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 either:
65 * fct | DQ_FCT_BIT, data (if fct is aligned), or
66 * -2L, fct, data (if fct is not aligned).
67 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
68 */
69 #define DQ_FCT_BIT (1 << 0)
70 #define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
71 #define DQ_SET_FCT_BIT(x) \
72 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
73 #define DQ_CLEAR_FCT_BIT(x) \
74 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
75 #define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
76
77 /*
78 * This code section can only be included in LGPL 2.1 compatible source code.
79 * See below for the function call wrappers which can be used in code meant to
80 * be only linked with the Userspace RCU library. This comes with a small
81 * performance degradation on the read-side due to the added function calls.
82 * This is required to permit relinking with newer versions of the library.
83 */
84
85 #ifdef DEBUG_RCU
86 #define rcu_assert(args...) assert(args)
87 #else
88 #define rcu_assert(args...)
89 #endif
90
91 /*
92 * defer queue.
93 * Contains pointers. Encoded to save space when same callback is often used.
94 * When looking up the next item:
95 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
96 * - next element contains pointer to data.
97 * - else if item == DQ_FCT_MARK
98 * - set the current callback to next element ptr
99 * - following next element contains pointer to data.
100 * - else current element contains data
101 */
102 struct defer_queue {
103 unsigned long head; /* add element at head */
104 void *last_fct_in; /* last fct pointer encoded */
105 unsigned long tail; /* next element to remove at tail */
106 void *last_fct_out; /* last fct pointer encoded */
107 void **q;
108 /* registry information */
109 unsigned long last_head;
110 struct cds_list_head list; /* list of thread queues */
111 };
112
113 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
114 #include "urcu-defer.h"
115
116 void __attribute__((destructor)) rcu_defer_exit(void);
117
118 extern void synchronize_rcu(void);
119
120 /*
121 * rcu_defer_mutex nests inside defer_thread_mutex.
122 */
123 static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
124 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
125
126 static int32_t defer_thread_futex;
127 static int32_t defer_thread_stop;
128
129 /*
130 * Written to only by each individual deferer. Read by both the deferer and
131 * the reclamation tread.
132 */
133 static struct defer_queue __thread defer_queue;
134 static CDS_LIST_HEAD(registry_defer);
135 static pthread_t tid_defer;
136
137 static void mutex_lock_defer(pthread_mutex_t *mutex)
138 {
139 int ret;
140
141 #ifndef DISTRUST_SIGNALS_EXTREME
142 ret = pthread_mutex_lock(mutex);
143 if (ret) {
144 perror("Error in pthread mutex lock");
145 exit(-1);
146 }
147 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
148 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
149 if (ret != EBUSY && ret != EINTR) {
150 printf("ret = %d, errno = %d\n", ret, errno);
151 perror("Error in pthread mutex lock");
152 exit(-1);
153 }
154 poll(NULL,0,10);
155 }
156 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
157 }
158
159 /*
160 * Wake-up any waiting defer thread. Called from many concurrent threads.
161 */
162 static void wake_up_defer(void)
163 {
164 if (unlikely(uatomic_read(&defer_thread_futex) == -1)) {
165 uatomic_set(&defer_thread_futex, 0);
166 futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
167 NULL, NULL, 0);
168 }
169 }
170
171 static unsigned long rcu_defer_num_callbacks(void)
172 {
173 unsigned long num_items = 0, head;
174 struct defer_queue *index;
175
176 mutex_lock_defer(&rcu_defer_mutex);
177 cds_list_for_each_entry(index, &registry_defer, list) {
178 head = CMM_LOAD_SHARED(index->head);
179 num_items += head - index->tail;
180 }
181 mutex_unlock(&rcu_defer_mutex);
182 return num_items;
183 }
184
185 /*
186 * Defer thread waiting. Single thread.
187 */
188 static void wait_defer(void)
189 {
190 uatomic_dec(&defer_thread_futex);
191 /* Write futex before read queue */
192 /* Write futex before read defer_thread_stop */
193 cmm_smp_mb();
194 if (_CMM_LOAD_SHARED(defer_thread_stop)) {
195 uatomic_set(&defer_thread_futex, 0);
196 pthread_exit(0);
197 }
198 if (rcu_defer_num_callbacks()) {
199 cmm_smp_mb(); /* Read queue before write futex */
200 /* Callbacks are queued, don't wait. */
201 uatomic_set(&defer_thread_futex, 0);
202 } else {
203 cmm_smp_rmb(); /* Read queue before read futex */
204 if (uatomic_read(&defer_thread_futex) == -1)
205 futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
206 NULL, NULL, 0);
207 }
208 }
209
210 /*
211 * Must be called after Q.S. is reached.
212 */
213 static void rcu_defer_barrier_queue(struct defer_queue *queue,
214 unsigned long head)
215 {
216 unsigned long i;
217 void (*fct)(void *p);
218 void *p;
219
220 /*
221 * Tail is only modified when lock is held.
222 * Head is only modified by owner thread.
223 */
224
225 for (i = queue->tail; i != head;) {
226 cmm_smp_rmb(); /* read head before q[]. */
227 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
228 if (unlikely(DQ_IS_FCT_BIT(p))) {
229 DQ_CLEAR_FCT_BIT(p);
230 queue->last_fct_out = p;
231 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
232 } else if (unlikely(p == DQ_FCT_MARK)) {
233 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
234 queue->last_fct_out = p;
235 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
236 }
237 fct = queue->last_fct_out;
238 fct(p);
239 }
240 cmm_smp_mb(); /* push tail after having used q[] */
241 CMM_STORE_SHARED(queue->tail, i);
242 }
243
244 static void _rcu_defer_barrier_thread(void)
245 {
246 unsigned long head, num_items;
247
248 head = defer_queue.head;
249 num_items = head - defer_queue.tail;
250 if (unlikely(!num_items))
251 return;
252 synchronize_rcu();
253 rcu_defer_barrier_queue(&defer_queue, head);
254 }
255
256 void rcu_defer_barrier_thread(void)
257 {
258 mutex_lock_defer(&rcu_defer_mutex);
259 _rcu_defer_barrier_thread();
260 mutex_unlock(&rcu_defer_mutex);
261 }
262
263 /*
264 * rcu_defer_barrier - Execute all queued rcu callbacks.
265 *
266 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
267 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
268 * are guaranteed to be executed.
269 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
270 * execution are not guaranteed to be executed in the current batch (could
271 * be left for the next batch). These callbacks queued by other threads are only
272 * guaranteed to be executed if there is explicit synchronization between
273 * the thread adding to the queue and the thread issuing the defer_barrier call.
274 */
275
276 void rcu_defer_barrier(void)
277 {
278 struct defer_queue *index;
279 unsigned long num_items = 0;
280
281 if (cds_list_empty(&registry_defer))
282 return;
283
284 mutex_lock_defer(&rcu_defer_mutex);
285 cds_list_for_each_entry(index, &registry_defer, list) {
286 index->last_head = CMM_LOAD_SHARED(index->head);
287 num_items += index->last_head - index->tail;
288 }
289 if (likely(!num_items)) {
290 /*
291 * We skip the grace period because there are no queued
292 * callbacks to execute.
293 */
294 goto end;
295 }
296 synchronize_rcu();
297 cds_list_for_each_entry(index, &registry_defer, list)
298 rcu_defer_barrier_queue(index, index->last_head);
299 end:
300 mutex_unlock(&rcu_defer_mutex);
301 }
302
303 /*
304 * _defer_rcu - Queue a RCU callback.
305 */
306 void _defer_rcu(void (*fct)(void *p), void *p)
307 {
308 unsigned long head, tail;
309
310 /*
311 * Head is only modified by ourself. Tail can be modified by reclamation
312 * thread.
313 */
314 head = defer_queue.head;
315 tail = CMM_LOAD_SHARED(defer_queue.tail);
316
317 /*
318 * If queue is full, or reached threshold. Empty queue ourself.
319 * Worse-case: must allow 2 supplementary entries for fct pointer.
320 */
321 if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
322 assert(head - tail <= DEFER_QUEUE_SIZE);
323 rcu_defer_barrier_thread();
324 assert(head - CMM_LOAD_SHARED(defer_queue.tail) == 0);
325 }
326
327 /*
328 * Encode:
329 * if the function is not changed and the data is aligned and it is
330 * not the marker:
331 * store the data
332 * otherwise if the function is aligned and its not the marker:
333 * store the function with DQ_FCT_BIT
334 * store the data
335 * otherwise:
336 * store the marker (DQ_FCT_MARK)
337 * store the function
338 * store the data
339 *
340 * Decode: see the comments before 'struct defer_queue'
341 * or the code in rcu_defer_barrier_queue().
342 */
343 if (unlikely(defer_queue.last_fct_in != fct
344 || DQ_IS_FCT_BIT(p)
345 || p == DQ_FCT_MARK)) {
346 defer_queue.last_fct_in = fct;
347 if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
348 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
349 DQ_FCT_MARK);
350 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
351 fct);
352 } else {
353 DQ_SET_FCT_BIT(fct);
354 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
355 fct);
356 }
357 }
358 _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
359 cmm_smp_wmb(); /* Publish new pointer before head */
360 /* Write q[] before head. */
361 CMM_STORE_SHARED(defer_queue.head, head);
362 cmm_smp_mb(); /* Write queue head before read futex */
363 /*
364 * Wake-up any waiting defer thread.
365 */
366 wake_up_defer();
367 }
368
369 void *thr_defer(void *args)
370 {
371 for (;;) {
372 /*
373 * "Be green". Don't wake up the CPU if there is no RCU work
374 * to perform whatsoever. Aims at saving laptop battery life by
375 * leaving the processor in sleep state when idle.
376 */
377 wait_defer();
378 /* Sleeping after wait_defer to let many callbacks enqueue */
379 poll(NULL,0,100); /* wait for 100ms */
380 rcu_defer_barrier();
381 }
382
383 return NULL;
384 }
385
386 /*
387 * library wrappers to be used by non-LGPL compatible source code.
388 */
389
390 void defer_rcu(void (*fct)(void *p), void *p)
391 {
392 _defer_rcu(fct, p);
393 }
394
395 static void start_defer_thread(void)
396 {
397 int ret;
398
399 ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
400 assert(!ret);
401 }
402
403 static void stop_defer_thread(void)
404 {
405 int ret;
406 void *tret;
407
408 _CMM_STORE_SHARED(defer_thread_stop, 1);
409 /* Store defer_thread_stop before testing futex */
410 cmm_smp_mb();
411 wake_up_defer();
412
413 ret = pthread_join(tid_defer, &tret);
414 assert(!ret);
415
416 CMM_STORE_SHARED(defer_thread_stop, 0);
417 /* defer thread should always exit when futex value is 0 */
418 assert(uatomic_read(&defer_thread_futex) == 0);
419 }
420
421 int rcu_defer_register_thread(void)
422 {
423 int was_empty;
424
425 assert(defer_queue.last_head == 0);
426 assert(defer_queue.q == NULL);
427 defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
428 if (!defer_queue.q)
429 return -ENOMEM;
430
431 mutex_lock_defer(&defer_thread_mutex);
432 mutex_lock_defer(&rcu_defer_mutex);
433 was_empty = cds_list_empty(&registry_defer);
434 cds_list_add(&defer_queue.list, &registry_defer);
435 mutex_unlock(&rcu_defer_mutex);
436
437 if (was_empty)
438 start_defer_thread();
439 mutex_unlock(&defer_thread_mutex);
440 return 0;
441 }
442
443 void rcu_defer_unregister_thread(void)
444 {
445 int is_empty;
446
447 mutex_lock_defer(&defer_thread_mutex);
448 mutex_lock_defer(&rcu_defer_mutex);
449 cds_list_del(&defer_queue.list);
450 _rcu_defer_barrier_thread();
451 free(defer_queue.q);
452 defer_queue.q = NULL;
453 is_empty = cds_list_empty(&registry_defer);
454 mutex_unlock(&rcu_defer_mutex);
455
456 if (is_empty)
457 stop_defer_thread();
458 mutex_unlock(&defer_thread_mutex);
459 }
460
461 void rcu_defer_exit(void)
462 {
463 assert(cds_list_empty(&registry_defer));
464 }
465
466 #endif /* _URCU_DEFER_IMPL_H */
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