.\"
.\"  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
.\"
.TH EPOLL 7 2007-06-22 "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
ꤷ椷ꤹ뤿ˡ
 3 ĤΥƥॳ뤬󶡤Ƥ:
.BR epoll_create (2),
.BR epoll_ctl (2),
.BR epoll_wait (2).

.B epoll

.BR epoll_create (2)
Ǻեǥץ³롣
եǥץФƻƤ
.BR epoll_ctl (2)
Ͽ롣
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
ǥХɲä롣
.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 (åȥꥬ) Ѥ륢ץꥱǤϡ
󥿥եϥ֥åʤ (non-blocking) եǥץ
Ȥ٤Ǥ롣
ϡ֥åɤ߹ߤ񤭹ߤˤäơ
ʣΥեǥץ򰷤
ߤƤޤΤ򤱤뤿Ǥ롣
.B epoll
򥨥åȥꥬ
.RB ( EPOLLET )
󥿥եȤƻȤƤˡϰʲ̤Ǥ롣
.RS
.TP
.B i
֥åʤեǥץȶ˻Ȥ
.TP
.B ii
.BR read (2)
ޤ
.BR write (2)

.B EAGAIN
֤ǤΤߡ٥ȤԤġ
.RE
.PP
٥ȥꥬ󥿥եȤƻȤϡ
.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 ʻ
٥ȥꥬ󥿥եȤƻѤȤ
.B epoll
λȤ
.BR poll (2)
ƱǤ롣
åȥꥬȤƻȤϡ
ץꥱΥ٥ȥ롼פǥȡ (stall) ʤ褦ˡ
ȤΤˤƤɬפ롣
Ǥϡꥹʤϥ֥åʤåȤǤꡢ
.BR listen (2)
ƤФƤ롣
ؿ do_use_fd() ϡ
.BR read (2)
ޤ
.BR write (2)
ˤä
.B EAGAIN
֤ޤǤϡѤߤΥեǥץȤ
٥ȶươȥޥ󥢥ץꥱϡ
.B EAGAIN
塢Ȥξ֤ϿƤ٤Ǥ롣
ˤꡢ do_use_fd() ƤӽФΤȤˡߤȤ
.BR read (2)
ޤ
.BR write (2)
³뤳ȤǤ롣

.nf
struct epoll_event ev, *events;

for (;;) {
    nfds = epoll_wait(kdpfd, events, maxevents, \-1);

    for (n = 0; n < nfds; ++n) {
        if (events[n].data.fd == listener) {
            client = accept(listener, (struct sockaddr *) &local,
                            &addrlen);
            if (client < 0){
                perror("accept");
                continue;
            }
            setnonblocking(client);
            ev.events = EPOLLIN | EPOLLET;
            ev.data.fd = client;
            if (epoll_ctl(kdpfd, EPOLL_CTL_ADD, client, &ev) < 0) {
                fprintf(stderr, "epoll set insertion error: fd=%d\\n",
                        client);
                return \-1;
            }
        } else {
            do_use_fd(events[n].data.fd);
        }
    }
}
.fi

åȥꥬ󥿥եȤƻȤ硢ǽͳˤꡢ

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

.B EPOLL_CTL_MOD
ꤷƸƤӽФȤ
.B EPOLLIN

.B EPOLLOUT
Ϣ³Ūڤؤ򤱤롣
.SS Ȳ
.TP
.B Q1
Ʊեǥץ 1 Ĥ epoll_set  2 ɲäȤɤʤ뤫
.TP
.B A1
֤
.B EEXIST

 2 ĤΥåɤƱեǥץ
2 ɲä뤳ȤϲǽǤ롣
̵ʾ֤Ǥ롣
.TP
.B Q2
2 Ĥ
.B epoll
åȤƱեǥץԤ뤳Ȥϲǽ
⤷ǽǤС٥Ȥξ
.B epoll
եǥץ𤵤뤫
.TP
.B A2
٥Ȥξ𤵤롣
侩ʤ
ޤ٥Ȥξ𤵤롣
.TP
.B Q3
.B epoll
եǥץȤ poll/epoll/select ǽ
.TP
.B A3
ǽǤ롣
.TP
.B Q4
.B epoll
եǥץ򼫿ȤΥեǥץåȤ
ɤʤ뤫
.TP
.B A4
Ԥ

.B epoll
եǥץ¾
.B epoll
եǥץåȤɲä뤳ȤϲǽǤ롣
.TP
.B Q5
.B epoll
եǥץ unix åȤ¾Υץ뤳Ȥϲǽ
.TP
.B A5
ԲǽǤ롣
.TP
.B Q6
եǥץ򥯥ȡΥեǥץƤ
.B epoll
åȤ鼫ưŪ˺뤫
.TP
.B A6
롣
.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
ɬפϤʤ
.BR epoll_wait (2)
饤٥Ȥ뤳Ȥϡ
֤Υեǥץ׵ᤵ줿 I/O ФƽѤߤǤ
ȤȤ桼˼ΤǤ롣
ּ
.B EAGAIN
ޤǤϥեǥץϽѤߤǤ
ñ˹ͤ٤Ǥ롣
Τ褦ʥեǥץ򤤤ĤɤΤ褦˻Ȥϡ
桼ǤƤ롣
ޤɤ߹ / 񤭹 I/O ֤ȤԤ줿֤ϡ
оݤȤʤեǥץɤ߹ǡ̤ޤ
񤭹ǡ̤å뤳ȤǸΤǤ롣
㤨С̤Υǡɤ߹ि
.BR read (2)
ƤȤˡ
.BR read (2)
֤Хȿ꾯ʤä硢
Υեǥץɤ߹ I/O ֤
ȤԤ줿Ȥʬ롣
.BR write (2)
Ȥäƽ񤭹ߤ򤹤Ȥ⡢ƱȤ롣
.SS ꤬ȤȲˡ
.TP
.B o  (starvation) (åȥꥬ)
.PP
礭 I/O ֤硢
 I/O ֤Υǡƽ (drain) 褦Ȥȡ
¾Υե뤬줺ȯ뤳Ȥ롣

.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
.SH 
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_ctl (2),
.BR epoll_wait (2)