uatomic compat: complete i386 support
[urcu.git] / urcu-defer.c
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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>
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31#include <sys/time.h>
32#include <syscall.h>
33#include <unistd.h>
786ee85b 34
0854ccff 35#include "urcu/urcu-futex.h"
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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
40void __attribute__((destructor)) urcu_defer_exit(void);
41
42extern void synchronize_rcu(void);
43
44/*
45 * urcu_defer_mutex nests inside defer_thread_mutex.
46 */
47static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
48static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
49
3dce4bfa 50static int defer_thread_futex;
4ce9e4f2 51
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52/*
53 * Written to only by each individual deferer. Read by both the deferer and
54 * the reclamation tread.
55 */
3dce4bfa 56static struct defer_queue __thread defer_queue;
dbc6128f 57static LIST_HEAD(registry);
786ee85b 58static pthread_t tid_defer;
4ce9e4f2 59
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60static void internal_urcu_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 }
4ce9e4f2 77 pthread_testcancel();
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78 poll(NULL,0,10);
79 }
80#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
81}
82
83static void internal_urcu_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
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94/*
95 * Wake-up any waiting defer thread. Called from many concurrent threads.
96 */
97static void wake_up_defer(void)
98{
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99 if (unlikely(uatomic_read(&defer_thread_futex) == -1)) {
100 uatomic_set(&defer_thread_futex, 0);
0854ccff 101 futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
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102 NULL, NULL, 0);
103 }
104}
105
106static unsigned long rcu_defer_num_callbacks(void)
107{
108 unsigned long num_items = 0, head;
dbc6128f 109 struct defer_queue *index;
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110
111 internal_urcu_lock(&urcu_defer_mutex);
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112 list_for_each_entry(index, &registry, list) {
113 head = LOAD_SHARED(index->head);
114 num_items += head - index->tail;
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115 }
116 internal_urcu_unlock(&urcu_defer_mutex);
117 return num_items;
118}
119
120/*
121 * Defer thread waiting. Single thread.
122 */
123static void wait_defer(void)
124{
ec4e58a3 125 uatomic_dec(&defer_thread_futex);
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126 smp_mb(); /* Write futex before read queue */
127 if (rcu_defer_num_callbacks()) {
128 smp_mb(); /* Read queue before write futex */
129 /* Callbacks are queued, don't wait. */
ec4e58a3 130 uatomic_set(&defer_thread_futex, 0);
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131 } else {
132 smp_rmb(); /* Read queue before read futex */
ec4e58a3 133 if (uatomic_read(&defer_thread_futex) == -1)
0854ccff 134 futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
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135 NULL, NULL, 0);
136 }
137}
138
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139/*
140 * Must be called after Q.S. is reached.
141 */
142static void rcu_defer_barrier_queue(struct defer_queue *queue,
804b4375 143 unsigned long head)
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144{
145 unsigned long i;
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146 void (*fct)(void *p);
147 void *p;
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148
149 /*
150 * Tail is only modified when lock is held.
151 * Head is only modified by owner thread.
152 */
153
804b4375 154 for (i = queue->tail; i != head;) {
786ee85b 155 smp_rmb(); /* read head before q[]. */
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156 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
157 if (unlikely(DQ_IS_FCT_BIT(p))) {
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158 DQ_CLEAR_FCT_BIT(p);
159 queue->last_fct_out = p;
160 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
161 } else if (unlikely(p == DQ_FCT_MARK)) {
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162 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
163 queue->last_fct_out = p;
164 p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
29cdb8d8 165 }
804b4375 166 fct = queue->last_fct_out;
804b4375 167 fct(p);
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168 }
169 smp_mb(); /* push tail after having used q[] */
170 STORE_SHARED(queue->tail, i);
171}
172
173static void _rcu_defer_barrier_thread(void)
174{
0d0e6c21 175 unsigned long head, num_items;
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176
177 head = defer_queue.head;
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178 num_items = head - defer_queue.tail;
179 if (unlikely(!num_items))
180 return;
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181 synchronize_rcu();
182 rcu_defer_barrier_queue(&defer_queue, head);
183}
184
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185void rcu_defer_barrier_thread(void)
186{
187 internal_urcu_lock(&urcu_defer_mutex);
188 _rcu_defer_barrier_thread();
189 internal_urcu_unlock(&urcu_defer_mutex);
190}
191
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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
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205void rcu_defer_barrier(void)
206{
dbc6128f 207 struct defer_queue *index;
0d0e6c21 208 unsigned long num_items = 0;
786ee85b 209
dbc6128f 210 if (list_empty(&registry))
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211 return;
212
213 internal_urcu_lock(&urcu_defer_mutex);
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214 list_for_each_entry(index, &registry, list) {
215 index->last_head = LOAD_SHARED(index->head);
216 num_items += index->last_head - index->tail;
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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 }
786ee85b 225 synchronize_rcu();
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226 list_for_each_entry(index, &registry, list)
227 rcu_defer_barrier_queue(index, index->last_head);
0d0e6c21 228end:
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229 internal_urcu_unlock(&urcu_defer_mutex);
230}
231
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232/*
233 * _rcu_defer_queue - Queue a RCU callback.
234 */
235void _rcu_defer_queue(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 = LOAD_SHARED(defer_queue.tail);
245
246 /*
247 * If queue is full, empty it 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 - 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 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
265 DQ_FCT_MARK);
266 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
267 fct);
268 } else {
269 DQ_SET_FCT_BIT(fct);
270 _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 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
280 DQ_FCT_MARK);
281 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
282 fct);
283 }
284 }
285 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
286 smp_wmb(); /* Publish new pointer before head */
287 /* Write q[] before head. */
288 STORE_SHARED(defer_queue.head, head);
04eb9c4f 289 smp_mb(); /* Write queue head before read futex */
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290 /*
291 * Wake-up any waiting defer thread.
292 */
293 wake_up_defer();
294}
295
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296void *thr_defer(void *args)
297{
298 for (;;) {
4ce9e4f2 299 pthread_testcancel();
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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 */
4ce9e4f2 305 wait_defer();
4ce9e4f2 306 /* Sleeping after wait_defer to let many callbacks enqueue */
71df5ef4 307 poll(NULL,0,100); /* wait for 100ms */
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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
804b4375 318void rcu_defer_queue(void (*fct)(void *p), void *p)
786ee85b 319{
804b4375 320 _rcu_defer_queue(fct, p);
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321}
322
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323static void start_defer_thread(void)
324{
325 int ret;
326
dbc6128f 327 ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
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328 assert(!ret);
329}
330
331static void stop_defer_thread(void)
332{
333 int ret;
334 void *tret;
335
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336 pthread_cancel(tid_defer);
337 wake_up_defer();
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338 ret = pthread_join(tid_defer, &tret);
339 assert(!ret);
340}
341
342void rcu_defer_register_thread(void)
343{
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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);
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349
350 internal_urcu_lock(&defer_thread_mutex);
351 internal_urcu_lock(&urcu_defer_mutex);
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352 was_empty = list_empty(&registry);
353 list_add(&defer_queue.list, &registry);
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354 internal_urcu_unlock(&urcu_defer_mutex);
355
dbc6128f 356 if (was_empty)
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357 start_defer_thread();
358 internal_urcu_unlock(&defer_thread_mutex);
359}
360
361void rcu_defer_unregister_thread(void)
362{
dbc6128f 363 int is_empty;
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364
365 internal_urcu_lock(&defer_thread_mutex);
366 internal_urcu_lock(&urcu_defer_mutex);
dbc6128f 367 list_del(&defer_queue.list);
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368 _rcu_defer_barrier_thread();
369 free(defer_queue.q);
370 defer_queue.q = NULL;
dbc6128f 371 is_empty = list_empty(&registry);
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372 internal_urcu_unlock(&urcu_defer_mutex);
373
dbc6128f 374 if (is_empty)
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375 stop_defer_thread();
376 internal_urcu_unlock(&defer_thread_mutex);
377}
378
379void urcu_defer_exit(void)
380{
dbc6128f 381 assert(list_empty(&registry));
786ee85b 382}
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