urcu-defer: handle malloc error value
[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@efficios.com>
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/urcu-futex.h"
36 #include "urcu-defer-static.h"
37 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
38 #include "urcu-defer.h"
39
40 void __attribute__((destructor)) rcu_defer_exit(void);
41
42 extern void synchronize_rcu(void);
43
44 /*
45 * rcu_defer_mutex nests inside defer_thread_mutex.
46 */
47 static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
48 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
49
50 static int defer_thread_futex;
51
52 /*
53 * Written to only by each individual deferer. Read by both the deferer and
54 * the reclamation tread.
55 */
56 static struct defer_queue __thread defer_queue;
57 static CDS_LIST_HEAD(registry);
58 static pthread_t tid_defer;
59
60 static void mutex_lock(pthread_mutex_t *mutex)
61 {
62 int ret;
63
64 #ifndef DISTRUST_SIGNALS_EXTREME
65 ret = pthread_mutex_lock(mutex);
66 if (ret) {
67 perror("Error in pthread mutex lock");
68 exit(-1);
69 }
70 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
71 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
72 if (ret != EBUSY && ret != EINTR) {
73 printf("ret = %d, errno = %d\n", ret, errno);
74 perror("Error in pthread mutex lock");
75 exit(-1);
76 }
77 pthread_testcancel();
78 poll(NULL,0,10);
79 }
80 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
81 }
82
83 static void mutex_unlock(pthread_mutex_t *mutex)
84 {
85 int ret;
86
87 ret = pthread_mutex_unlock(mutex);
88 if (ret) {
89 perror("Error in pthread mutex unlock");
90 exit(-1);
91 }
92 }
93
94 /*
95 * Wake-up any waiting defer thread. Called from many concurrent threads.
96 */
97 static void wake_up_defer(void)
98 {
99 if (unlikely(uatomic_read(&defer_thread_futex) == -1)) {
100 uatomic_set(&defer_thread_futex, 0);
101 futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
102 NULL, NULL, 0);
103 }
104 }
105
106 static unsigned long rcu_defer_num_callbacks(void)
107 {
108 unsigned long num_items = 0, head;
109 struct defer_queue *index;
110
111 mutex_lock(&rcu_defer_mutex);
112 cds_list_for_each_entry(index, &registry, list) {
113 head = CMM_LOAD_SHARED(index->head);
114 num_items += head - index->tail;
115 }
116 mutex_unlock(&rcu_defer_mutex);
117 return num_items;
118 }
119
120 /*
121 * Defer thread waiting. Single thread.
122 */
123 static void wait_defer(void)
124 {
125 uatomic_dec(&defer_thread_futex);
126 cmm_smp_mb(); /* Write futex before read queue */
127 if (rcu_defer_num_callbacks()) {
128 cmm_smp_mb(); /* Read queue before write futex */
129 /* Callbacks are queued, don't wait. */
130 uatomic_set(&defer_thread_futex, 0);
131 } else {
132 cmm_smp_rmb(); /* Read queue before read futex */
133 if (uatomic_read(&defer_thread_futex) == -1)
134 futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
135 NULL, NULL, 0);
136 }
137 }
138
139 /*
140 * Must be called after Q.S. is reached.
141 */
142 static void rcu_defer_barrier_queue(struct defer_queue *queue,
143 unsigned long head)
144 {
145 unsigned long i;
146 void (*fct)(void *p);
147 void *p;
148
149 /*
150 * Tail is only modified when lock is held.
151 * Head is only modified by owner thread.
152 */
153
154 for (i = queue->tail; i != head;) {
155 cmm_smp_rmb(); /* read head before q[]. */
156 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
157 if (unlikely(DQ_IS_FCT_BIT(p))) {
158 DQ_CLEAR_FCT_BIT(p);
159 queue->last_fct_out = p;
160 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
161 } else if (unlikely(p == DQ_FCT_MARK)) {
162 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
163 queue->last_fct_out = p;
164 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
165 }
166 fct = queue->last_fct_out;
167 fct(p);
168 }
169 cmm_smp_mb(); /* push tail after having used q[] */
170 CMM_STORE_SHARED(queue->tail, i);
171 }
172
173 static void _rcu_defer_barrier_thread(void)
174 {
175 unsigned long head, num_items;
176
177 head = defer_queue.head;
178 num_items = head - defer_queue.tail;
179 if (unlikely(!num_items))
180 return;
181 synchronize_rcu();
182 rcu_defer_barrier_queue(&defer_queue, head);
183 }
184
185 void rcu_defer_barrier_thread(void)
186 {
187 mutex_lock(&rcu_defer_mutex);
188 _rcu_defer_barrier_thread();
189 mutex_unlock(&rcu_defer_mutex);
190 }
191
192 /*
193 * rcu_defer_barrier - Execute all queued rcu callbacks.
194 *
195 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
196 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
197 * are guaranteed to be executed.
198 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
199 * execution are not guaranteed to be executed in the current batch (could
200 * be left for the next batch). These callbacks queued by other threads are only
201 * guaranteed to be executed if there is explicit synchronization between
202 * the thread adding to the queue and the thread issuing the defer_barrier call.
203 */
204
205 void rcu_defer_barrier(void)
206 {
207 struct defer_queue *index;
208 unsigned long num_items = 0;
209
210 if (cds_list_empty(&registry))
211 return;
212
213 mutex_lock(&rcu_defer_mutex);
214 cds_list_for_each_entry(index, &registry, list) {
215 index->last_head = CMM_LOAD_SHARED(index->head);
216 num_items += index->last_head - index->tail;
217 }
218 if (likely(!num_items)) {
219 /*
220 * We skip the grace period because there are no queued
221 * callbacks to execute.
222 */
223 goto end;
224 }
225 synchronize_rcu();
226 cds_list_for_each_entry(index, &registry, list)
227 rcu_defer_barrier_queue(index, index->last_head);
228 end:
229 mutex_unlock(&rcu_defer_mutex);
230 }
231
232 /*
233 * _defer_rcu - Queue a RCU callback.
234 */
235 void _defer_rcu(void (*fct)(void *p), void *p)
236 {
237 unsigned long head, tail;
238
239 /*
240 * Head is only modified by ourself. Tail can be modified by reclamation
241 * thread.
242 */
243 head = defer_queue.head;
244 tail = CMM_LOAD_SHARED(defer_queue.tail);
245
246 /*
247 * If queue is full, or reached threshold. Empty queue ourself.
248 * Worse-case: must allow 2 supplementary entries for fct pointer.
249 */
250 if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
251 assert(head - tail <= DEFER_QUEUE_SIZE);
252 rcu_defer_barrier_thread();
253 assert(head - CMM_LOAD_SHARED(defer_queue.tail) == 0);
254 }
255
256 if (unlikely(defer_queue.last_fct_in != fct)) {
257 defer_queue.last_fct_in = fct;
258 if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
259 /*
260 * If the function to encode is not aligned or the
261 * marker, write DQ_FCT_MARK followed by the function
262 * pointer.
263 */
264 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
265 DQ_FCT_MARK);
266 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
267 fct);
268 } else {
269 DQ_SET_FCT_BIT(fct);
270 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
271 fct);
272 }
273 } else {
274 if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
275 /*
276 * If the data to encode is not aligned or the marker,
277 * write DQ_FCT_MARK followed by the function pointer.
278 */
279 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
280 DQ_FCT_MARK);
281 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
282 fct);
283 }
284 }
285 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
286 cmm_smp_wmb(); /* Publish new pointer before head */
287 /* Write q[] before head. */
288 CMM_STORE_SHARED(defer_queue.head, head);
289 cmm_smp_mb(); /* Write queue head before read futex */
290 /*
291 * Wake-up any waiting defer thread.
292 */
293 wake_up_defer();
294 }
295
296 void *thr_defer(void *args)
297 {
298 for (;;) {
299 pthread_testcancel();
300 /*
301 * "Be green". Don't wake up the CPU if there is no RCU work
302 * to perform whatsoever. Aims at saving laptop battery life by
303 * leaving the processor in sleep state when idle.
304 */
305 wait_defer();
306 /* Sleeping after wait_defer to let many callbacks enqueue */
307 poll(NULL,0,100); /* wait for 100ms */
308 rcu_defer_barrier();
309 }
310
311 return NULL;
312 }
313
314 /*
315 * library wrappers to be used by non-LGPL compatible source code.
316 */
317
318 void defer_rcu(void (*fct)(void *p), void *p)
319 {
320 _defer_rcu(fct, p);
321 }
322
323 static void start_defer_thread(void)
324 {
325 int ret;
326
327 ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
328 assert(!ret);
329 }
330
331 static void stop_defer_thread(void)
332 {
333 int ret;
334 void *tret;
335
336 pthread_cancel(tid_defer);
337 wake_up_defer();
338 ret = pthread_join(tid_defer, &tret);
339 assert(!ret);
340 }
341
342 int rcu_defer_register_thread(void)
343 {
344 int was_empty;
345
346 assert(defer_queue.last_head == 0);
347 assert(defer_queue.q == NULL);
348 defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
349 if (!defer_queue.q)
350 return -ENOMEM;
351
352 mutex_lock(&defer_thread_mutex);
353 mutex_lock(&rcu_defer_mutex);
354 was_empty = cds_list_empty(&registry);
355 cds_list_add(&defer_queue.list, &registry);
356 mutex_unlock(&rcu_defer_mutex);
357
358 if (was_empty)
359 start_defer_thread();
360 mutex_unlock(&defer_thread_mutex);
361 return 0;
362 }
363
364 void rcu_defer_unregister_thread(void)
365 {
366 int is_empty;
367
368 mutex_lock(&defer_thread_mutex);
369 mutex_lock(&rcu_defer_mutex);
370 cds_list_del(&defer_queue.list);
371 _rcu_defer_barrier_thread();
372 free(defer_queue.q);
373 defer_queue.q = NULL;
374 is_empty = cds_list_empty(&registry);
375 mutex_unlock(&rcu_defer_mutex);
376
377 if (is_empty)
378 stop_defer_thread();
379 mutex_unlock(&defer_thread_mutex);
380 }
381
382 void rcu_defer_exit(void)
383 {
384 assert(cds_list_empty(&registry));
385 }
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