.\" Copyright (C) 2008 Michael Kerrisk <mtk.manpages@gmail.com>
.\" starting from a version by Davide Libenzi <davidel@xmailserver.org>
.\"
.\" 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
.\"
.\" 2008-10-10, mtk: describe eventfd2(), and EFD_NONBLOCK and EFD_CLOEXEC
.\"
.\" Japanese Version Copyright (c) 2008  Akihiro MOTOKI
.\"         all rights reserved.
.\" Translated 2008-04-08, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2008-11-10, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v3.13
.\" 
.TH EVENTFD 2 2009-01-26 Linux "Linux Programmer's Manual"
.SH ̾
eventfd \- ٥ѤΥեǥץ
.SH 
.B #include <sys/eventfd.h>
.sp
.BI "int eventfd(unsigned int " initval ", int " flags );
.SH 
.BR eventfd ()
 "eventfd ֥" 롣
eventfd ֥Ȥϥ桼֥ץꥱ󤬥٥Ԥ/Ѥ
ȤߤȤƻȤȤǤ롣ޤͥ뤬桼֥ץꥱ
٥ȤΤ뤿ˤȤȤǤ롣
Υ֥Ȥˤϡunsigned  64 ӥå
.RI ( uint64_t )
Υ󥿤ޤޤƤꡢΥ󥿤ϥͥˤ롣
Υ󥿤
.I initval
ǻꤵ줿ͤǽ롣

Linux 2.6.27 ʹߤǤϡ
ʲͤΤĤӥåñ̤ (OR) ǻꤹ뤳Ȥǡ
.BR eventfd ()
ο񤤤ѹ뤳ȤǤ롣
.TP 14
.B EFD_NONBLOCK
륪ץե뵭 (open file description) 
.B O_NONBLOCK
ե륹ơե饰򥻥åȤ롣
Υե饰ȤȤǡ
.B O_NONBLOCK
򥻥åȤ뤿
.BR fcntl (2)
ɲäǸƤӽФɬפʤʤ롣
.TP
.B EFD_CLOEXEC
եǥץФ
close-on-exec
.RB ( FD_CLOEXEC )
ե饰򥻥åȤ롣
Υե饰ΩͳˤĤƤϡ
.BR open (2)

.B O_CLOEXEC
ե饰򻲾ȤΤȡ
.PP
С 2.6.26  Linux Ǥϡ
.I flags
̤ѤǤꡢ0 ꤷʤФʤʤ

.BR eventfd ()
 eventfd ֥Ȥ򻲾ȤΤ˻ѤǤ뿷եǥץ
֤֤줿եǥץФƤϰʲ¹ԤǤ롣
.TP
.BR read (2)
eventfd 󥿤 0 ʳͤξ硢
.BR read (2)
ϥͤǼ 8 ХȤ֤ͤ
ͤ 0 ˥ꥻåȤ
(֤ͤϥۥȡХȥĤޤ
ۥȥޥɽѤХȥdzǼ)
.IP
.BR read (2)
λǥ󥿤 0 ξ硢
.BR read (2)
ϥ󥿤 0 ʳˤʤޤ (block) 롢
⤷ϥեǥץ (non-blocking)
ꤵƤϥ顼
.B EAGAIN
ǼԤ롣
.IP
Ϥ줿Хåե礭 8 Х̤ξ硢
.BR read (2)
ϥ顼
.B EINVAL
ǼԤ롣
.TP
.BR write (2)
.BR write (2)
ϡΥХåեϤ줿 8 ХȤͤ򥫥󥿤˲û롣
󥿤˳Ǽǽʺͤ unsigned  64 ӥåκͤ
1  (ʤ 0xfffffffffffffffe) Ǥ롣
ûԤȥͤͤĶ᤹ˤϡ
ΥեǥץФ
.BR read (2)
¹Ԥޤǡ
.BR write (2)
 (block) 롢
⤷ϥեǥץ (non-blocking)
ꤵƤϥ顼
.B EAGAIN
ǼԤ롣
.IP
Ϥ줿Хåե礭 8 Х̤ξ硢⤷
 0xffffffffffffffff 񤭹⤦Ȥ硢
.BR write (2)
ϥ顼
.B EINVAL
ǼԤ롣
.TP
.BR poll "(2), " select "(2) (Ʊͤ)"
֤줿եǥץϡ
.BR poll (2)
.RB ( epoll (7)
Ʊ) 
.BR select (2)
򥵥ݡȤƤꡢʲΤ褦ư򤹤롣
.RS
.IP * 3
󥿤 0 礭ͤξ硢
եǥץɤ߽ФǽȤʤ
.RB ( select (2)

.I readfds

.BR poll (2)

.B POLLIN
ե饰)
.IP *
ʤȤ "1"  (block) ȼ鷺˽񤭹硢
եǥץϽ񤭹߲ǽȤʤ
.RB ( select (2)

.I writefds

.BR poll (2)

.B POLLOUT
ե饰)
.IP *
ͤΥСեФ줿硢
.BR select (2)
ϥեǥץɤ߽ФǽȽ񤭹߲ǽξΤ
.BR poll (2)

.B POLLERR
٥Ȥ֤
Ҥ̤ꡢ
.BR write (2)
ǥ󥿤Сե뤳ȤϷ褷Ƥʤ
ʤ顢 KAIO ֥ƥˤä 2^64  eventfd "signal posts" 
¹Ԥ줿ˤϥСե
(ŪˤϤ뤬ŪˤϤʤ)
Сեȯ硢
.BR read (2)

.I uint64_t
κ (ʤ 0xffffffffffffffff) ֤
.RE
.IP
eventfd եǥץϡʳΥեǥץ
¿ API Ǥ
.BR pselect (2),
.BR ppoll (2),
.BR epoll (7)
⥵ݡȤƤ롣
.TP
.BR close (2)
եǥץʹߤɬפʤʤäݤˤϡ٤Ǥ롣
Ʊ eventfd ֥Ȥ˴Ϣդ줿եǥץ
ȡΥ֥Ѥλ񸻤ͥˤ롣
.PP
.BR fork (2)
줿ҥץϡ
.BR eventfd ()
줿եǥץΥԡѾ롣
ʣ줿եǥץƱ eventfd ֥Ȥ˴Ϣդ롣
.BR execve (2)

.BR eventfd ()
줿եǥץݻ롣
.SH ֤
ȡ
.BR eventfd ()
Ͽ eventfd եǥץ֤
顼ξ硢\-1 ֤
.I errno
˥顼򼨤ͤꤹ롣
.SH 顼
.TP
.B EINVAL
.I flags
̵
Linux 2.6.26 Ǥϡ
.I flags
 0 ʳ͡
.TP
.B EMFILE
ץѤߤΥեǥץοץξ¤
ãƤ
.TP
.B ENFILE
ץѤߤΥեƥΤξ¤ãƤ
.TP
.B ENODEV
.\" Note from Davide:
.\" The ENODEV error is basically never going to happen if
.\" the kernel boots correctly. That error happen only if during
.\" the kernel initialization, some error occur in the anonymous
.\" inode source initialization.
(ͥ) ̵̾ inode ǥХޥȤǤʤä
.TP
.B ENOMEM
 eventfd եǥץΤ˽ʬʥ꤬ʤä
.SH С
.BR eventfd ()
ϥͥ 2.6.22 ʹߤ Linux ѲǽǤ롣
ư glibc ¦ΥݡȤϥС 2.8 ʹߤ󶡤Ƥ롣
.\" eventfd() is in glibc 2.7, but reportedly does not build
.BR eventfd2 ()
ƥॳ (ա׻) 
ͥ 2.6.27 ʹߤ Linux ѲǽǤ롣
С 2.9 ʹߤǤϡglibc 
.BR eventfd ()
Υåѡؿϡͥ뤬бƤ
.BR eventfd2 ()
ƥॳѤ롣
.SH 
.BR eventfd ()

.BR eventfd2 ()
 Linux ͭǤ롣
.SH 
ץꥱϡѥפ򥤥٥ȤΤ뤿˻ѤƤ
Ƥξ̤ˤơѥפ eventfd եǥץ
Ѥ뤳ȤǤ롣
eventfd եǥץȤѥפȤ٤
ͥǤΥХإåɤ٤ȤäȾեǥץ
ĤɬפȤʤ (ѥפξɬפǤ)

ͥǻѤȡeventfd եǥץ
֤ͥȥ桼֤Υ֥åǽ󶡤뤳ȤǤ
㤨 KAIO (kernel AIO)
.\"  eventually syslets/threadlets
Τ褦ʵǽեǥץ˲餫λȤ
Τ뤳ȤǤ롣

eventfd եǥץνפϡ
eventfd եǥץ
.BR select (2),
.BR poll (2),
.BR epoll (7)
Ȥä¾ΥեǥץƱͤ˴ƻǤǤ롣
ΤȤϡץꥱϡֽ (traditional) եξѲ
eventfd 󥿥ե򥵥ݡȤ¾Υͥ뵡ξѲƱ˴ƻ
Ǥ뤳Ȥ̣
.RB ( eventfd ()
󥿥եʤˤϡΥͥ뵡
.BR select (2),
.BR poll (2),
.BR epoll (7)
ͳ¿Ť뤳ȤϤǤʤä)
.SS ؤˤ Linux Υƥॳ
ؤˤ Linux ƥॳढꡢ
.BR eventfd ()
ȡäȿ
.BR eventfd2 ()
Ǥ롣
.BR eventfd ()

.I flags
Ƥʤ
.BR eventfd2 ()
ǤϾ嵭ͤ
.I flags
Ƥ롣
glibc Υåѡؿϡ
.BR eventfd2 ()
ѲǽǤСѤ롣
.SS glibc ɲõǽ
GNU C 饤֥ϡeventfd եǥץɤ߽ФȽ񤭹ߤ
ؤܺ٤ΤĤݲ뤿ˡĤηȡĤδؿɲä
Ƥ롣
.in +4n
.nf

typedef uint64_t eventfd_t;

int eventfd_read(int fd, eventfd_t *value);
int eventfd_write(int fd, eventfd_t value);
.fi
.in

δؿϡeventfd եǥץФɤ߽Ф
񤭹ߤ¹ԤХȿž줿ˤ
0 ֤Ǥʤ \-1 ֤
.SH 
.PP
ʲΥץ eventfd եǥץ
θ fork ¹Ԥƻҥץ롣
ƥץδ sleep ֤ˡҥץ
ץΥޥɥ饤ǻꤵ줿()򤽤줾
eventfd եǥץ˽񤭹ࡣ
ƥץ sleep λ eventfd եǥץ
ɤ߽ФԤ

ʲ˼륻åˤΥץλȤ򼨤
.in +4n
.nf

.RB "$" " ./a.out 1 2 4 7 14"
Child writing 1 to efd
Child writing 2 to efd
Child writing 4 to efd
Child writing 7 to efd
Child writing 14 to efd
Child completed write loop
Parent about to read
Parent read 28 (0x1c) from efd
.fi
.in
.SS ץΥ
\&
.nf
#include <sys/eventfd.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>             /* Definition of uint64_t */

#define handle_error(msg) \\
    do { perror(msg); exit(EXIT_FAILURE); } while (0)

int
main(int argc, char *argv[])
{
    int efd, j;
    uint64_t u;
    ssize_t s;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s <num>...\\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    efd = eventfd(0, 0);
    if (efd == \-1)
        handle_error("eventfd");

    switch (fork()) {
    case 0:
        for (j = 1; j < argc; j++) {
            printf("Child writing %s to efd\\n", argv[j]);
            u = strtoull(argv[j], NULL, 0);
                    /* strtoull() allows various bases */
            s = write(efd, &u, sizeof(uint64_t));
            if (s != sizeof(uint64_t))
                handle_error("write");
        }
        printf("Child completed write loop\\n");

        exit(EXIT_SUCCESS);

    default:
        sleep(2);

        printf("Parent about to read\\n");
        s = read(efd, &u, sizeof(uint64_t));
        if (s != sizeof(uint64_t))
            handle_error("read");
        printf("Parent read %llu (0x%llx) from efd\\n",
                (unsigned long long) u, (unsigned long long) u);
        exit(EXIT_SUCCESS);

    case \-1:
        handle_error("fork");
    }
}
.fi
.SH Ϣ
.BR futex (2),
.BR pipe (2),
.BR poll (2),
.BR read (2),
.BR select (2),
.BR signalfd (2),
.BR timerfd_create (2),
.BR write (2),
.BR epoll (7),
.BR sem_overview (7)