.\"
.\"  epoll by Davide Libenzi ( efficient event notification retrieval )
.\"  Copyright (C) 2003  Davide Libenzi
.\"
.\"  This program is free software; you can redistribute it and/or modify
.\"  it under the terms of the GNU General Public License as published by
.\"  the Free Software Foundation; either version 2 of the License, or
.\"  (at your option) any later version.
.\"
.\"  This program is distributed in the hope that it will be useful,
.\"  but WITHOUT ANY WARRANTY; without even the implied warranty of
.\"  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\"  GNU General Public License for more details.
.\"
.\"  You should have received a copy of the GNU General Public License
.\"  along with this program; if not, write to the Free Software
.\"  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
.\"
.\"  Davide Libenzi <davidel@xmailserver.org>
.\"
.\" Japanese Version Copyright (c) 2004-2005 Yuichi SATO
.\"         all rights reserved.
.\" Translated Sat Jun 19 07:50:04 JST 2004
.\"         by Yuichi SATO <ysato444@yahoo.co.jp>
.\" Updated & Modified 2005-01-18, Yuichi SATO
.\" Updated 2006-07-14, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\"         Catch up to LDP v2.34. epoll.4 is renamed to epoll.7.
.\" Updated 2007-09-07, Akihiro MOTOKI, LDP v2.64
.\" Updated 2008-04-08, Akihiro MOTOKI, LDP v2.79
.\" Updated 2009-02-23, Akihiro MOTOKI, LDP v3.19
.\"
.TH EPOLL 7 2009-02-01 "Linux" "Linux Programmer's Manual"
.SH ̾
epoll \- I/O ٥εǽ
.SH 
.B #include <sys/epoll.h>
.SH 
.B epoll

.BR poll (2)
ΰǤꡢåȥꥬ󥿥ե
٥ȥꥬ󥿥եΤɤȤƤѤ뤳ȤǤ
ƻ뤹եǥץο¿ˤѤǤ롣
.B epoll
󥹥󥹤κԤ
ʲΥƥॳ뤬󶡤Ƥ:
.IP * 3
.B epoll
󥹥󥹤
.BR epoll_create (2)
Ǻ롣
.BR epoll_create (2)
Ϻ epoll 󥹥󥹤򻲾Ȥեǥץ֤
(äȿ
.BR epoll_create1 (2)
Ǥϡ
.BR epoll_create (2)
εǽĥƤ)
.IP *
ΥեǥץФƻƤ
.BR epoll_ctl (2)
Ͽ롣
.B epoll
󥹥󥹤˸ϿƤեǥץν
.I epoll
ȸƤФ뤳Ȥ⤢롣
.IP *
Ǹ
.BR epoll_wait (2)
ǼºݤΥ٥Ԥ򳫻Ϥ롣
.SS ٥ȥꥬȥåȥꥬ
.B epoll
٥ (distribution) 󥿥եϡ
åȥꥬ (ET) ȤƤ٥ȥꥬ (LT) ȤƤư뤳ȤǤ롣
Ĥΰ㤤ϡΤ褦Ǥ롣
Τ褦ʥʥꥪäȤ褦:
.IP 1. 3
ѥפɤ߹¦ɽեǥץ
.RI ( rfd )

.B epoll
󥹥󥹤Ͽ롣
.IP 2.
ѥפؽ񤭹ץब 2 kB Υǡѥפν񤭹¦ؽ񤭹ࡣ
.IP 3.
.BR epoll_wait (2)
ƤӽФȡɤ߹߲ǽ (ready) ʥեǥץȤ
.I rfd
֤롣
.IP 4.
ѥפɤ߽Фץब1 kB Υǡ
.I rfd
ɤ߽Ф
.IP 5.
.BR epoll_wait (2)
θƤӽФԤ롣
.PP
.I rfd
եǥץ
.B EPOLLET
ե饰 (åȥꥬ) Ȥä
.B epoll
ɲäƤȡ
ѲǽʥǡեϥХåեˤޤ¸ߤˤ⤫餺
ƥå
.B 5

.BR epoll_wait (2)
θƤӽФǥϥ󥰤ǽ롣
ΰǡ⡼Ȥ³ (peer) ϴ줿ǡ
ŤƱԤƤ뤫⤷ʤ
Τ褦ʤȤͳϡåȥꥬ٥Ǥϡ
˥Ƥեǥ٥ȤäȤˤΤߥ٥Ȥ
뤿Ǥ롣
äơƥå
.B 5
ǤϡƤӽФ¦ϷŪ
ϥХåեˤ¸ߤǡԤĤȤˤʤ뤫⤷ʤ
嵭Ǥϡ
.B 2
ǹԤ줿񤭹ߤˤä
.I rfd
˴ؤ륤٥Ȥ졢
.B 3
ǥ٥Ȥ (consume) 롣
.B 4
ǹԤɤ߹ǤϡΥХåեǡ񤷤ʤΤǡ
ƥå
.B 5
ǹԤ
.BR epoll_wait (2)
θƤӽФ
̵¤ (block) 뤫⤷ʤ

.B EPOLLET
ե饰Ѥ륢ץꥱǤϡ
󥿥եϥ֥åʤ (non-blocking) եǥץ
Ȥ٤Ǥ롣
ϡ֥åɤ߹ߤ񤭹ߤˤäơ
ʣΥեǥץ򰷤
ߤƤޤΤ򤱤뤿Ǥ롣
.B epoll
򥨥åȥꥬ
.RB ( EPOLLET )
󥿥եȤƻȤƤˡϰʲ̤Ǥ롣
.RS
.TP 4
.B i
֥åʤեǥץȶ˻Ȥ
.TP
.B ii
.BR read (2)
ޤ
.BR write (2)

.B EAGAIN
֤ǤΤߡ٥ȤԤġ
.RE
.PP
٥ȥꥬ󥿥եȤƻȤ
 (餬ǥեȤǤ롢
.B EPOLLET
ꤵʤä)
.B epoll
ñ˹®
.BR poll (2)
ǤꡢȤƱʤΤǡ
.BR poll (2)
ȤƤȤǤϤɤǤѤ뤳ȤǤ롣

åȥꥬȤäǤ⡢ʣΥǡʣ
.B epoll
٥ȤΤǡ
ƤӽФ¦ˤ
.B EPOLLONESHOT
ե饰ꤹ륪ץ󤬤롣
Υե饰
.B epoll
Фơ
.BR epoll_wait (2)
ˤ륤٥ȤǡϢեǥץ̵ˤ롣
.B EPOLLONESHOT
ե饰ꤵ줿硢
.BR epoll_ctl (2)

.B EPOLL_CTL_MOD
ꤷƥեǥץٻѤǤ褦ˤΤϡ
ƤӽФ¦ǤǤ롣
.SS /proc 󥿥ե
epoll 񤹤륫̤ͥ¤뤿ˡ
ʲΥ󥿥եѤ뤳ȤǤ롣
.TP
.\" Following was added in 2.6.28, but them removed in 2.6.29
.\" .TP
.\" .IR /proc/sys/fs/epoll/max_user_instances " (since Linux 2.6.28)"
.\" This specifies an upper limit on the number of epoll instances
.\" that can be created per real user ID.
.TP
.IR /proc/sys/fs/epoll/max_user_watches " (Linux 2.6.28 ʹ)"
Υեϡ桼ƥƤ epoll 󥹥󥹤
ϿǤեǥץξ¤ꤹ롣
ξ¤ϼ¥桼 ID ñ̤Ǥ롣
Ͽ줿եǥץ 1 Ĥ񤹤̤ϡ
32 ӥåȥͥǤ褽 90 Хȡ
64 ӥåȥͥǤ褽 160 ХȤǤ롣
.\" 2.6.29 (in 2.6.28, the default was 1/32 of lowmem)
ߤΤȤ
.I max_user_watches
ΥǥեͤϡѲǽʥ겼¤ 1/25 (4%) Ǥꡢ
ϿǾ񤵤 (Хñ) dzäͤȤʤ롣
.SS ʻ
٥ȥꥬ󥿥եȤƻѤȤ
.B epoll
λȤ
.BR poll (2)
ƱǤ롣
åȥꥬȤƻȤϡ
ץꥱΥ٥ȥ롼פǥȡ (stall) ʤ褦ˡ
ȤΤˤƤɬפ롣
Ǥϡꥹʤϥ֥åʤåȤǤꡢ
.BR listen (2)
ƤФƤ롣
ؿ
.I do_use_fd()
ϡ
.BR read (2)
ޤ
.BR write (2)
ˤä
.B EAGAIN
֤ޤǤϡѤߤΥեǥץȤ
٥ȶươȥޥ󥢥ץꥱϡ
.B EAGAIN
塢Ȥξ֤ϿƤ٤Ǥ롣
ˤꡢ
.I do_use_fd()
ƤӽФΤȤˡߤȤ
.BR read (2)
ޤ
.BR write (2)
³뤳ȤǤ롣

.in +4n
.nf
#define MAX_EVENTS 10
struct epoll_event ev, events[MAX_EVENTS];
int listen_sock, conn_sock, nfds, epollfd;

/* Set up listening socket, \(aqlisten_sock\(aq (socket(),
   bind(), listen()) */

epollfd = epoll_create(10);
if (epollfd == \-1) {
    perror("epoll_create");
    exit(EXIT_FAILURE);
}

ev.events = EPOLLIN;
ev.data.fd = listen_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == \-1) {
    perror("epoll_ctl: listen_sock");
    exit(EXIT_FAILURE);
}

for (;;) {
    nfds = epoll_wait(epollfd, events, MAX_EVENTS, \-1);
    if (nfds == \-1) {
        perror("epoll_pwait");
        exit(EXIT_FAILURE);
    }

    for (n = 0; n < nfds; ++n) {
        if (events[n].data.fd == listen_sock) {
            conn_sock = accept(listen_sock,
                            (struct sockaddr *) &local, &addrlen);
            if (conn_sock == \-1) {
                perror("accept");
                exit(EXIT_FAILURE);
            }
            setnonblocking(conn_sock);
            ev.events = EPOLLIN | EPOLLET;
            ev.data.fd = conn_sock;
            if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock,
                        &ev) == \-1) {
                perror("epoll_ctl: conn_sock");
                exit(EXIT_FAILURE);
            }
        } else {
            do_use_fd(events[n].data.fd);
        }
    }
}
.fi
.in

åȥꥬ󥿥եȤƻȤ硢ǽͳˤꡢ

.RB ( EPOLLIN | EPOLLOUT )
ꤷƤ
.RB ( EPOLL_CTL_ADD
) եǥץ
.B epoll
󥿥եɲä뤳ȤǤ롣
ˤꡢ
.BR epoll_ctl (2)

.B EPOLL_CTL_MOD
ꤷƸƤӽФȤ
.B EPOLLIN

.B EPOLLOUT
Ϣ³Ūڤؤ򤱤롣
.SS Ȳ
.TP 4
.B Q0
.B epoll
Ͽ줿եǥץ̤ˤϡ
򥭡ȤƻȤФ褤
.TP
.B A0
ϥեǥץֹȥץե뵭 (open file
description) ȤǤ (ץե뵭Ҥ "open file handle" Ȥ
ƤФ졢ץ󤵤줿եΥͥɽǤ)
.TP
.B Q1
1 Ĥ
.B epoll
󥹥󥹤Ʊեǥץ 2 ϿȤɤʤ뤫
.TP
.B A1
֤
.B EEXIST

ʤ顢Ʊ
.B epoll
󥹥󥹤Фʣ줿ǥץɲä뤳ȤϲǽǤ
.RB ( dup (2),
.BR dup2 (2),
.BR fcntl (2)
.B F_DUPFD
ʤ)
.\" But a descriptor duplicated by fork(2) can't be added to the
.\" set, because the [file *, fd] pair is already in the epoll set.
.\" That is a somewhat ugly inconsistency.  On the one hand, a child process
.\" cannot add the duplicate file descriptor to the epoll set.  (In every
.\" other case that I can think of, descriptors duplicated by fork have
.\" similar semantics to descriptors duplicated by dup() and friends.)  On
.\" the other hand, the very fact that the child has a duplicate of the
.\" descriptor means that even if the parent closes its descriptor, then
.\" epoll_wait() in the parent will continue to receive notifications for
.\" that descriptor because of the duplicated descriptor in the child.
.\"
.\" See http://thread.gmane.org/gmane.linux.kernel/596462/
.\" "epoll design problems with common fork/exec patterns"
.\"
.\" mtk, Feb 2008
ʣեǥץۤʤ
.I events
ޥϿС٥Ȥե륿󥰤Τ
εǽͭѤʼˡǤ롣
.TP
.B Q2
2 Ĥ
.B epoll
󥹥󥹤ƱեǥץԤ뤳Ȥϲǽ
⤷ǽǤС٥Ȥξ
.B epoll
եǥץ𤵤뤫
.TP
.B A2
٥Ȥξ𤵤롣
ʤ顢ˤտץߥ󥰤ɬפ
뤫⤷ʤ
.TP
.B Q3
.B epoll
եǥץȤ poll/epoll/select ǽ
.TP
.B A3
ǽǤ롣
.B epoll
եǥץ˽ԤΥ٥Ȥϡ
ɤ߽ФǽΤ뤳Ȥ
.TP
.B Q4
.B epoll
եǥץ򼫿ȤΥեǥץ
褦ȤȤɤʤ뤫
.TP
.B A4
.BR epoll_ctl (2)
θƤӽФ
.RB ( EINVAL
) Ԥ

.B epoll
եǥץ¾
.B epoll
եǥץɲä뤳ȤϲǽǤ롣
.TP
.B Q5
.B epoll
եǥץ Unix ɥᥤ󥽥åȤ¾Υץ뤳Ȥϲǽ
.TP
.B A5
ǽ򤹤뤳Ȥ˰̣Ϥʤ
ʤʤ顢¦Υץ
.B epoll
ΥեǥץΥԡäƤʤǤ롣
.TP
.B Q6
եǥץ򥯥ȡΥեǥץƤ
.B epoll
礫鼫ưŪ˺뤫
.TP
.B A6
뤬ʲդɬפǤ롣
եǥץϥץե뵭
.RB ( open (2)
) ؤλȤǤ롣
ǥץʣ
.BR dup (2),
.BR dup2 (2),
.BR fcntl (2)

.B F_DUPFD

.BR fork (2)
ͳǹԤ٤ˡƱץե뵭Ҥ򻲾Ȥ뿷Υե
ǥץ롣
ץե뵭ҼΤϡȤ򻲾ȤƤΥեǥץ
ޤ¸ߤ³롣
եǥץ
.B epoll
礫Τϡб륪ץե뵭Ҥ򻲾ȤƤ
ƤΥեǥץ줿Ǥ
.RB ( epoll_ctl ()
.B EPOLL_CTL_DEL
ȤäƤΥǥץŪ˺ˤ)
ΤȤϡ
.B epoll
°Ƥ뤢եǥץ򥯥ǤäƤ⡢
Ʊե뵭Ҥ򻲾Ȥ¾Υեǥץץ󤵤Ƥ֤ϡ
եǥץ˥٥Ȥ𤵤ǽ
Ȥ̣롣
.TP
.B Q7
2 İʾΥ٥Ȥ
.BR epoll_wait (2)
δ֤ȯ硢ϤޤȤ𤵤뤫
Ȥ̡𤵤뤫
.TP
.B A7
ޤȤ𤵤
.TP
.B Q8
եǥץФϡ
˽Ƥ뤬ޤ𤵤Ƥʤ٥Ȥ˱ƶ뤫
.TP
.B A8
¸ΥեǥץФ 2 ĤԤȤǤ롣
ξ硢ˤϰ̣ʤ
ѹȡѲǽ I/O Ƥɤ߹ޤ롣
.TP
.B Q9
.B EPOLLET
ե饰 (åȥꥬư) ȤäƤ硢
.B EAGAIN
ޤǡ
³ƥեǥץɤ߽񤭤ɬפ뤫
.TP
.B A9
.BR epoll_wait (2)
饤٥Ȥ뤳Ȥϡ
Υեǥץ׵ᤵ줿 I/O ФƽѤߤǤ롢
ȤȤ桼˼ΤǤ롣
 (֥åʤ) read/write 
.B EAGAIN
ޤǤϥեǥץϽѤߤǤ
ͤʤФʤʤ
Υեǥץ򤤤ĤɤΤ褦˻Ȥϡ
桼ǤƤ롣
.sp
ѥåȻظȡظΥե (㤨Сǡॽåȡ
canonical ⡼ɤü) Ǥϡ
ɤ߹ / 񤭹Ѥ I/O ֤Τͣˡ
.B EAGAIN
ˤʤޤ read/write ԤȤǤ롣
.sp
ȥ꡼ظΥե (㤨СѥסFIFOȥ꡼ॽå) Ǥϡ
ɤ߹ / 񤭹Ѥ I/O ֤ȤԤ줿֤ϡ
оݤȤʤեǥץɤ߹ǡ̤ޤ
񤭹ǡ̤å뤳ȤǤ⸡ΤǤ롣
㤨С̤Υǡɤ߹ि
.BR read (2)
ƤȤˡ
.BR read (2)
֤Хȿ꾯ʤä硢
Υեǥץɤ߹ I/O ֤
ȤԤ줿Ȥʬ롣
.BR write (2)
Ȥäƽ񤭹ߤ򤹤Ȥ⡢ƱȤ
(ƻ뤷Ƥեǥץ˥ȥ꡼ظΥե
ȤƤ뤳ȤݾڤǤʤˤϡԤμˡλѤ򤱤뤳)
.SS ꤬ȤȲˡ
.TP
.B o  (starvation) (åȥꥬ)
.PP
礭 I/O ֤硢
 I/O ֤Υǡƽ (drain) 褦Ȥȡ
¾Υե뤬줺ȯ뤳Ȥ
(
.B epoll
˸ͭΤΤǤϤʤ)
.PP
βˡϡѤ߾֤ΥꥹȤơ
Ϣ data ¤Τǥեǥץ
ѲǽǤȥޡ뤳ȤǤ롣
ˤäơѲǽʤ٤ƤΥե
ɤΥեɬפ뤫򲱤뤳ȤǤ
֤˽ (round robin) 뤳ȤǤ롣
ѲǽǤեǥץФ
ʸ˼륤٥Ȥ̵뤹뤳ȤǤ롣
.TP
.B o ٥ȥåȤäƤ
.PP
٥ȥåȤäƤ硢
ޤ
.BR epoll_wait (2)
֤줿ƤΥեǥץǼƤ硢
줿ȤưŪ˥ޡ
(ĤޤΥ٥Ȥνˤäƥޡ) ˡ󶡤٤Ǥ롣
.BR epoll_wait (2)
 100 ĤΥ٥Ȥꡢ
٥ #47 ǤϤǥ٥ #13 ĤȲꤹ롣
٥ #13 ι¤Τեǥץ
.BR close (2)
ȡ٥ȥåϤΥեǥץԤĥ٥Ȥ
¸ߤȤäơ𤬵롣
.PP
褹 1 Ĥˡϡ٥ 47 ν򤷤Ƥ֤ˡ
եǥץ 13 
.BR close (2)
뤿
.BR epoll_ctl ( EPOLL_CTL_DEL )
ƤӽФϢդ줿 data ¤ΤѤߤȥޡơ
꡼󥢥åץꥹȤ˥󥯤뤳ȤǤ롣
Хåǥեǥץ 13 ˤĤƤ
¾Υ٥Ȥ򸫤Ĥ硢
Υեǥץ˺줿ΤǤʬΤǡ
ϵʤ
.SH С
.B epoll
API  Linux ͥ 2.5.44 Ƴ줿
.\" 󥿥ե Linux ͥ 2.5.66 dzꤵ٤Ǥ롣
glibc ǤΥݡȤϥС 2.3.2 ɲä줿
.SH 
.B epoll
API  Linux ͭǤ롣
¾ΥƥǤƱͤε󶡤Ƥ礬롣
㤨СFreeBSD 
.I kqueue
 Solaris 
.I /dev/poll
ʤɤǤ롣
.SH Ϣ
.BR epoll_create (2),
.BR epoll_create1 (2),
.BR epoll_ctl (2),
.BR epoll_wait (2)