urcu-bp: use mremap
[urcu.git] / urcu-bp.c
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 #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 <string.h>
33 #include <errno.h>
34 #include <poll.h>
35 #include <unistd.h>
36 #include <sys/mman.h>
37
38 #include "urcu-bp-static.h"
39 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
40 #include "urcu-bp.h"
41
42 /* Sleep delay in us */
43 #define RCU_SLEEP_DELAY 1000
44 #define ARENA_INIT_ALLOC 16
45
46 void __attribute__((destructor)) urcu_bp_exit(void);
47
48 static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
49
50 #ifdef DEBUG_YIELD
51 unsigned int yield_active;
52 unsigned int __thread rand_yield;
53 #endif
54
55 /*
56 * Global grace period counter.
57 * Contains the current RCU_GP_CTR_BIT.
58 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
59 * Written to only by writer with mutex taken. Read by both writer and readers.
60 */
61 long urcu_gp_ctr = RCU_GP_COUNT;
62
63 /*
64 * Pointer to registry elements. Written to only by each individual reader. Read
65 * by both the reader and the writers.
66 */
67 struct urcu_reader __thread *urcu_reader;
68
69 static LIST_HEAD(registry);
70
71 struct registry_arena {
72 void *p;
73 size_t len;
74 size_t used;
75 };
76
77 static struct registry_arena registry_arena;
78
79 static void rcu_gc_registry(void);
80
81 static void internal_urcu_lock(void)
82 {
83 int ret;
84
85 #ifndef DISTRUST_SIGNALS_EXTREME
86 ret = pthread_mutex_lock(&urcu_mutex);
87 if (ret) {
88 perror("Error in pthread mutex lock");
89 exit(-1);
90 }
91 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
92 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
93 if (ret != EBUSY && ret != EINTR) {
94 printf("ret = %d, errno = %d\n", ret, errno);
95 perror("Error in pthread mutex lock");
96 exit(-1);
97 }
98 if (urcu_reader.need_mb) {
99 smp_mb();
100 urcu_reader.need_mb = 0;
101 smp_mb();
102 }
103 poll(NULL,0,10);
104 }
105 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
106 }
107
108 static void internal_urcu_unlock(void)
109 {
110 int ret;
111
112 ret = pthread_mutex_unlock(&urcu_mutex);
113 if (ret) {
114 perror("Error in pthread mutex unlock");
115 exit(-1);
116 }
117 }
118
119 /*
120 * called with urcu_mutex held.
121 */
122 static void switch_next_urcu_qparity(void)
123 {
124 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
125 }
126
127 void wait_for_quiescent_state(void)
128 {
129 LIST_HEAD(qsreaders);
130 int wait_loops = 0;
131 struct urcu_reader *index, *tmp;
132
133 if (list_empty(&registry))
134 return;
135 /*
136 * Wait for each thread urcu_reader.ctr count to become 0.
137 */
138 for (;;) {
139 wait_loops++;
140 list_for_each_entry_safe(index, tmp, &registry, head) {
141 if (!rcu_old_gp_ongoing(&index->ctr))
142 list_move(&index->head, &qsreaders);
143 }
144
145 if (list_empty(&registry)) {
146 break;
147 } else {
148 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
149 usleep(RCU_SLEEP_DELAY);
150 else
151 cpu_relax();
152 }
153 }
154 /* put back the reader list in the registry */
155 list_splice(&qsreaders, &registry);
156 }
157
158 void synchronize_rcu(void)
159 {
160 sigset_t newmask, oldmask;
161 int ret;
162
163 ret = sigemptyset(&newmask);
164 assert(!ret);
165 ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
166 assert(!ret);
167
168 internal_urcu_lock();
169
170 /* Remove old registry elements */
171 rcu_gc_registry();
172
173 /* All threads should read qparity before accessing data structure
174 * where new ptr points to. Must be done within internal_urcu_lock
175 * because it iterates on reader threads.*/
176 /* Write new ptr before changing the qparity */
177 smp_mb();
178
179 switch_next_urcu_qparity(); /* 0 -> 1 */
180
181 /*
182 * Must commit qparity update to memory before waiting for parity
183 * 0 quiescent state. Failure to do so could result in the writer
184 * waiting forever while new readers are always accessing data (no
185 * progress).
186 * Ensured by STORE_SHARED and LOAD_SHARED.
187 */
188
189 /*
190 * Adding a smp_mb() which is _not_ formally required, but makes the
191 * model easier to understand. It does not have a big performance impact
192 * anyway, given this is the write-side.
193 */
194 smp_mb();
195
196 /*
197 * Wait for previous parity to be empty of readers.
198 */
199 wait_for_quiescent_state(); /* Wait readers in parity 0 */
200
201 /*
202 * Must finish waiting for quiescent state for parity 0 before
203 * committing qparity update to memory. Failure to do so could result in
204 * the writer waiting forever while new readers are always accessing
205 * data (no progress).
206 * Ensured by STORE_SHARED and LOAD_SHARED.
207 */
208
209 /*
210 * Adding a smp_mb() which is _not_ formally required, but makes the
211 * model easier to understand. It does not have a big performance impact
212 * anyway, given this is the write-side.
213 */
214 smp_mb();
215
216 switch_next_urcu_qparity(); /* 1 -> 0 */
217
218 /*
219 * Must commit qparity update to memory before waiting for parity
220 * 1 quiescent state. Failure to do so could result in the writer
221 * waiting forever while new readers are always accessing data (no
222 * progress).
223 * Ensured by STORE_SHARED and LOAD_SHARED.
224 */
225
226 /*
227 * Adding a smp_mb() which is _not_ formally required, but makes the
228 * model easier to understand. It does not have a big performance impact
229 * anyway, given this is the write-side.
230 */
231 smp_mb();
232
233 /*
234 * Wait for previous parity to be empty of readers.
235 */
236 wait_for_quiescent_state(); /* Wait readers in parity 1 */
237
238 /* Finish waiting for reader threads before letting the old ptr being
239 * freed. Must be done within internal_urcu_lock because it iterates on
240 * reader threads. */
241 smp_mb();
242
243 internal_urcu_unlock();
244 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
245 assert(!ret);
246 }
247
248 /*
249 * library wrappers to be used by non-LGPL compatible source code.
250 */
251
252 void rcu_read_lock(void)
253 {
254 _rcu_read_lock();
255 }
256
257 void rcu_read_unlock(void)
258 {
259 _rcu_read_unlock();
260 }
261
262 /*
263 * only grow for now.
264 */
265 static void resize_arena(struct registry_arena *arena, size_t len)
266 {
267 void *new_arena;
268
269 if (!arena->p)
270 new_arena = mmap(arena->p, len,
271 PROT_READ | PROT_WRITE,
272 MAP_ANONYMOUS | MAP_PRIVATE,
273 -1, 0);
274 else
275 new_arena = mremap(arena->p, arena->len,
276 len, MREMAP_MAYMOVE);
277 assert(new_arena != MAP_FAILED);
278
279 /*
280 * re-used the same region ?
281 */
282 if (new_arena == arena->p)
283 return;
284
285 memcpy(new_arena, arena->p, arena->len);
286 bzero(new_arena + arena->len, len - arena->len);
287 arena->p = new_arena;
288 }
289
290 /* Called with signals off and mutex locked */
291 static void add_thread(void)
292 {
293 struct urcu_reader *urcu_reader_reg;
294
295 if (registry_arena.len
296 < registry_arena.used + sizeof(struct urcu_reader))
297 resize_arena(&registry_arena,
298 max(registry_arena.len << 1, ARENA_INIT_ALLOC));
299 /*
300 * Find a free spot.
301 */
302 for (urcu_reader_reg = registry_arena.p;
303 (void *)urcu_reader_reg < registry_arena.p + registry_arena.len;
304 urcu_reader_reg++) {
305 if (!urcu_reader_reg->alloc)
306 break;
307 }
308 urcu_reader_reg->alloc = 1;
309 registry_arena.used += sizeof(struct urcu_reader);
310
311 /* Add to registry */
312 urcu_reader_reg->tid = pthread_self();
313 assert(urcu_reader_reg->ctr == 0);
314 list_add(&urcu_reader_reg->head, &registry);
315 urcu_reader = urcu_reader_reg;
316 }
317
318 /* Called with signals off and mutex locked */
319 static void rcu_gc_registry(void)
320 {
321 struct urcu_reader *urcu_reader_reg;
322 pthread_t tid;
323 int ret;
324
325 for (urcu_reader_reg = registry_arena.p;
326 (void *)urcu_reader_reg < registry_arena.p + registry_arena.len;
327 urcu_reader_reg++) {
328 if (!urcu_reader_reg->alloc)
329 continue;
330 tid = urcu_reader_reg->tid;
331 ret = pthread_kill(tid, 0);
332 assert(ret != EINVAL);
333 if (ret == ESRCH) {
334 list_del(&urcu_reader_reg->head);
335 urcu_reader_reg->alloc = 0;
336 registry_arena.used -= sizeof(struct urcu_reader);
337 }
338 }
339 }
340
341 /* Disable signals, take mutex, add to registry */
342 void rcu_bp_register(void)
343 {
344 sigset_t newmask, oldmask;
345 int ret;
346
347 ret = sigemptyset(&newmask);
348 assert(!ret);
349 ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
350 assert(!ret);
351
352 /*
353 * Check if a signal concurrently registered our thread since
354 * the check in rcu_read_lock(). */
355 if (urcu_reader)
356 goto end;
357
358 internal_urcu_lock();
359 add_thread();
360 internal_urcu_unlock();
361 end:
362 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
363 assert(!ret);
364 }
365
366 void urcu_bp_exit()
367 {
368 munmap(registry_arena.p, registry_arena.len);
369 }
This page took 0.05555 seconds and 5 git commands to generate.