libev/ev_epoll.c

/*
 * libev epoll fd activity backend
 *
 * Copyright (c) 2007,2008,2009,2010 Marc Alexander Lehmann <libev@schmorp.de>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modifica-
 * tion, are permitted provided that the following conditions are met:
 * 
 *   1.  Redistributions of source code must retain the above copyright notice,
 *       this list of conditions and the following disclaimer.
 * 
 *   2.  Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
 * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
 * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
 * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License ("GPL") version 2 or any later version,
 * in which case the provisions of the GPL are applicable instead of
 * the above. If you wish to allow the use of your version of this file
 * only under the terms of the GPL and not to allow others to use your
 * version of this file under the BSD license, indicate your decision
 * by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL. If you do not delete the
 * provisions above, a recipient may use your version of this file under
 * either the BSD or the GPL.
 */

/*
 * general notes about epoll:
 *
 * a) epoll silently removes fds from the fd set. as nothing tells us
 *    that an fd has been removed otherwise, we have to continually
 *    "rearm" fds that we suspect *might* have changed (same
 *    problem with kqueue, but much less costly there).
 * b) the fact that ADD != MOD creates a lot of extra syscalls due to a)
 *    and seems not to have any advantage.
 * c) the inability to handle fork or file descriptors (think dup)
 *    limits the applicability over poll, so this is not a generic
 *    poll replacement.
 * d) epoll doesn't work the same as select with many file descriptors
 *    (such as files). while not critical, no other advanced interface
 *    seems to share this (rather non-unixy) limitation.
 * e) epoll claims to be embeddable, but in practise you never get
 *    a ready event for the epoll fd.
 *
 * lots of "weird code" and complication handling in this file is due
 * to these design problems with epoll, as we try very hard to avoid
 * epoll_ctl syscalls for common usage patterns and handle the breakage
 * ensuing from receiving events for closed and otherwise long gone
 * file descriptors.
 */

#include <sys/epoll.h>

static void
epoll_modify (EV_P_ int fd, int oev, int nev)
{
  struct epoll_event ev;
  unsigned char oldmask;

  /*
   * we handle EPOLL_CTL_DEL by ignoring it here
   * on the assumption that the fd is gone anyways
   * if that is wrong, we have to handle the spurious
   * event in epoll_poll.
   * if the fd is added again, we try to ADD it, and, if that
   * fails, we assume it still has the same eventmask.
   */
  if (!nev)
    return;

  oldmask = anfds [fd].emask;
  anfds [fd].emask = nev;

  /* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */
  ev.data.u64 = (uint64_t)(uint32_t)fd
              | ((uint64_t)(uint32_t)++anfds [fd].egen << 32);
  ev.events   = (nev & EV_READ  ? EPOLLIN  : 0)
              | (nev & EV_WRITE ? EPOLLOUT : 0);

  if (expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))
    return;

  if (expect_true (errno == ENOENT))
    {
      /* if ENOENT then the fd went away, so try to do the right thing */
      if (!nev)
        goto dec_egen;

      if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))
        return;
    }
  else if (expect_true (errno == EEXIST))
    {
      /* EEXIST means we ignored a previous DEL, but the fd is still active */
      /* if the kernel mask is the same as the new mask, we assume it hasn't changed */
      if (oldmask == nev)
        goto dec_egen;

      if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))
        return;
    }

  fd_kill (EV_A_ fd);

dec_egen:
  /* we didn't successfully call epoll_ctl, so decrement the generation counter again */
  --anfds [fd].egen;
}

static void
epoll_poll (EV_P_ ev_tstamp timeout)
{
  int i;
  int eventcnt;
  
  /* epoll wait times cannot be larger than (LONG_MAX - 999UL) / HZ msecs, which is below */
  /* the default libev max wait time, however. */
  EV_RELEASE_CB;
  eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, (int)ceil (timeout * 1000.));
  EV_ACQUIRE_CB;

  if (expect_false (eventcnt < 0))
    {
      if (errno != EINTR)
        ev_syserr ("(libev) epoll_wait");

      return;
    }

  for (i = 0; i < eventcnt; ++i)
    {
      struct epoll_event *ev = epoll_events + i;

      int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */
      int want = anfds [fd].events;
      int got  = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
               | (ev->events & (EPOLLIN  | EPOLLERR | EPOLLHUP) ? EV_READ  : 0);

      /* check for spurious notification */
      if (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))
        {
          /* recreate kernel state */
          postfork = 1;
          continue;
        }

      if (expect_false (got & ~want))
        {
          anfds [fd].emask = want;

          /* we received an event but are not interested in it, try mod or del */
          /* I don't think we ever need MOD, but let's handle it anyways */
          ev->events = (want & EV_READ  ? EPOLLIN  : 0)
                     | (want & EV_WRITE ? EPOLLOUT : 0);

          /* pre-2.6.9 kernels require a non-null pointer with EPOLL_CTL_DEL, */
          /* which is fortunately easy to do for us. */
          if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev))
            {
              postfork = 1; /* an error occured, recreate kernel state */
              continue;
            }
        }

      fd_event (EV_A_ fd, got);
    }

  /* if the receive array was full, increase its size */
  if (expect_false (eventcnt == epoll_eventmax))
    {
      ev_free (epoll_events);
      epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1);
      epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);
    }
}

int inline_size
epoll_init (EV_P_ int flags)
{
#ifdef EPOLL_CLOEXEC
  backend_fd = epoll_create1 (EPOLL_CLOEXEC);

  if (backend_fd <= 0)
#endif
    backend_fd = epoll_create (256);

  if (backend_fd < 0)
    return 0;

  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);

  backend_fudge  = 0.; /* kernel sources seem to indicate this to be zero */
  backend_modify = epoll_modify;
  backend_poll   = epoll_poll;

  epoll_eventmax = 64; /* initial number of events receivable per poll */
  epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);

  return EVBACKEND_EPOLL;
}

void inline_size
epoll_destroy (EV_P)
{
  ev_free (epoll_events);
}

void inline_size
epoll_fork (EV_P)
{
  close (backend_fd);

  while ((backend_fd = epoll_create (256)) < 0)
    ev_syserr ("(libev) epoll_create");

  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);

  fd_rearm_all (EV_A);
}

Revision:	1.51
Committed:	Wed Apr 21 13:13:18 2010 UTC (14 years ago) by root
Content type:	text/plain
Branch:	MAIN
Changes since 1.50:	+1 -1 lines
Log Message:	* empty log message *
#	Content
1	/*
2	* libev epoll fd activity backend
3	*
4	* Copyright (c) 2007,2008,2009,2010 Marc Alexander Lehmann <libev@schmorp.de>
5	* All rights reserved.
6	*
7	* Redistribution and use in source and binary forms, with or without modifica-
8	* tion, are permitted provided that the following conditions are met:
9	*
10	* 1. Redistributions of source code must retain the above copyright notice,
11	* this list of conditions and the following disclaimer.
12	*
13	* 2. Redistributions in binary form must reproduce the above copyright
14	* notice, this list of conditions and the following disclaimer in the
15	* documentation and/or other materials provided with the distribution.
16	*
17	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
18	* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
19	* CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
20	* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
21	* CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
23	* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
24	* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
25	* ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
26	* OF THE POSSIBILITY OF SUCH DAMAGE.
27	*
28	* Alternatively, the contents of this file may be used under the terms of
29	* the GNU General Public License ("GPL") version 2 or any later version,
30	* in which case the provisions of the GPL are applicable instead of
31	* the above. If you wish to allow the use of your version of this file
32	* only under the terms of the GPL and not to allow others to use your
33	* version of this file under the BSD license, indicate your decision
34	* by deleting the provisions above and replace them with the notice
35	* and other provisions required by the GPL. If you do not delete the
36	* provisions above, a recipient may use your version of this file under
37	* either the BSD or the GPL.
38	*/
39
40	/*
41	* general notes about epoll:
42	*
43	* a) epoll silently removes fds from the fd set. as nothing tells us
44	* that an fd has been removed otherwise, we have to continually
45	* "rearm" fds that we suspect might have changed (same
46	* problem with kqueue, but much less costly there).
47	* b) the fact that ADD != MOD creates a lot of extra syscalls due to a)
48	* and seems not to have any advantage.
49	* c) the inability to handle fork or file descriptors (think dup)
50	* limits the applicability over poll, so this is not a generic
51	* poll replacement.
52	* d) epoll doesn't work the same as select with many file descriptors
53	* (such as files). while not critical, no other advanced interface
54	* seems to share this (rather non-unixy) limitation.
55	* e) epoll claims to be embeddable, but in practise you never get
56	* a ready event for the epoll fd.
57	*
58	* lots of "weird code" and complication handling in this file is due
59	* to these design problems with epoll, as we try very hard to avoid
60	* epoll_ctl syscalls for common usage patterns and handle the breakage
61	* ensuing from receiving events for closed and otherwise long gone
62	* file descriptors.
63	*/
64
65	#include <sys/epoll.h>
66
67	static void
68	epoll_modify (EV_P_ int fd, int oev, int nev)
69	{
70	struct epoll_event ev;
71	unsigned char oldmask;
72
73	/*
74	* we handle EPOLL_CTL_DEL by ignoring it here
75	* on the assumption that the fd is gone anyways
76	* if that is wrong, we have to handle the spurious
77	* event in epoll_poll.
78	* if the fd is added again, we try to ADD it, and, if that
79	* fails, we assume it still has the same eventmask.
80	*/
81	if (!nev)
82	return;
83
84	oldmask = anfds [fd].emask;
85	anfds [fd].emask = nev;
86
87	/* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */
88	ev.data.u64 = (uint64_t)(uint32_t)fd
89	\| ((uint64_t)(uint32_t)++anfds [fd].egen << 32);
90	ev.events = (nev & EV_READ ? EPOLLIN : 0)
91	\| (nev & EV_WRITE ? EPOLLOUT : 0);
92
93	if (expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))
94	return;
95
96	if (expect_true (errno == ENOENT))
97	{
98	/* if ENOENT then the fd went away, so try to do the right thing */
99	if (!nev)
100	goto dec_egen;
101
102	if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))
103	return;
104	}
105	else if (expect_true (errno == EEXIST))
106	{
107	/* EEXIST means we ignored a previous DEL, but the fd is still active */
108	/* if the kernel mask is the same as the new mask, we assume it hasn't changed */
109	if (oldmask == nev)
110	goto dec_egen;
111
112	if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))
113	return;
114	}
115
116	fd_kill (EV_A_ fd);
117
118	dec_egen:
119	/* we didn't successfully call epoll_ctl, so decrement the generation counter again */
120	--anfds [fd].egen;
121	}
122
123	static void
124	epoll_poll (EV_P_ ev_tstamp timeout)
125	{
126	int i;
127	int eventcnt;
128
129	/* epoll wait times cannot be larger than (LONG_MAX - 999UL) / HZ msecs, which is below */
130	/* the default libev max wait time, however. */
131	EV_RELEASE_CB;
132	eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, (int)ceil (timeout * 1000.));
133	EV_ACQUIRE_CB;
134
135	if (expect_false (eventcnt < 0))
136	{
137	if (errno != EINTR)
138	ev_syserr ("(libev) epoll_wait");
139
140	return;
141	}
142
143	for (i = 0; i < eventcnt; ++i)
144	{
145	struct epoll_event *ev = epoll_events + i;
146
147	int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */
148	int want = anfds [fd].events;
149	int got = (ev->events & (EPOLLOUT \| EPOLLERR \| EPOLLHUP) ? EV_WRITE : 0)
150	\| (ev->events & (EPOLLIN \| EPOLLERR \| EPOLLHUP) ? EV_READ : 0);
151
152	/* check for spurious notification */
153	if (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))
154	{
155	/* recreate kernel state */
156	postfork = 1;
157	continue;
158	}
159
160	if (expect_false (got & ~want))
161	{
162	anfds [fd].emask = want;
163
164	/* we received an event but are not interested in it, try mod or del */
165	/* I don't think we ever need MOD, but let's handle it anyways */
166	ev->events = (want & EV_READ ? EPOLLIN : 0)
167	\| (want & EV_WRITE ? EPOLLOUT : 0);
168
169	/* pre-2.6.9 kernels require a non-null pointer with EPOLL_CTL_DEL, */
170	/* which is fortunately easy to do for us. */
171	if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev))
172	{
173	postfork = 1; /* an error occured, recreate kernel state */
174	continue;
175	}
176	}
177
178	fd_event (EV_A_ fd, got);
179	}
180
181	/* if the receive array was full, increase its size */
182	if (expect_false (eventcnt == epoll_eventmax))
183	{
184	ev_free (epoll_events);
185	epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1);
186	epoll_events = (struct epoll_event )ev_malloc (sizeof (struct epoll_event) epoll_eventmax);
187	}
188	}
189
190	int inline_size
191	epoll_init (EV_P_ int flags)
192	{
193	#ifdef EPOLL_CLOEXEC
194	backend_fd = epoll_create1 (EPOLL_CLOEXEC);
195
196	if (backend_fd <= 0)
197	#endif
198	backend_fd = epoll_create (256);
199
200	if (backend_fd < 0)
201	return 0;
202
203	fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
204
205	backend_fudge = 0.; /* kernel sources seem to indicate this to be zero */
206	backend_modify = epoll_modify;
207	backend_poll = epoll_poll;
208
209	epoll_eventmax = 64; /* initial number of events receivable per poll */
210	epoll_events = (struct epoll_event )ev_malloc (sizeof (struct epoll_event) epoll_eventmax);
211
212	return EVBACKEND_EPOLL;
213	}
214
215	void inline_size
216	epoll_destroy (EV_P)
217	{
218	ev_free (epoll_events);
219	}
220
221	void inline_size
222	epoll_fork (EV_P)
223	{
224	close (backend_fd);
225
226	while ((backend_fd = epoll_create (256)) < 0)
227	ev_syserr ("(libev) epoll_create");
228
229	fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
230
231	fd_rearm_all (EV_A);
232	}
233