Fix tests makefile
[urcu.git] / urcu-defer.c
1 /*
2 * urcu-defer.c
3 *
4 * Userspace RCU library - batch memory reclamation
5 *
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
7 *
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 */
22
23 #include <stdio.h>
24 #include <pthread.h>
25 #include <signal.h>
26 #include <assert.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <errno.h>
30 #include <poll.h>
31 #include <sys/time.h>
32 #include <syscall.h>
33 #include <unistd.h>
34
35 #include "urcu-defer-static.h"
36 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
37 #include "urcu-defer.h"
38
39 #define futex(...) syscall(__NR_futex, __VA_ARGS__)
40 #define FUTEX_WAIT 0
41 #define FUTEX_WAKE 1
42
43 void __attribute__((destructor)) urcu_defer_exit(void);
44
45 extern void synchronize_rcu(void);
46
47 /*
48 * urcu_defer_mutex nests inside defer_thread_mutex.
49 */
50 static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
51 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
52
53 static int defer_thread_futex;
54
55 /*
56 * Written to only by each individual deferer. Read by both the deferer and
57 * the reclamation tread.
58 */
59 static struct defer_queue __thread defer_queue;
60 static LIST_HEAD(registry);
61 static pthread_t tid_defer;
62
63 static void internal_urcu_lock(pthread_mutex_t *mutex)
64 {
65 int ret;
66
67 #ifndef DISTRUST_SIGNALS_EXTREME
68 ret = pthread_mutex_lock(mutex);
69 if (ret) {
70 perror("Error in pthread mutex lock");
71 exit(-1);
72 }
73 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
74 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
75 if (ret != EBUSY && ret != EINTR) {
76 printf("ret = %d, errno = %d\n", ret, errno);
77 perror("Error in pthread mutex lock");
78 exit(-1);
79 }
80 pthread_testcancel();
81 poll(NULL,0,10);
82 }
83 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
84 }
85
86 static void internal_urcu_unlock(pthread_mutex_t *mutex)
87 {
88 int ret;
89
90 ret = pthread_mutex_unlock(mutex);
91 if (ret) {
92 perror("Error in pthread mutex unlock");
93 exit(-1);
94 }
95 }
96
97 /*
98 * Wake-up any waiting defer thread. Called from many concurrent threads.
99 */
100 static void wake_up_defer(void)
101 {
102 if (unlikely(uatomic_read(&defer_thread_futex) == -1)) {
103 uatomic_set(&defer_thread_futex, 0);
104 futex(&defer_thread_futex, FUTEX_WAKE, 1,
105 NULL, NULL, 0);
106 }
107 }
108
109 static unsigned long rcu_defer_num_callbacks(void)
110 {
111 unsigned long num_items = 0, head;
112 struct defer_queue *index;
113
114 internal_urcu_lock(&urcu_defer_mutex);
115 list_for_each_entry(index, &registry, list) {
116 head = LOAD_SHARED(index->head);
117 num_items += head - index->tail;
118 }
119 internal_urcu_unlock(&urcu_defer_mutex);
120 return num_items;
121 }
122
123 /*
124 * Defer thread waiting. Single thread.
125 */
126 static void wait_defer(void)
127 {
128 uatomic_dec(&defer_thread_futex);
129 smp_mb(); /* Write futex before read queue */
130 if (rcu_defer_num_callbacks()) {
131 smp_mb(); /* Read queue before write futex */
132 /* Callbacks are queued, don't wait. */
133 uatomic_set(&defer_thread_futex, 0);
134 } else {
135 smp_rmb(); /* Read queue before read futex */
136 if (uatomic_read(&defer_thread_futex) == -1)
137 futex(&defer_thread_futex, FUTEX_WAIT, -1,
138 NULL, NULL, 0);
139 }
140 }
141
142 /*
143 * Must be called after Q.S. is reached.
144 */
145 static void rcu_defer_barrier_queue(struct defer_queue *queue,
146 unsigned long head)
147 {
148 unsigned long i;
149 void (*fct)(void *p);
150 void *p;
151
152 /*
153 * Tail is only modified when lock is held.
154 * Head is only modified by owner thread.
155 */
156
157 for (i = queue->tail; i != head;) {
158 smp_rmb(); /* read head before q[]. */
159 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
160 if (unlikely(DQ_IS_FCT_BIT(p))) {
161 DQ_CLEAR_FCT_BIT(p);
162 queue->last_fct_out = p;
163 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
164 } else if (unlikely(p == DQ_FCT_MARK)) {
165 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
166 queue->last_fct_out = p;
167 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
168 }
169 fct = queue->last_fct_out;
170 fct(p);
171 }
172 smp_mb(); /* push tail after having used q[] */
173 STORE_SHARED(queue->tail, i);
174 }
175
176 static void _rcu_defer_barrier_thread(void)
177 {
178 unsigned long head, num_items;
179
180 head = defer_queue.head;
181 num_items = head - defer_queue.tail;
182 if (unlikely(!num_items))
183 return;
184 synchronize_rcu();
185 rcu_defer_barrier_queue(&defer_queue, head);
186 }
187
188 void rcu_defer_barrier_thread(void)
189 {
190 internal_urcu_lock(&urcu_defer_mutex);
191 _rcu_defer_barrier_thread();
192 internal_urcu_unlock(&urcu_defer_mutex);
193 }
194
195 /*
196 * rcu_defer_barrier - Execute all queued rcu callbacks.
197 *
198 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
199 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
200 * are guaranteed to be executed.
201 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
202 * execution are not guaranteed to be executed in the current batch (could
203 * be left for the next batch). These callbacks queued by other threads are only
204 * guaranteed to be executed if there is explicit synchronization between
205 * the thread adding to the queue and the thread issuing the defer_barrier call.
206 */
207
208 void rcu_defer_barrier(void)
209 {
210 struct defer_queue *index;
211 unsigned long num_items = 0;
212
213 if (list_empty(&registry))
214 return;
215
216 internal_urcu_lock(&urcu_defer_mutex);
217 list_for_each_entry(index, &registry, list) {
218 index->last_head = LOAD_SHARED(index->head);
219 num_items += index->last_head - index->tail;
220 }
221 if (likely(!num_items)) {
222 /*
223 * We skip the grace period because there are no queued
224 * callbacks to execute.
225 */
226 goto end;
227 }
228 synchronize_rcu();
229 list_for_each_entry(index, &registry, list)
230 rcu_defer_barrier_queue(index, index->last_head);
231 end:
232 internal_urcu_unlock(&urcu_defer_mutex);
233 }
234
235 /*
236 * _rcu_defer_queue - Queue a RCU callback.
237 */
238 void _rcu_defer_queue(void (*fct)(void *p), void *p)
239 {
240 unsigned long head, tail;
241
242 /*
243 * Head is only modified by ourself. Tail can be modified by reclamation
244 * thread.
245 */
246 head = defer_queue.head;
247 tail = LOAD_SHARED(defer_queue.tail);
248
249 /*
250 * If queue is full, empty it ourself.
251 * Worse-case: must allow 2 supplementary entries for fct pointer.
252 */
253 if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
254 assert(head - tail <= DEFER_QUEUE_SIZE);
255 rcu_defer_barrier_thread();
256 assert(head - LOAD_SHARED(defer_queue.tail) == 0);
257 }
258
259 if (unlikely(defer_queue.last_fct_in != fct)) {
260 defer_queue.last_fct_in = fct;
261 if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
262 /*
263 * If the function to encode is not aligned or the
264 * marker, write DQ_FCT_MARK followed by the function
265 * pointer.
266 */
267 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
268 DQ_FCT_MARK);
269 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
270 fct);
271 } else {
272 DQ_SET_FCT_BIT(fct);
273 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
274 fct);
275 }
276 } else {
277 if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
278 /*
279 * If the data to encode is not aligned or the marker,
280 * write DQ_FCT_MARK followed by the function pointer.
281 */
282 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
283 DQ_FCT_MARK);
284 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
285 fct);
286 }
287 }
288 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
289 smp_wmb(); /* Publish new pointer before head */
290 /* Write q[] before head. */
291 STORE_SHARED(defer_queue.head, head);
292 smp_mb(); /* Write queue head before read futex */
293 /*
294 * Wake-up any waiting defer thread.
295 */
296 wake_up_defer();
297 }
298
299 void *thr_defer(void *args)
300 {
301 for (;;) {
302 pthread_testcancel();
303 /*
304 * "Be green". Don't wake up the CPU if there is no RCU work
305 * to perform whatsoever. Aims at saving laptop battery life by
306 * leaving the processor in sleep state when idle.
307 */
308 wait_defer();
309 /* Sleeping after wait_defer to let many callbacks enqueue */
310 poll(NULL,0,100); /* wait for 100ms */
311 rcu_defer_barrier();
312 }
313
314 return NULL;
315 }
316
317 /*
318 * library wrappers to be used by non-LGPL compatible source code.
319 */
320
321 void rcu_defer_queue(void (*fct)(void *p), void *p)
322 {
323 _rcu_defer_queue(fct, p);
324 }
325
326 static void start_defer_thread(void)
327 {
328 int ret;
329
330 ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
331 assert(!ret);
332 }
333
334 static void stop_defer_thread(void)
335 {
336 int ret;
337 void *tret;
338
339 pthread_cancel(tid_defer);
340 wake_up_defer();
341 ret = pthread_join(tid_defer, &tret);
342 assert(!ret);
343 }
344
345 void rcu_defer_register_thread(void)
346 {
347 int was_empty;
348
349 assert(defer_queue.last_head == 0);
350 assert(defer_queue.q == NULL);
351 defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
352
353 internal_urcu_lock(&defer_thread_mutex);
354 internal_urcu_lock(&urcu_defer_mutex);
355 was_empty = list_empty(&registry);
356 list_add(&defer_queue.list, &registry);
357 internal_urcu_unlock(&urcu_defer_mutex);
358
359 if (was_empty)
360 start_defer_thread();
361 internal_urcu_unlock(&defer_thread_mutex);
362 }
363
364 void rcu_defer_unregister_thread(void)
365 {
366 int is_empty;
367
368 internal_urcu_lock(&defer_thread_mutex);
369 internal_urcu_lock(&urcu_defer_mutex);
370 list_del(&defer_queue.list);
371 _rcu_defer_barrier_thread();
372 free(defer_queue.q);
373 defer_queue.q = NULL;
374 is_empty = list_empty(&registry);
375 internal_urcu_unlock(&urcu_defer_mutex);
376
377 if (is_empty)
378 stop_defer_thread();
379 internal_urcu_unlock(&defer_thread_mutex);
380 }
381
382 void urcu_defer_exit(void)
383 {
384 assert(list_empty(&registry));
385 }
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