Merge branch 'master' into urcu/ht-shrink
[urcu.git] / urcu-defer-impl.h
1 #ifndef _URCU_DEFER_IMPL_H
2 #define _URCU_DEFER_IMPL_H
3
4 /*
5 * urcu-defer-impl.h
6 *
7 * Userspace RCU header - memory reclamation.
8 *
9 * TO BE INCLUDED ONLY FROM URCU LIBRARY CODE. See urcu-defer.h for linking
10 * dynamically with the userspace rcu reclamation library.
11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
14 *
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
19 *
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
24 *
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
28 *
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
30 */
31
32 #include <stdlib.h>
33 #include <pthread.h>
34 #include <stdio.h>
35 #include <signal.h>
36 #include <assert.h>
37 #include <string.h>
38 #include <errno.h>
39 #include <poll.h>
40 #include <sys/time.h>
41 #include <unistd.h>
42 #include <stdint.h>
43
44 #include "urcu/futex.h"
45
46 #include <urcu/compiler.h>
47 #include <urcu/arch.h>
48 #include <urcu/uatomic.h>
49 #include <urcu/list.h>
50 #include <urcu/system.h>
51
52 /*
53 * Number of entries in the per-thread defer queue. Must be power of 2.
54 */
55 #define DEFER_QUEUE_SIZE (1 << 12)
56 #define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
57
58 /*
59 * Typically, data is aligned at least on the architecture size.
60 * Use lowest bit to indicate that the current callback is changing.
61 * Assumes that (void *)-2L is not used often. Used to encode non-aligned
62 * functions and non-aligned data using extra space.
63 * We encode the (void *)-2L fct as: -2L, fct, data.
64 * We encode the (void *)-2L data as: -2L, fct, data.
65 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
66 */
67 #define DQ_FCT_BIT (1 << 0)
68 #define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
69 #define DQ_SET_FCT_BIT(x) \
70 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
71 #define DQ_CLEAR_FCT_BIT(x) \
72 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
73 #define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
74
75 /*
76 * This code section can only be included in LGPL 2.1 compatible source code.
77 * See below for the function call wrappers which can be used in code meant to
78 * be only linked with the Userspace RCU library. This comes with a small
79 * performance degradation on the read-side due to the added function calls.
80 * This is required to permit relinking with newer versions of the library.
81 */
82
83 #ifdef DEBUG_RCU
84 #define rcu_assert(args...) assert(args)
85 #else
86 #define rcu_assert(args...)
87 #endif
88
89 /*
90 * defer queue.
91 * Contains pointers. Encoded to save space when same callback is often used.
92 * When looking up the next item:
93 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
94 * - next element contains pointer to data.
95 * - else if item == DQ_FCT_MARK
96 * - set the current callback to next element ptr
97 * - following next element contains pointer to data.
98 * - else current element contains data
99 */
100 struct defer_queue {
101 unsigned long head; /* add element at head */
102 void *last_fct_in; /* last fct pointer encoded */
103 unsigned long tail; /* next element to remove at tail */
104 void *last_fct_out; /* last fct pointer encoded */
105 void **q;
106 /* registry information */
107 unsigned long last_head;
108 struct cds_list_head list; /* list of thread queues */
109 };
110
111 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
112 #include "urcu-defer.h"
113
114 void __attribute__((destructor)) rcu_defer_exit(void);
115
116 extern void synchronize_rcu(void);
117
118 /*
119 * rcu_defer_mutex nests inside defer_thread_mutex.
120 */
121 static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
122 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
123
124 static int32_t defer_thread_futex;
125
126 /*
127 * Written to only by each individual deferer. Read by both the deferer and
128 * the reclamation tread.
129 */
130 static struct defer_queue __thread defer_queue;
131 static CDS_LIST_HEAD(registry_defer);
132 static pthread_t tid_defer;
133
134 static void mutex_lock_defer(pthread_mutex_t *mutex)
135 {
136 int ret;
137
138 #ifndef DISTRUST_SIGNALS_EXTREME
139 ret = pthread_mutex_lock(mutex);
140 if (ret) {
141 perror("Error in pthread mutex lock");
142 exit(-1);
143 }
144 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
145 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
146 if (ret != EBUSY && ret != EINTR) {
147 printf("ret = %d, errno = %d\n", ret, errno);
148 perror("Error in pthread mutex lock");
149 exit(-1);
150 }
151 pthread_testcancel();
152 poll(NULL,0,10);
153 }
154 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
155 }
156
157 /*
158 * Wake-up any waiting defer thread. Called from many concurrent threads.
159 */
160 static void wake_up_defer(void)
161 {
162 if (unlikely(uatomic_read(&defer_thread_futex) == -1)) {
163 uatomic_set(&defer_thread_futex, 0);
164 futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
165 NULL, NULL, 0);
166 }
167 }
168
169 static unsigned long rcu_defer_num_callbacks(void)
170 {
171 unsigned long num_items = 0, head;
172 struct defer_queue *index;
173
174 mutex_lock_defer(&rcu_defer_mutex);
175 cds_list_for_each_entry(index, &registry_defer, list) {
176 head = CMM_LOAD_SHARED(index->head);
177 num_items += head - index->tail;
178 }
179 mutex_unlock(&rcu_defer_mutex);
180 return num_items;
181 }
182
183 /*
184 * Defer thread waiting. Single thread.
185 */
186 static void wait_defer(void)
187 {
188 uatomic_dec(&defer_thread_futex);
189 cmm_smp_mb(); /* Write futex before read queue */
190 if (rcu_defer_num_callbacks()) {
191 cmm_smp_mb(); /* Read queue before write futex */
192 /* Callbacks are queued, don't wait. */
193 uatomic_set(&defer_thread_futex, 0);
194 } else {
195 cmm_smp_rmb(); /* Read queue before read futex */
196 if (uatomic_read(&defer_thread_futex) == -1)
197 futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
198 NULL, NULL, 0);
199 }
200 }
201
202 /*
203 * Must be called after Q.S. is reached.
204 */
205 static void rcu_defer_barrier_queue(struct defer_queue *queue,
206 unsigned long head)
207 {
208 unsigned long i;
209 void (*fct)(void *p);
210 void *p;
211
212 /*
213 * Tail is only modified when lock is held.
214 * Head is only modified by owner thread.
215 */
216
217 for (i = queue->tail; i != head;) {
218 cmm_smp_rmb(); /* read head before q[]. */
219 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
220 if (unlikely(DQ_IS_FCT_BIT(p))) {
221 DQ_CLEAR_FCT_BIT(p);
222 queue->last_fct_out = p;
223 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
224 } else if (unlikely(p == DQ_FCT_MARK)) {
225 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
226 queue->last_fct_out = p;
227 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
228 }
229 fct = queue->last_fct_out;
230 fct(p);
231 }
232 cmm_smp_mb(); /* push tail after having used q[] */
233 CMM_STORE_SHARED(queue->tail, i);
234 }
235
236 static void _rcu_defer_barrier_thread(void)
237 {
238 unsigned long head, num_items;
239
240 head = defer_queue.head;
241 num_items = head - defer_queue.tail;
242 if (unlikely(!num_items))
243 return;
244 synchronize_rcu();
245 rcu_defer_barrier_queue(&defer_queue, head);
246 }
247
248 void rcu_defer_barrier_thread(void)
249 {
250 mutex_lock_defer(&rcu_defer_mutex);
251 _rcu_defer_barrier_thread();
252 mutex_unlock(&rcu_defer_mutex);
253 }
254
255 /*
256 * rcu_defer_barrier - Execute all queued rcu callbacks.
257 *
258 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
259 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
260 * are guaranteed to be executed.
261 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
262 * execution are not guaranteed to be executed in the current batch (could
263 * be left for the next batch). These callbacks queued by other threads are only
264 * guaranteed to be executed if there is explicit synchronization between
265 * the thread adding to the queue and the thread issuing the defer_barrier call.
266 */
267
268 void rcu_defer_barrier(void)
269 {
270 struct defer_queue *index;
271 unsigned long num_items = 0;
272
273 if (cds_list_empty(&registry_defer))
274 return;
275
276 mutex_lock_defer(&rcu_defer_mutex);
277 cds_list_for_each_entry(index, &registry_defer, list) {
278 index->last_head = CMM_LOAD_SHARED(index->head);
279 num_items += index->last_head - index->tail;
280 }
281 if (likely(!num_items)) {
282 /*
283 * We skip the grace period because there are no queued
284 * callbacks to execute.
285 */
286 goto end;
287 }
288 synchronize_rcu();
289 cds_list_for_each_entry(index, &registry_defer, list)
290 rcu_defer_barrier_queue(index, index->last_head);
291 end:
292 mutex_unlock(&rcu_defer_mutex);
293 }
294
295 /*
296 * _defer_rcu - Queue a RCU callback.
297 */
298 void _defer_rcu(void (*fct)(void *p), void *p)
299 {
300 unsigned long head, tail;
301
302 /*
303 * Head is only modified by ourself. Tail can be modified by reclamation
304 * thread.
305 */
306 head = defer_queue.head;
307 tail = CMM_LOAD_SHARED(defer_queue.tail);
308
309 /*
310 * If queue is full, or reached threshold. Empty queue ourself.
311 * Worse-case: must allow 2 supplementary entries for fct pointer.
312 */
313 if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
314 assert(head - tail <= DEFER_QUEUE_SIZE);
315 rcu_defer_barrier_thread();
316 assert(head - CMM_LOAD_SHARED(defer_queue.tail) == 0);
317 }
318
319 if (unlikely(defer_queue.last_fct_in != fct)) {
320 defer_queue.last_fct_in = fct;
321 if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
322 /*
323 * If the function to encode is not aligned or the
324 * marker, write DQ_FCT_MARK followed by the function
325 * pointer.
326 */
327 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
328 DQ_FCT_MARK);
329 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
330 fct);
331 } else {
332 DQ_SET_FCT_BIT(fct);
333 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
334 fct);
335 }
336 } else {
337 if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
338 /*
339 * If the data to encode is not aligned or the marker,
340 * write DQ_FCT_MARK followed by the function pointer.
341 */
342 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
343 DQ_FCT_MARK);
344 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
345 fct);
346 }
347 }
348 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
349 cmm_smp_wmb(); /* Publish new pointer before head */
350 /* Write q[] before head. */
351 CMM_STORE_SHARED(defer_queue.head, head);
352 cmm_smp_mb(); /* Write queue head before read futex */
353 /*
354 * Wake-up any waiting defer thread.
355 */
356 wake_up_defer();
357 }
358
359 void *thr_defer(void *args)
360 {
361 for (;;) {
362 pthread_testcancel();
363 /*
364 * "Be green". Don't wake up the CPU if there is no RCU work
365 * to perform whatsoever. Aims at saving laptop battery life by
366 * leaving the processor in sleep state when idle.
367 */
368 wait_defer();
369 /* Sleeping after wait_defer to let many callbacks enqueue */
370 poll(NULL,0,100); /* wait for 100ms */
371 rcu_defer_barrier();
372 }
373
374 return NULL;
375 }
376
377 /*
378 * library wrappers to be used by non-LGPL compatible source code.
379 */
380
381 void defer_rcu(void (*fct)(void *p), void *p)
382 {
383 _defer_rcu(fct, p);
384 }
385
386 static void start_defer_thread(void)
387 {
388 int ret;
389
390 ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
391 assert(!ret);
392 }
393
394 static void stop_defer_thread(void)
395 {
396 int ret;
397 void *tret;
398
399 pthread_cancel(tid_defer);
400 wake_up_defer();
401 ret = pthread_join(tid_defer, &tret);
402 assert(!ret);
403 }
404
405 int rcu_defer_register_thread(void)
406 {
407 int was_empty;
408
409 assert(defer_queue.last_head == 0);
410 assert(defer_queue.q == NULL);
411 defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
412 if (!defer_queue.q)
413 return -ENOMEM;
414
415 mutex_lock_defer(&defer_thread_mutex);
416 mutex_lock_defer(&rcu_defer_mutex);
417 was_empty = cds_list_empty(&registry_defer);
418 cds_list_add(&defer_queue.list, &registry_defer);
419 mutex_unlock(&rcu_defer_mutex);
420
421 if (was_empty)
422 start_defer_thread();
423 mutex_unlock(&defer_thread_mutex);
424 return 0;
425 }
426
427 void rcu_defer_unregister_thread(void)
428 {
429 int is_empty;
430
431 mutex_lock_defer(&defer_thread_mutex);
432 mutex_lock_defer(&rcu_defer_mutex);
433 cds_list_del(&defer_queue.list);
434 _rcu_defer_barrier_thread();
435 free(defer_queue.q);
436 defer_queue.q = NULL;
437 is_empty = cds_list_empty(&registry_defer);
438 mutex_unlock(&rcu_defer_mutex);
439
440 if (is_empty)
441 stop_defer_thread();
442 mutex_unlock(&defer_thread_mutex);
443 }
444
445 void rcu_defer_exit(void)
446 {
447 assert(cds_list_empty(&registry_defer));
448 }
449
450 #endif /* _URCU_DEFER_IMPL_H */
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