epoll后端机制的实现代码在epoll.c文件中。
1 /*
2 * Copyright 2000-2007 Niels Provos <[email protected]>
3 * Copyright 2007-2012 Niels Provos, Nick Mathewson
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. The name of the author may not be used to endorse or promote products
14 * derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS‘‘ AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27 #include "event2/event-config.h"
28 #include "evconfig-private.h"
29
30 #ifdef EVENT__HAVE_EPOLL
31
32 #include <stdint.h>
33 #include <sys/types.h>
34 #include <sys/resource.h>
35 #ifdef EVENT__HAVE_SYS_TIME_H
36 #include <sys/time.h>
37 #endif
38 #include <sys/queue.h>
39 #include <sys/epoll.h>
40 #include <signal.h>
41 #include <limits.h>
42 #include <stdio.h>
43 #include <stdlib.h>
44 #include <string.h>
45 #include <unistd.h>
46 #include <errno.h>
47 #ifdef EVENT__HAVE_FCNTL_H
48 #include <fcntl.h>
49 #endif
50 #ifdef EVENT__HAVE_SYS_TIMERFD_H
51 #include <sys/timerfd.h>
52 #endif
53
54 #include "event-internal.h"
55 #include "evsignal-internal.h"
56 #include "event2/thread.h"
57 #include "evthread-internal.h"
58 #include "log-internal.h"
59 #include "evmap-internal.h"
60 #include "changelist-internal.h"
61 #include "time-internal.h"
62
63 /* Since Linux 2.6.17, epoll is able to report about peer half-closed connection
64 using special EPOLLRDHUP flag on a read event.
65 */
66 #if !defined(EPOLLRDHUP)
67 #define EPOLLRDHUP 0
68 #define EARLY_CLOSE_IF_HAVE_RDHUP 0
69 #else
70 #define EARLY_CLOSE_IF_HAVE_RDHUP EV_FEATURE_EARLY_CLOSE
71 #endif
72
73 #include "epolltable-internal.h"
74
75 #if defined(EVENT__HAVE_SYS_TIMERFD_H) && 76 defined(EVENT__HAVE_TIMERFD_CREATE) && 77 defined(HAVE_POSIX_MONOTONIC) && defined(TFD_NONBLOCK) && 78 defined(TFD_CLOEXEC)
79 /* Note that we only use timerfd if TFD_NONBLOCK and TFD_CLOEXEC are available
80 and working. This means that we can‘t support it on 2.6.25 (where timerfd
81 was introduced) or 2.6.26, since 2.6.27 introduced those flags.
82 */
83 #define USING_TIMERFD
84 #endif
85
86 struct epollop {
87 struct epoll_event *events;
88 int nevents;
89 int epfd;
90 #ifdef USING_TIMERFD
91 int timerfd;
92 #endif
93 };
94
95 static void *epoll_init(struct event_base *);
96 static int epoll_dispatch(struct event_base *, struct timeval *);
97 static void epoll_dealloc(struct event_base *);
98
99 static const struct eventop epollops_changelist = {
100 "epoll (with changelist)",
101 epoll_init,
102 event_changelist_add_,
103 event_changelist_del_,
104 epoll_dispatch,
105 epoll_dealloc,
106 1, /* need reinit */
107 EV_FEATURE_ET|EV_FEATURE_O1| EARLY_CLOSE_IF_HAVE_RDHUP,
108 EVENT_CHANGELIST_FDINFO_SIZE
109 };
110
111
112 static int epoll_nochangelist_add(struct event_base *base, evutil_socket_t fd,
113 short old, short events, void *p);
114 static int epoll_nochangelist_del(struct event_base *base, evutil_socket_t fd,
115 short old, short events, void *p);
116
117 const struct eventop epollops = {
118 "epoll",
119 epoll_init,
120 epoll_nochangelist_add,
121 epoll_nochangelist_del,
122 epoll_dispatch,
123 epoll_dealloc,
124 1, /* need reinit */
125 EV_FEATURE_ET|EV_FEATURE_O1|EV_FEATURE_EARLY_CLOSE,
126 0
127 };
128
129 #define INITIAL_NEVENT 32
130 #define MAX_NEVENT 4096
131
132 /* On Linux kernels at least up to 2.6.24.4, epoll can‘t handle timeout
133 * values bigger than (LONG_MAX - 999ULL)/HZ. HZ in the wild can be
134 * as big as 1000, and LONG_MAX can be as small as (1<<31)-1, so the
135 * largest number of msec we can support here is 2147482. Let‘s
136 * round that down by 47 seconds.
137 */
138 #define MAX_EPOLL_TIMEOUT_MSEC (35*60*1000)
139
140 static void *
141 epoll_init(struct event_base *base)
142 {
143 int epfd = -1;
144 struct epollop *epollop;
145
146 #ifdef EVENT__HAVE_EPOLL_CREATE1
147 /* First, try the shiny new epoll_create1 interface, if we have it. */
148 epfd = epoll_create1(EPOLL_CLOEXEC);
149 #endif
150 if (epfd == -1) {
151 /* Initialize the kernel queue using the old interface. (The
152 size field is ignored since 2.6.8.) */
153 if ((epfd = epoll_create(32000)) == -1) {
154 if (errno != ENOSYS)
155 event_warn("epoll_create");
156 return (NULL);
157 }
158 evutil_make_socket_closeonexec(epfd);
159 }
160
161 if (!(epollop = mm_calloc(1, sizeof(struct epollop)))) {
162 close(epfd);
163 return (NULL);
164 }
165
166 epollop->epfd = epfd;
167
168 /* Initialize fields */
169 epollop->events = mm_calloc(INITIAL_NEVENT, sizeof(struct epoll_event));
170 if (epollop->events == NULL) {
171 mm_free(epollop);
172 close(epfd);
173 return (NULL);
174 }
175 epollop->nevents = INITIAL_NEVENT;
176
177 if ((base->flags & EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST) != 0 ||
178 ((base->flags & EVENT_BASE_FLAG_IGNORE_ENV) == 0 &&
179 evutil_getenv_("EVENT_EPOLL_USE_CHANGELIST") != NULL)) {
180
181 base->evsel = &epollops_changelist;
182 }
183
184 #ifdef USING_TIMERFD
185 /*
186 The epoll interface ordinarily gives us one-millisecond precision,
187 so on Linux it makes perfect sense to use the CLOCK_MONOTONIC_COARSE
188 timer. But when the user has set the new PRECISE_TIMER flag for an
189 event_base, we can try to use timerfd to give them finer granularity.
190 */
191 if ((base->flags & EVENT_BASE_FLAG_PRECISE_TIMER) &&
192 base->monotonic_timer.monotonic_clock == CLOCK_MONOTONIC) {
193 int fd;
194 fd = epollop->timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK|TFD_CLOEXEC);
195 if (epollop->timerfd >= 0) {
196 struct epoll_event epev;
197 memset(&epev, 0, sizeof(epev));
198 epev.data.fd = epollop->timerfd;
199 epev.events = EPOLLIN;
200 if (epoll_ctl(epollop->epfd, EPOLL_CTL_ADD, fd, &epev) < 0) {
201 event_warn("epoll_ctl(timerfd)");
202 close(fd);
203 epollop->timerfd = -1;
204 }
205 } else {
206 if (errno != EINVAL && errno != ENOSYS) {
207 /* These errors probably mean that we were
208 * compiled with timerfd/TFD_* support, but
209 * we‘re running on a kernel that lacks those.
210 */
211 event_warn("timerfd_create");
212 }
213 epollop->timerfd = -1;
214 }
215 } else {
216 epollop->timerfd = -1;
217 }
218 #endif
219
220 evsig_init_(base);
221
222 return (epollop);
223 }
224
225 static const char *
226 change_to_string(int change)
227 {
228 change &= (EV_CHANGE_ADD|EV_CHANGE_DEL);
229 if (change == EV_CHANGE_ADD) {
230 return "add";
231 } else if (change == EV_CHANGE_DEL) {
232 return "del";
233 } else if (change == 0) {
234 return "none";
235 } else {
236 return "???";
237 }
238 }
239
240 static const char *
241 epoll_op_to_string(int op)
242 {
243 return op == EPOLL_CTL_ADD?"ADD":
244 op == EPOLL_CTL_DEL?"DEL":
245 op == EPOLL_CTL_MOD?"MOD":
246 "???";
247 }
248
249 #define PRINT_CHANGES(op, events, ch, status) 250 "Epoll %s(%d) on fd %d " status ". " 251 "Old events were %d; " 252 "read change was %d (%s); " 253 "write change was %d (%s); " 254 "close change was %d (%s)", 255 epoll_op_to_string(op), 256 events, 257 ch->fd, 258 ch->old_events, 259 ch->read_change, 260 change_to_string(ch->read_change), 261 ch->write_change, 262 change_to_string(ch->write_change), 263 ch->close_change, 264 change_to_string(ch->close_change)
265
266 static int
267 epoll_apply_one_change(struct event_base *base,
268 struct epollop *epollop,
269 const struct event_change *ch)
270 {
271 struct epoll_event epev;
272 int op, events = 0;
273 int idx;
274
275 idx = EPOLL_OP_TABLE_INDEX(ch);
276 op = epoll_op_table[idx].op;
277 events = epoll_op_table[idx].events;
278
279 if (!events) {
280 EVUTIL_ASSERT(op == 0);
281 return 0;
282 }
283
284 if ((ch->read_change|ch->write_change) & EV_CHANGE_ET)
285 events |= EPOLLET;
286
287 memset(&epev, 0, sizeof(epev));
288 epev.data.fd = ch->fd;
289 epev.events = events;
290 if (epoll_ctl(epollop->epfd, op, ch->fd, &epev) == 0) {
291 event_debug((PRINT_CHANGES(op, epev.events, ch, "okay")));
292 return 0;
293 }
294
295 switch (op) {
296 case EPOLL_CTL_MOD:
297 if (errno == ENOENT) {
298 /* If a MOD operation fails with ENOENT, the
299 * fd was probably closed and re-opened. We
300 * should retry the operation as an ADD.
301 */
302 if (epoll_ctl(epollop->epfd, EPOLL_CTL_ADD, ch->fd, &epev) == -1) {
303 event_warn("Epoll MOD(%d) on %d retried as ADD; that failed too",
304 (int)epev.events, ch->fd);
305 return -1;
306 } else {
307 event_debug(("Epoll MOD(%d) on %d retried as ADD; succeeded.",
308 (int)epev.events,
309 ch->fd));
310 return 0;
311 }
312 }
313 break;
314 case EPOLL_CTL_ADD:
315 if (errno == EEXIST) {
316 /* If an ADD operation fails with EEXIST,
317 * either the operation was redundant (as with a
318 * precautionary add), or we ran into a fun
319 * kernel bug where using dup*() to duplicate the
320 * same file into the same fd gives you the same epitem
321 * rather than a fresh one. For the second case,
322 * we must retry with MOD. */
323 if (epoll_ctl(epollop->epfd, EPOLL_CTL_MOD, ch->fd, &epev) == -1) {
324 event_warn("Epoll ADD(%d) on %d retried as MOD; that failed too",
325 (int)epev.events, ch->fd);
326 return -1;
327 } else {
328 event_debug(("Epoll ADD(%d) on %d retried as MOD; succeeded.",
329 (int)epev.events,
330 ch->fd));
331 return 0;
332 }
333 }
334 break;
335 case EPOLL_CTL_DEL:
336 if (errno == ENOENT || errno == EBADF || errno == EPERM) {
337 /* If a delete fails with one of these errors,
338 * that‘s fine too: we closed the fd before we
339 * got around to calling epoll_dispatch. */
340 event_debug(("Epoll DEL(%d) on fd %d gave %s: DEL was unnecessary.",
341 (int)epev.events,
342 ch->fd,
343 strerror(errno)));
344 return 0;
345 }
346 break;
347 default:
348 break;
349 }
350
351 event_warn(PRINT_CHANGES(op, epev.events, ch, "failed"));
352 return -1;
353 }
354
355 static int
356 epoll_apply_changes(struct event_base *base)
357 {
358 struct event_changelist *changelist = &base->changelist;
359 struct epollop *epollop = base->evbase;
360 struct event_change *ch;
361
362 int r = 0;
363 int i;
364
365 for (i = 0; i < changelist->n_changes; ++i) {
366 ch = &changelist->changes[i];
367 if (epoll_apply_one_change(base, epollop, ch) < 0)
368 r = -1;
369 }
370
371 return (r);
372 }
373
374 static int
375 epoll_nochangelist_add(struct event_base *base, evutil_socket_t fd,
376 short old, short events, void *p)
377 {
378 struct event_change ch;
379 ch.fd = fd;
380 ch.old_events = old;
381 ch.read_change = ch.write_change = ch.close_change = 0;
382 if (events & EV_WRITE)
383 ch.write_change = EV_CHANGE_ADD |
384 (events & EV_ET);
385 if (events & EV_READ)
386 ch.read_change = EV_CHANGE_ADD |
387 (events & EV_ET);
388 if (events & EV_CLOSED)
389 ch.close_change = EV_CHANGE_ADD |
390 (events & EV_ET);
391
392 return epoll_apply_one_change(base, base->evbase, &ch);
393 }
394
395 static int
396 epoll_nochangelist_del(struct event_base *base, evutil_socket_t fd,
397 short old, short events, void *p)
398 {
399 struct event_change ch;
400 ch.fd = fd;
401 ch.old_events = old;
402 ch.read_change = ch.write_change = ch.close_change = 0;
403 if (events & EV_WRITE)
404 ch.write_change = EV_CHANGE_DEL;
405 if (events & EV_READ)
406 ch.read_change = EV_CHANGE_DEL;
407 if (events & EV_CLOSED)
408 ch.close_change = EV_CHANGE_DEL;
409
410 return epoll_apply_one_change(base, base->evbase, &ch);
411 }
412
413 static int
414 epoll_dispatch(struct event_base *base, struct timeval *tv)
415 {
416 struct epollop *epollop = base->evbase;
417 struct epoll_event *events = epollop->events;
418 int i, res;
419 long timeout = -1;
420
421 #ifdef USING_TIMERFD
422 if (epollop->timerfd >= 0) {
423 struct itimerspec is;
424 is.it_interval.tv_sec = 0;
425 is.it_interval.tv_nsec = 0;
426 if (tv == NULL) {
427 /* No timeout; disarm the timer. */
428 is.it_value.tv_sec = 0;
429 is.it_value.tv_nsec = 0;
430 } else {
431 if (tv->tv_sec == 0 && tv->tv_usec == 0) {
432 /* we need to exit immediately; timerfd can‘t
433 * do that. */
434 timeout = 0;
435 }
436 is.it_value.tv_sec = tv->tv_sec;
437 is.it_value.tv_nsec = tv->tv_usec * 1000;
438 }
439 /* TODO: we could avoid unnecessary syscalls here by only
440 calling timerfd_settime when the top timeout changes, or
441 when we‘re called with a different timeval.
442 */
443 if (timerfd_settime(epollop->timerfd, 0, &is, NULL) < 0) {
444 event_warn("timerfd_settime");
445 }
446 } else
447 #endif
448 if (tv != NULL) {
449 timeout = evutil_tv_to_msec_(tv);
450 if (timeout < 0 || timeout > MAX_EPOLL_TIMEOUT_MSEC) {
451 /* Linux kernels can wait forever if the timeout is
452 * too big; see comment on MAX_EPOLL_TIMEOUT_MSEC. */
453 timeout = MAX_EPOLL_TIMEOUT_MSEC;
454 }
455 }
456
457 epoll_apply_changes(base);
458 event_changelist_remove_all_(&base->changelist, base);
459
460 EVBASE_RELEASE_LOCK(base, th_base_lock);
461
462 res = epoll_wait(epollop->epfd, events, epollop->nevents, timeout);
463
464 EVBASE_ACQUIRE_LOCK(base, th_base_lock);
465
466 if (res == -1) {
467 if (errno != EINTR) {
468 event_warn("epoll_wait");
469 return (-1);
470 }
471
472 return (0);
473 }
474
475 event_debug(("%s: epoll_wait reports %d", __func__, res));
476 EVUTIL_ASSERT(res <= epollop->nevents);
477
478 for (i = 0; i < res; i++) {
479 int what = events[i].events;
480 short ev = 0;
481 #ifdef USING_TIMERFD
482 if (events[i].data.fd == epollop->timerfd)
483 continue;
484 #endif
485
486 if (what & (EPOLLHUP|EPOLLERR)) {
487 ev = EV_READ | EV_WRITE;
488 } else {
489 if (what & EPOLLIN)
490 ev |= EV_READ;
491 if (what & EPOLLOUT)
492 ev |= EV_WRITE;
493 if (what & EPOLLRDHUP)
494 ev |= EV_CLOSED;
495 }
496
497 if (!ev)
498 continue;
499
500 evmap_io_active_(base, events[i].data.fd, ev | EV_ET);
501 }
502
503 if (res == epollop->nevents && epollop->nevents < MAX_NEVENT) {
504 /* We used all of the event space this time. We should
505 be ready for more events next time. */
506 int new_nevents = epollop->nevents * 2;
507 struct epoll_event *new_events;
508
509 new_events = mm_realloc(epollop->events,
510 new_nevents * sizeof(struct epoll_event));
511 if (new_events) {
512 epollop->events = new_events;
513 epollop->nevents = new_nevents;
514 }
515 }
516
517 return (0);
518 }
519
520
521 static void
522 epoll_dealloc(struct event_base *base)
523 {
524 struct epollop *epollop = base->evbase;
525
526 evsig_dealloc_(base);
527 if (epollop->events)
528 mm_free(epollop->events);
529 if (epollop->epfd >= 0)
530 close(epollop->epfd);
531 #ifdef USING_TIMERFD
532 if (epollop->timerfd >= 0)
533 close(epollop->timerfd);
534 #endif
535
536 memset(epollop, 0, sizeof(struct epollop));
537 mm_free(epollop);
538 }
539
540 #endif /* EVENT__HAVE_EPOLL */
(1)第117行-127行定义的epollops对应了这篇文章里说的epoll后端机制的定义。
(2)该文件中定义了epoll_init函数用于初始化、epoll_add函数用于添加一个事件、epoll_del函数用于删除一个事件、epoll_dispatch用于事件循环。
1、epoll_init函数
1）调用epoll_create创建epfd。
2）在堆上分配一个struct epollop结构epollop。
3）把epollop的成员epfd赋值为刚才创建的epfd。
4）初始化成员events，调用mm_malloc函数来分配。
5）初始化成员nevents为INITIAL_NEVENT。
6）如果定义了USING_TIMERFD宏，就初始化成员timerfd。
7）调用svsig_init_函数。
8）返回epollop。
2、epoll_nochanglist_add函数
1）判断read、write、close是否有改变。
2）调用epoll_apply_one_change函数，在该函数中首先调用epool_ctl修改事件，然后处理各种异常情况，比如：ENOENT、EEXIST等等。
3、epoll_nochangelist_del函数
1）判断read、write、close是否有删除。
2）调用函数epoll_apply_one_change函数。
4、epoll_dispatch函数
1）通过event_base结构的evbase获取epollop指针，然后获取到初始化时传入的events指针并保存在events中。
2）获取timeout。
3）调用epoll_wait函数。
4）在一个for循环中处理激活事件，在每一次循环中，先把epoll事件转换为libevent定义的事件，EPOLLIN->EV_READ，EPOLLOUT->EV_WRITE，EPOLLRDHUP->EV_CLOSED，然后调用evmap_io_active_函数。
5）判断如果用完了所有事件，则为下一次准备更多的事件，扩展为原来的2倍，第一次默认是32。
时间： 2024-08-05 19:37:40