urcu-bp: New "bulletproof" RCU library flavor
[urcu.git] / urcu-bp.c
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1/*
2 * urcu-bp.c
3 *
4 * Userspace RCU library, "bulletproof" version.
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#include <unistd.h>
35#include <sys/mman.h>
36
37#include "urcu-bp-static.h"
38/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
39#include "urcu-bp.h"
40
41/* Sleep delay in us */
42#define RCU_SLEEP_DELAY 1000
43#define ARENA_INIT_ALLOC 16
44
45void __attribute__((destructor)) urcu_bp_exit(void);
46
47static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
48
49#ifdef DEBUG_YIELD
50unsigned int yield_active;
51unsigned int __thread rand_yield;
52#endif
53
54/*
55 * Global grace period counter.
56 * Contains the current RCU_GP_CTR_BIT.
57 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
58 * Written to only by writer with mutex taken. Read by both writer and readers.
59 */
60long urcu_gp_ctr = RCU_GP_COUNT;
61
62/*
63 * Pointer to registry elements. Written to only by each individual reader. Read
64 * by both the reader and the writers.
65 */
66struct urcu_reader __thread *urcu_reader;
67
68static LIST_HEAD(registry);
69
70struct registry_arena {
71 void *p;
72 size_t len;
73 size_t used;
74};
75
76static struct registry_arena registry_arena;
77
78static void rcu_gc_registry(void);
79
80static void internal_urcu_lock(void)
81{
82 int ret;
83
84#ifndef DISTRUST_SIGNALS_EXTREME
85 ret = pthread_mutex_lock(&urcu_mutex);
86 if (ret) {
87 perror("Error in pthread mutex lock");
88 exit(-1);
89 }
90#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
91 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
92 if (ret != EBUSY && ret != EINTR) {
93 printf("ret = %d, errno = %d\n", ret, errno);
94 perror("Error in pthread mutex lock");
95 exit(-1);
96 }
97 if (urcu_reader.need_mb) {
98 smp_mb();
99 urcu_reader.need_mb = 0;
100 smp_mb();
101 }
102 poll(NULL,0,10);
103 }
104#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
105}
106
107static void internal_urcu_unlock(void)
108{
109 int ret;
110
111 ret = pthread_mutex_unlock(&urcu_mutex);
112 if (ret) {
113 perror("Error in pthread mutex unlock");
114 exit(-1);
115 }
116}
117
118/*
119 * called with urcu_mutex held.
120 */
121static void switch_next_urcu_qparity(void)
122{
123 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
124}
125
126void wait_for_quiescent_state(void)
127{
128 LIST_HEAD(qsreaders);
129 int wait_loops = 0;
130 struct urcu_reader *index, *tmp;
131
132 if (list_empty(&registry))
133 return;
134 /*
135 * Wait for each thread urcu_reader.ctr count to become 0.
136 */
137 for (;;) {
138 wait_loops++;
139 list_for_each_entry_safe(index, tmp, &registry, head) {
140 if (!rcu_old_gp_ongoing(&index->ctr))
141 list_move(&index->head, &qsreaders);
142 }
143
144 if (list_empty(&registry)) {
145 break;
146 } else {
147 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
148 usleep(RCU_SLEEP_DELAY);
149 else
150 cpu_relax();
151 }
152 }
153 /* put back the reader list in the registry */
154 list_splice(&qsreaders, &registry);
155}
156
157void synchronize_rcu(void)
158{
159 sigset_t newmask, oldmask;
160 int ret;
161
162 ret = sigemptyset(&newmask);
163 assert(!ret);
164 ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
165 assert(!ret);
166
167 internal_urcu_lock();
168
169 /* Remove old registry elements */
170 rcu_gc_registry();
171
172 /* All threads should read qparity before accessing data structure
173 * where new ptr points to. Must be done within internal_urcu_lock
174 * because it iterates on reader threads.*/
175 /* Write new ptr before changing the qparity */
176 smp_mb();
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 * Adding a smp_mb() which is _not_ formally required, but makes the
190 * model easier to understand. It does not have a big performance impact
191 * anyway, given this is the write-side.
192 */
193 smp_mb();
194
195 /*
196 * Wait for previous parity to be empty of readers.
197 */
198 wait_for_quiescent_state(); /* Wait readers in parity 0 */
199
200 /*
201 * Must finish waiting for quiescent state for parity 0 before
202 * committing qparity update to memory. Failure to do so could result in
203 * the writer waiting forever while new readers are always accessing
204 * data (no progress).
205 * Ensured by STORE_SHARED and LOAD_SHARED.
206 */
207
208 /*
209 * Adding a smp_mb() which is _not_ formally required, but makes the
210 * model easier to understand. It does not have a big performance impact
211 * anyway, given this is the write-side.
212 */
213 smp_mb();
214
215 switch_next_urcu_qparity(); /* 1 -> 0 */
216
217 /*
218 * Must commit qparity update to memory before waiting for parity
219 * 1 quiescent state. Failure to do so could result in the writer
220 * waiting forever while new readers are always accessing data (no
221 * progress).
222 * Ensured by STORE_SHARED and LOAD_SHARED.
223 */
224
225 /*
226 * Adding a smp_mb() which is _not_ formally required, but makes the
227 * model easier to understand. It does not have a big performance impact
228 * anyway, given this is the write-side.
229 */
230 smp_mb();
231
232 /*
233 * Wait for previous parity to be empty of readers.
234 */
235 wait_for_quiescent_state(); /* Wait readers in parity 1 */
236
237 /* Finish waiting for reader threads before letting the old ptr being
238 * freed. Must be done within internal_urcu_lock because it iterates on
239 * reader threads. */
240 smp_mb();
241
242 internal_urcu_unlock();
243 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
244 assert(!ret);
245}
246
247/*
248 * library wrappers to be used by non-LGPL compatible source code.
249 */
250
251void rcu_read_lock(void)
252{
253 _rcu_read_lock();
254}
255
256void rcu_read_unlock(void)
257{
258 _rcu_read_unlock();
259}
260
261/*
262 * only grow for now.
263 */
264static void resize_arena(struct registry_arena *arena, size_t len)
265{
266 void *new_arena;
267
268 new_arena = mmap(arena->p, len,
269 PROT_READ | PROT_WRITE,
270 MAP_ANONYMOUS | MAP_PRIVATE,
271 -1, 0);
272 /*
273 * re-used the same region ?
274 */
275 if (new_arena == arena->p)
276 return;
277
278 memcpy(new_arena, arena->p, arena->len);
279 bzero(new_arena + arena->len, len - arena->len);
280 arena->p = new_arena;
281}
282
283/* Called with signals off and mutex locked */
284static void add_thread(void)
285{
286 struct urcu_reader *urcu_reader_reg;
287
288 if (registry_arena.len
289 < registry_arena.used + sizeof(struct urcu_reader))
290 resize_arena(&registry_arena,
291 max(registry_arena.len << 1, ARENA_INIT_ALLOC));
292 /*
293 * Find a free spot.
294 */
295 for (urcu_reader_reg = registry_arena.p;
296 (void *)urcu_reader_reg < registry_arena.p + registry_arena.len;
297 urcu_reader_reg++) {
298 if (!urcu_reader_reg->alloc)
299 break;
300 }
301 urcu_reader_reg->alloc = 1;
302 registry_arena.used += sizeof(struct urcu_reader);
303
304 /* Add to registry */
305 urcu_reader_reg->tid = pthread_self();
306 assert(urcu_reader_reg->ctr == 0);
307 list_add(&urcu_reader_reg->head, &registry);
308 urcu_reader = urcu_reader_reg;
309}
310
311/* Called with signals off and mutex locked */
312static void rcu_gc_registry(void)
313{
314 struct urcu_reader *urcu_reader_reg;
315 pthread_t tid;
316 int ret;
317
318 for (urcu_reader_reg = registry_arena.p;
319 (void *)urcu_reader_reg < registry_arena.p + registry_arena.len;
320 urcu_reader_reg++) {
321 if (!urcu_reader_reg->alloc)
322 continue;
323 tid = urcu_reader_reg->tid;
324 ret = pthread_kill(tid, 0);
325 assert(ret != EINVAL);
326 if (ret == ESRCH) {
327 list_del(&urcu_reader_reg->head);
328 urcu_reader_reg->alloc = 0;
329 registry_arena.used -= sizeof(struct urcu_reader);
330 }
331 }
332}
333
334/* Disable signals, take mutex, add to registry */
335void rcu_bp_register(void)
336{
337 sigset_t newmask, oldmask;
338 int ret;
339
340 ret = sigemptyset(&newmask);
341 assert(!ret);
342 ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
343 assert(!ret);
344
345 /*
346 * Check if a signal concurrently registered our thread since
347 * the check in rcu_read_lock(). */
348 if (urcu_reader)
349 goto end;
350
351 internal_urcu_lock();
352 add_thread();
353 internal_urcu_unlock();
354end:
355 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
356 assert(!ret);
357}
358
359void urcu_bp_exit()
360{
361 munmap(registry_arena.p, registry_arena.len);
362}
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