libev/ev_epoll.c

/*
 * libev epoll fd activity backend
 *
 * Copyright (c) 2007,2008 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.
 *
 * 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.
 */

#include <sys/epoll.h>

void inline_size
unsigned_char_init (unsigned char *base, int count)
{
  /* memset might be overkill */
  while (count--)
    *base++ = 0;
}

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.
   * the fd is later added, 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 */
  ev.data.u64 = fd | ((uint64_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 ? 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 (backend_fd, epoll_events, epoll_eventmax, (int)ceil (timeout * 1000.));

  if (expect_false (eventcnt < 0))
    {
      if (errno != EINTR)
        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 got  = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
               | (ev->events & (EPOLLIN  | EPOLLERR | EPOLLHUP) ? EV_READ  : 0);
      int want = anfds [fd].events;

      if (anfds [fd].egen != (unsigned char)(ev->data.u64 >> 32))
        /*fprintf (stderr, "spurious notification fd %d, %d vs %d\n", fd, (int)(ev->data.u64 >> 32), anfds [fd].egen);*/
        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);

          epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev);
        }

      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)
{
  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; /* intiial 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)
    syserr ("(libev) epoll_create");

  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);

  fd_rearm_all (EV_A);
}

Revision:	1.36
Committed:	Mon Oct 27 11:08:29 2008 UTC (15 years, 6 months ago) by root
Content type:	text/plain
Branch:	MAIN
Changes since 1.35:	+16 -4 lines
Log Message:	work around epoll spurious notifications
#	User	Rev	Content
1	root	1.5	/*
2	root	1.9	* libev epoll fd activity backend
3			*
4	root	1.34	* Copyright (c) 2007,2008 Marc Alexander Lehmann <libev@schmorp.de>
5	root	1.5	* All rights reserved.
6			*
7	root	1.33	* 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	root	1.5	*
28	root	1.33	* 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	root	1.5	*/
39
40	root	1.32	/*
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			*
53			* lots of "weird code" and complication handling in this file is due
54			* to these design problems with epoll, as we try very hard to avoid
55			* epoll_ctl syscalls for common usage patterns.
56			*/
57
58	root	1.1	#include <sys/epoll.h>
59
60	root	1.35	void inline_size
61			unsigned_char_init (unsigned char *base, int count)
62			{
63			/* memset might be overkill */
64			while (count--)
65			*base++ = 0;
66			}
67
68	root	1.1	static void
69	root	1.13	epoll_modify (EV_P_ int fd, int oev, int nev)
70	root	1.1	{
71	root	1.32	struct epoll_event ev;
72	root	1.35	unsigned char oldmask;
73	root	1.32
74			/*
75			* we handle EPOLL_CTL_DEL by ignoring it here
76			* on the assumption that the fd is gone anyways
77			* if that is wrong, we have to handle the spurious
78			* event in epoll_poll.
79	root	1.35	* the fd is later added, we try to ADD it, and, if that
80			* fails, we assume it still has the same eventmask.
81	root	1.32	*/
82			if (!nev)
83			return;
84	root	1.1
85	root	1.35	oldmask = anfds [fd].emask;
86			anfds [fd].emask = nev;
87
88	root	1.36	/* store the generation counter in the upper 32 bits */
89			ev.data.u64 = fd \| ((uint64_t)++anfds [fd].egen << 32);
90	root	1.32	ev.events = (nev & EV_READ ? EPOLLIN : 0)
91			\| (nev & EV_WRITE ? EPOLLOUT : 0);
92
93			if (expect_true (!epoll_ctl (backend_fd, oev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))
94			return;
95
96			if (expect_true (errno == ENOENT))
97			{
98	root	1.35	/* if ENOENT then the fd went away, so try to do the right thing */
99	root	1.32	if (!nev)
100	root	1.36	goto dec_egen;
101	root	1.32
102			if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))
103			return;
104			}
105			else if (expect_true (errno == EEXIST))
106			{
107	root	1.35	/* 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	root	1.36	if (oldmask == nev)
110			goto dec_egen;
111
112			if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))
113	root	1.32	return;
114			}
115
116			fd_kill (EV_A_ fd);
117	root	1.36
118			dec_egen:
119			/* we didn't successfully call epoll_ctl, so decrement the generation counter again */
120			--anfds [fd].egen;
121	root	1.1	}
122
123	root	1.6	static void
124	root	1.13	epoll_poll (EV_P_ ev_tstamp timeout)
125	root	1.1	{
126	root	1.20	int i;
127	root	1.26	int eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, (int)ceil (timeout * 1000.));
128	root	1.1
129	root	1.29	if (expect_false (eventcnt < 0))
130	root	1.20	{
131			if (errno != EINTR)
132	root	1.21	syserr ("(libev) epoll_wait");
133	root	1.20
134			return;
135			}
136	root	1.1
137			for (i = 0; i < eventcnt; ++i)
138	root	1.32	{
139			struct epoll_event *ev = epoll_events + i;
140
141	root	1.36	int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */
142	root	1.32	int got = (ev->events & (EPOLLOUT \| EPOLLERR \| EPOLLHUP) ? EV_WRITE : 0)
143			\| (ev->events & (EPOLLIN \| EPOLLERR \| EPOLLHUP) ? EV_READ : 0);
144			int want = anfds [fd].events;
145
146	root	1.36	if (anfds [fd].egen != (unsigned char)(ev->data.u64 >> 32))
147			/fprintf (stderr, "spurious notification fd %d, %d vs %d\n", fd, (int)(ev->data.u64 >> 32), anfds [fd].egen);/
148			continue;
149
150	root	1.32	if (expect_false (got & ~want))
151			{
152	root	1.35	anfds [fd].emask = want;
153
154	root	1.32	/* we received an event but are not interested in it, try mod or del */
155	root	1.35	/* I don't think we ever need MOD, but let's handle it anyways */
156	root	1.32	ev->events = (want & EV_READ ? EPOLLIN : 0)
157			\| (want & EV_WRITE ? EPOLLOUT : 0);
158
159			epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev);
160			}
161
162			fd_event (EV_A_ fd, got);
163			}
164	root	1.1
165			/* if the receive array was full, increase its size */
166	root	1.14	if (expect_false (eventcnt == epoll_eventmax))
167	root	1.1	{
168	root	1.20	ev_free (epoll_events);
169	root	1.28	epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1);
170	root	1.23	epoll_events = (struct epoll_event )ev_malloc (sizeof (struct epoll_event) epoll_eventmax);
171	root	1.1	}
172			}
173
174	root	1.27	int inline_size
175	root	1.13	epoll_init (EV_P_ int flags)
176	root	1.1	{
177	root	1.26	backend_fd = epoll_create (256);
178	root	1.1
179	root	1.26	if (backend_fd < 0)
180	root	1.13	return 0;
181	root	1.3
182	root	1.26	fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
183	root	1.1
184	root	1.31	backend_fudge = 0.; /* kernel sources seem to indicate this to be zero */
185	root	1.25	backend_modify = epoll_modify;
186			backend_poll = epoll_poll;
187	root	1.1
188	root	1.14	epoll_eventmax = 64; /* intiial number of events receivable per poll */
189	root	1.23	epoll_events = (struct epoll_event )ev_malloc (sizeof (struct epoll_event) epoll_eventmax);
190	root	1.13
191	root	1.24	return EVBACKEND_EPOLL;
192	root	1.1	}
193	root	1.6
194	root	1.27	void inline_size
195	root	1.15	epoll_destroy (EV_P)
196			{
197	root	1.20	ev_free (epoll_events);
198	root	1.15	}
199
200	root	1.27	void inline_size
201	root	1.15	epoll_fork (EV_P)
202			{
203	root	1.26	close (backend_fd);
204	root	1.21
205	root	1.26	while ((backend_fd = epoll_create (256)) < 0)
206	root	1.22	syserr ("(libev) epoll_create");
207	root	1.21
208	root	1.26	fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
209	root	1.15
210	root	1.16	fd_rearm_all (EV_A);
211	root	1.15	}
212