned int __thread rand_yield;
63#endif
64
65static struct reader_registry *registry;
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66static int num_readers, alloc_readers;
67
90c1618a 68static void internal_urcu_lock(void)
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69{
70 int ret;
71
72#ifndef DISTRUST_SIGNALS_EXTREME
73 ret = pthread_mutex_lock(&urcu_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(&urcu_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 }
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85 poll(NULL,0,10);
86 }
87#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
88}
89
90c1618a 90static void internal_urcu_unlock(void)
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91{
92 int ret;
93
94 ret = pthread_mutex_unlock(&urcu_mutex);
95 if (ret) {
96 perror("Error in pthread mutex unlock");
97 exit(-1);
98 }
99}
100
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101#ifdef HAS_INCOHERENT_CACHES
102static void force_mb_single_thread(struct reader_registry *index)
103{
104 smp_mb();
105}
106#endif /* #ifdef HAS_INCOHERENT_CACHES */
107
108static void force_mb_all_threads(void)
109{
110 smp_mb();
111}
9f1621ca 112
90c1618a 113static void wait_for_quiescent_state(void)
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114{
115 struct reader_registry *index;
116
117 if (!registry)
118 return;
119 /*
3395d46c 120 * Wait for each thread rcu_reader_qs_gp count to become 0.
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121 */
122 for (index = registry; index < registry + num_readers; index++) {
123#ifndef HAS_INCOHERENT_CACHES
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124 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
125 (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
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126 cpu_relax();
127#else /* #ifndef HAS_INCOHERENT_CACHES */
128 int wait_loops = 0;
129 /*
130 * BUSY-LOOP. Force the reader thread to commit its
3395d46c 131 * rcu_reader_qs_gp update to memory if we wait for too long.
9f1621ca 132 */
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133 while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
134 (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
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135 if (wait_loops++ == KICK_READER_LOOPS) {
136 force_mb_single_thread(index);
137 wait_loops = 0;
138 } else {
139 cpu_relax();
140 }
141 }
142#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
143 }
144}
145
146void synchronize_rcu(void)
147{
148 internal_urcu_lock();
149 force_mb_all_threads();
150 urcu_gp_ctr += 2;
151 wait_for_quiescent_state();
152 force_mb_all_threads();
153 internal_urcu_unlock();
154}
155
156/*
157 * library wrappers to be used by non-LGPL compatible source code.
158 */
159
160void rcu_read_lock(void)
161{
162 _rcu_read_lock();
163}
164
165void rcu_read_unlock(void)
166{
167 _rcu_read_unlock();
168}
169
170void *rcu_dereference(void *p)
171{
172 return _rcu_dereference(p);
173}
174
175void *rcu_assign_pointer_sym(void **p, void *v)
176{
177 wmb();
178 return STORE_SHARED(p, v);
179}
180
181void *rcu_xchg_pointer_sym(void **p, void *v)
182{
183 wmb();
184 return xchg(p, v);
185}
186
187void *rcu_publish_content_sym(void **p, void *v)
188{
189 void *oldptr;
190
191 oldptr = _rcu_xchg_pointer(p, v);
192 synchronize_rcu();
193 return oldptr;
194}
195
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196void rcu_quiescent_state(void)
197{
198 _rcu_quiescent_state();
199}
200
201void rcu_thread_offline(void)
202{
203 _rcu_thread_offline();
204}
205
206void rcu_thread_online(void)
207{
208 _rcu_thread_online();
209}
210
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211static void rcu_add_reader(pthread_t id)
212{
213 struct reader_registry *oldarray;
214
215 if (!registry) {
216 alloc_readers = INIT_NUM_THREADS;
217 num_readers = 0;
218 registry =
219 malloc(sizeof(struct reader_registry) * alloc_readers);
220 }
221 if (alloc_readers < num_readers + 1) {
222 oldarray = registry;
223 registry = malloc(sizeof(struct reader_registry)
224 * (alloc_readers << 1));
225 memcpy(registry, oldarray,
226 sizeof(struct reader_registry) * alloc_readers);
227 alloc_readers <<= 1;
228 free(oldarray);
229 }
230 registry[num_readers].tid = id;
231 /* reference to the TLS of _this_ reader thread. */
3395d46c 232 registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
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233 num_readers++;
234}
235
236/*
237 * Never shrink (implementation limitation).
238 * This is O(nb threads). Eventually use a hash table.
239 */
240static void rcu_remove_reader(pthread_t id)
241{
242 struct reader_registry *index;
243
244 assert(registry != NULL);
245 for (index = registry; index < registry + num_readers; index++) {
246 if (pthread_equal(index->tid, id)) {
247 memcpy(index, &registry[num_readers - 1],
248 sizeof(struct reader_registry));
249 registry[num_readers - 1].tid = 0;
3395d46c 250 registry[num_readers - 1].rcu_reader_qs_gp = NULL;
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251 num_readers--;
252 return;
253 }
254 }
255 /* Hrm not found, forgot to register ? */
256 assert(0);
257}
258
259void rcu_register_thread(void)
260{
261 internal_urcu_lock();
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262 rcu_add_reader(pthread_self());
263 internal_urcu_unlock();
5f373c84 264 _rcu_thread_online();
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265}
266
267void rcu_unregister_thread(void)
268{
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269 /*
270 * We have to make the thread offline otherwise we end up dealocking
271 * with a waiting writer.
272 */
273 _rcu_thread_offline();
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274 internal_urcu_lock();
275 rcu_remove_reader(pthread_self());
276 internal_urcu_unlock();
277}
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