.\" This manpage is copyright (C) 2001 Paul Sheer.
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" very minor changes, aeb
.\"
.\" Modified 5 June 2002, Michael Kerrisk <mtk.manpages@gmail.com>
.\" 2006-05-13, mtk, removed much material that is redundant with select.2
.\"             various other changes
.\"
.\" Translated 2002-02-21, NAKANO Takeo <nakano@apm.seikei.ac.jp>
.\" Updated 2002-09-23, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2005-03-15, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2006-07-21, Akihiro MOTOKI, LDP v2.36
.\"
.\"WORD: file descriptor	եǥץ
.\"
.TH SELECT_TUT 2 2007-12-18 "Linux" "Linux Programmer's Manual"
.SH ̾
select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO \- Ʊ I/O ¿Ų
.SH 
.nf
/* POSIX.1-2001 ˽ */
.br
.B #include <sys/select.h>
.sp
/* εʤ˽ */
.br
.B #include <sys/time.h>
.br
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.sp
.BI "int select(int " nfds ", fd_set *" readfds ", fd_set *" writefds ,
.BI "           fd_set *" exceptfds ", struct timeval *" utimeout );
.sp
.BI "void FD_CLR(int " fd ", fd_set *" set );
.br
.BI "int  FD_ISSET(int " fd ", fd_set *" set );
.br
.BI "void FD_SET(int " fd ", fd_set *" set );
.br
.BI "void FD_ZERO(fd_set *" set );
.sp
.B #include <sys/select.h>
.sp
.BI "int pselect(int " nfds ", fd_set *" readfds ", fd_set *" writefds ,
.BI "            fd_set *" exceptfds ", const struct timespec *" ntimeout ,
.BI "            const sigset_t *" sigmask );
.fi
.sp
.in -4n
glibc εǽޥ׷
.RB ( feature_test_macros (7)
):
.in
.sp
.BR pselect ():
_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
.SH 
.BR select ()
(
.BR pselect ())
ϡƱʣΥեǥץ (䥽åȥϥɥ)
ΨŪ˰Ȥ C ץǡפȤʤؿǤ롣
δؿμפʰϡ3Υեǥץ
\fIreadfds\fP, \fIwritefds\fP, \fIexceptfds\fP Ǥ롣
.BR select ()
̾λȤϡҤȤĤޤʣΥեǥץ
־֤ѲפԤäƤ֡ (block) 뤳ȤǤ롣
־֤ѲפȤϡʲΤ줫ξǤ:
(1) եǥץǤʸ硢
(2) եǥץ˽񤭹ि
ͥХåե˻ѤǤ֤Ǥ硢
(3) եǥץ顼ˤʤä
(åȤѥפξϡ³¾ü줿)

󤹤ȡ
.BR select ()
ʣΥեǥץδƻԤΤΤǡ
ԤɸŪ Unix Ǥ롣

եǥץ
.I եǥץ (file descriptor set)
ȸƤФ롣ơν
.B fd_set
Ȥ졢Ƥ
.BR FD_CLR (),
.BR FD_ISSET (),
.BR FD_SET (),
.BR FD_ZERO ()
ȤäޥˤäѹǤ롣
ǥץФƤϡ̾
.BR FD_ZERO ()
ǽ˻Ȥ
θǡƻоݤȤեǥץİ
.BR FD_SET ()
ɲä롣
.BR select ()
ϤνƤ򡢰ʹߤ˽Ҥ٤뵬§˽äƽ롣
.BR select ()
Ƥ塢եǥץޤ¸ߤƤ뤫ɤϡ
.BR FD_ISSET ()
ޥˤäĴ٤뤳ȤǤ롣
.BR FD_ISSET ()
ϤΥǥץ¸ߤƤ 0 ʳ֤ͤ
¸ߤƤʤ 0 ֤
.BR FD_CLR ()
Ͻ礫ΥեǥץκԤ
.SS 
.TP
\fIreadfds\fP
ν˴ޤޤ뤤줫Υեǥץ
ǡɤ߹ߤǽˤʤäɤƻ뤹롣
.BR select ()
ˡ\fIreadfds\fP Τ
.BR recv (2)
(åȤξ) 
.BR read (2)
(ѥסե롢åȤξ)
ˤäľɤ߹߲ǽʥեǥץʳ
礫롣
.TP
\fIwritefds\fP
ν˴ޤޤ뤤줫Υեǥץ
ǡ񤭹ॹڡ뤫ɤƻ뤹롣
.BR select ()
ˡ\fIwritefds\fP Τ
.BR send (2)
(åȤξ) 
.BR write (2)
(ѥסե롢åȤξ)
ˤäľ˽񤭹߲ǽʥեǥץʳ
礫롣
.TP
\fIexceptfds\fP
ν˴ޤޤ뤤줫Υեǥץ
㳰䥨顼Ƥ뤫ɤƻ뤹롣
Ϥα˲᤮
ºݤ \fIexceptfds\fP Ǵƻ뤷ƤΤ
\fIӰ賰 (out-of-band: OOB)\fP ǡʤΤ
OOB ǡϥåȤ \fBMSG_OOB\fP ե饰Ѥ롣
äơºݤˤ \fIexceptfds\fP ϥåȤˤŬѤǤʤ
ξܺ٤ˤĤƤ
.BR recv (2)

.BR send (2)
򸫤衣
.BR select ()
ˡ\fIexceptfds\fP Τ
OOB ǡɤ߹ߤǽˤʤäƤǥץʳ
礫롣
OOB ǡɤ߹
.RB ( recv (2)
ǹԤ)  1 ХȤǤʤ
OOB ǡν񤭹
.RB ( send (2)
ǹԤ) ϤĤǤǤ
 (block) 뤳Ȥʤ
äơåȤ OOB ǡν񤭹ߤǽǤ뤫ɤå
4 ܤνɬפʤΤǤ롣
.TP
\fInfds\fP
Ƥν˴ޤޤեǥץΤ
ͤΤΤ 1 ­Ǥ롣
ʤեǥץ򽸹˲äȤǡ
ƤΥեǥץ򸫤ƺͤᡢ
 1 ä \fInfds\fP Ȥ
.BR select ()
ϤʤȤʤȤȤ
.TP
\fIutimeout\fP
(ⵯʤä)
.BR select ()
Ԥĺ֤Ǥ롣
ͤ NULL Ϥȡ
.BR select ()
ϲ餫Υ٥ȤԤĤŤƤäߤ롣
\fIutimeout\fP  0 äˤ뤳ȤǤ
ξ
.BR select ()
ľ롣
¤ \fIstruct timeval\fP ϼΤ褦Ƥ:
.IP
.in +4n
.nf
struct timeval {
    time_t tv_sec;    /* seconds */
    long tv_usec;     /* microseconds */
};
.fi
.in
.TP
\fIntimeout\fP
ΰ \fIutimeout\fP Ʊ̣Ĥ
\fIstruct timespec\fP ϼ˼褦˥ʥä٤ġ
.in +4n
.nf
struct timespec {
    long tv_sec;    /* seconds */
    long tv_nsec;   /* nanoseconds */
};
.fi
.in
.TP
\fIsigmask\fP
ΰ
.BR pselect ()
μ¹˵Ĥ
ʥνݻ
.RB ( sigaddset (3)

.BR sigprocmask (2)
򻲾)ˤ NULL ϤȤǤ
ξϤδؿȤФȤ˵ĥʥνѹʤ
θ
.BR select ()
Ʊͤư򤹤롣
.SS ʥȥǡ٥ȤȤ߹碌
եǥץ顢ǡǤʤʥԤȤˤ
.BR pselect ()
Ȥɬפ롣ʥ򥤥٥ȤȤƼץϡ
񥷥ʥϥɥ򥰥Хʥե饰ΩƤ뤿˻Ȥ
ΥХʥե饰ϡ
Υ٥ȤץΥᥤ롼פ
ʤФʤʤȤ򼨤
ʥ
.BR select ()
(
.BR pselect ())

\fIerrno\fP  \fBEINTR\fP 򥻥åȤ뤳Ȥˤʤ롣
ʥ뤬ץΥᥤ롼פǽ뤿ˤϤưԲķǡ
줬ʤ
.BR select ()
ϱʱߤ³뤳Ȥˤʤ롣
ơᥤ롼פΤɤˤΥХե饰å
ʸȤ褦ǾͤƤߤʤȤʤ
֥ʥ뤬ʸθ塢
.BR select ()
夷
ɤʤΤ
ϡ֤
.BR select ()
ϡȤԤΥ٥ȤäȤƤ⡢
ʱߤפǤ롣
ζ֤
.BR pselect ()
ˤäƲǤ롣
.BR pselect ()
ϡʬȤʳǤϼʤʥ
ޥƽΤ˻ѤǤ롣
㤨СȤʤäƤ륤٥Ȥҥץνλξͤ褦
ᥤ롼פϤޤˡ \fBSIGCHLD\fP 
.BR sigprocmask (2)
ǥ֥å롣
.BR pselect ()
Ǥ \fBSIGCHLD\fP 򡢤ȤȤΥʥޥ
ȤäͭˤΤΥץϼΤ褦ˤʤ롣
.PP
.nf
int child_events = 0;

void
child_sig_handler(int x)
{
    child_events++;
    signal(SIGCHLD, child_sig_handler);
}

int
main(int argc, char **argv)
{
    sigset_t sigmask, orig_sigmask;

    sigemptyset(&sigmask);
    sigaddset(&sigmask, SIGCHLD);
    sigprocmask(SIG_BLOCK, &sigmask, &orig_sigmask);

    signal(SIGCHLD, child_sig_handler);

    for (;;) { /* main loop */
        for (; child_events > 0; child_events\-\-) {
            /* do event work here */
        }
        r = pselect(nfds, &rd, &wr, &er, 0, &orig_sigmask);

        /* main body of program */
    }
}
.fi
.SS 
ºݤΤȤ
.BR select ()
ϲʤΤ
ǥץϹʤȤɤ߽񤭤Ǥ󤸤ʤΡ
.BR select ()
νפʤȤϡʣΥǥץƱ˴ƻǤ
ʤưʤХץŬڤ˥꡼׾֤˰ܹԤȤˤΤ
.BR select ()
ѤСʣΥѥפ䥽åȤƱ˰ʤ
줬Ԥ롣Unix ץޤϡ
ʣΥեǥץϤƱ˰ͤФʤ餺
ǡήϴַŪǤ롢Ȥˤ褯в񤦡
ñ
.BR read (2)

.BR write (2)
Υ󥹤ǤϡΥΤɤ줫
եǥץΥǡԤäƥ֥åƤꡢ
¾Υեǥץˤϥǡ夷ƤΤ˻Ȥʤ
ȤȤˤʤäƤޤ
.BR select ()
ȤȤξ˸ŪнǤ롣

.BR select ()
Ȥäñ㤬
.BR select (2)
Υޥ˥奢ڡ˽񤫤Ƥ롣
.SS SELECT 
.BR select ()
ȤȤ¿οͤϡ򤷤ˤư˽Ф路Ū
ǤΤϰܿʤ褯Ƥ⥮ꥮΤΤˤʤäƤޤ
㤨С嵭Υץϡ
˴ޤޤեǥץ֥å⡼
.RB ( ioctl (2)
) ˤʤƤ⡢ɤˤ֥åʤ褦դƽ񤫤Ƥ롣
̯ʴְ㤤ˤäơ
.BR select ()
Ȥϴñ˼Ƥޤ
ǤǤϡ
.BR select ()
ȤȤդ٤׻ꥹȤ褦Ȼפ
.TP 4
1.
.BR select ()
ȤȤϡॢȤꤹ٤Ǥʤ
ǡ̵Ȥˤϡ
ʤΥץˤϲ⤹뤳Ȥ̵ϤǤ롣
ॢȤ˰¸ɤ̾ܿʤ
ǥХå񤷤ʤ롣
.TP
2.
Ҥ褦ˡ
ΨŪʥץ񤯤ˤ
.I nfds
ͤŬڤ˷׻ͿʤФʤʤ
.TP
3.
.BR select ()
νλ˷̤åơ
ŬڤбĤΤʤեǥץϡ
ɤνˤäƤϤʤʤ
Υ롼⻲ȡ
.TP
4.
.BR select ()
֤äˤϡƤνƤΥեǥץˤĤ
ɤ߽񤭲ǽʾ֤ˤʤäƤ뤫å٤Ǥ롣
.\" mtk, May 2006: the following isn't really true.
.\" Any file descriptor that is available
.\" for writing \fImust\fP be written to, and any file descriptor
.\" available for reading \fImust\fP be read, etc.
.TP
5.
.BR read (2),
.BR recv (2),
.BR write (2),
.BR send (2)
Ȥäؿϡ餬׵ᤷǡɤ߽񤭤ɬפ\fIʤ\fP
⤷ǡɤ߽񤭤ʤ顢ϥȥեå٤
ȥ꡼ब®ξϾȤϸ¤ʤ
δؿĥäƤ 1 ХȤǤʤ褦ʾ
θƤʤФʤʤ
.TP
6.
ǡ̤ȤϤäȤ狼äƤơ
٤ 1 ХȤɤ߽񤭤褦ʤȤϤƤϤʤʤ
ХåեεΥǡޤȤɤ߽񤭤ʤȡ
˸Ψ嵭ǤϥХåե 1024 ХȤˤƤ뤬
Υ礭Τϴñ
.TP
7.
.BR read (2),
.BR recv (2),
.BR write (2),
.BR send (2)
ʤɤδؿ
.BR select ()
ϡ
.I errno

.B EINTR "  " EAGAIN
.RB ( EWOULDBLOCK )
ˤ \-1 ֤Ȥ롣
Τ褦ʷ̤ФŬڤбƤʤФʤʤ
(嵭ǤϤƤʤ)
񤤤Ƥץबʥͽ꤬ʤС
.B EINTR
֤뤳ȤϤޤͤʤ
񤤤Ƥץ֥å I/O 򥻥åȤƤʤϡ
.B EAGAIN
֤뤳ȤϤʤǤʤ
ʤСΥ顼θɬפ롣
.TP
8.
褷ơĹ 0 ΥХåեꤷ
.BR read (2),
.BR recv (2),
.BR write (2),
.BR send (2)
ƤӽФƤϤʤʤ
.TP
9.
.BR read (2),
.BR recv (2),
.BR write (2),
.BR send (2)

\fB7.\fP ˼ʳΥ顼ǼԤ䡢
ϷϤδؿΰĤեɽ 0 ֤ϡ
Υǥץ⤦ select ϤƤ\fIʤʤ\fP
嵭ǤϡΥǥץ򤿤˥
ˤ \-1 򥻥åȤơ
줬˴ޤޤ³Τʤ褦ˤƤ롣
.TP
10.
ॢȤͤ
.BR select ()
Ƥ֤Ӥ˽٤Ǥ롣
OS ˤäƤ timeout ¤Τѹ礬뤫Ǥ롣
â
.BR pselect ()
ϼʬ timeout ¤Τѹ뤳ȤϤʤ
.TP
11.
ʹȤǤϡWindows Υåؤ
OOB ǡʤ餷
ޤեǥץåȤƤʤ褦
.BR select ()
ʤ餷
եǥץꤷʤ timeout Ȥϡ
1 ðʲ٤ǥץ򥹥꡼פˤˡʤΤ
(³򸫤)
.SS usleep ߥ졼
.BR usleep (3)
ؿʤƥǤϡ
ͭ¤ΥॢȤꤷեǥץåȤ
.BR select ()
ƤӽФȤǡѤǤ롣
ʲΤ褦ˤ롣
.PP
.nf
    struct timeval tv;
    tv.tv_sec = 0;
    tv.tv_usec = 200000;  /* 0.2 seconds */
    select(0, NULL, NULL, NULL, &tv);
.fi
.PP
â줬ưݾڤƤΤ Unix ƥ˸¤롣
.SH ֤
ȡ
.BR select ()
ϥեǥץ˻ĤäƤ
եǥץ֤

.BR select ()
ॢȤȡ֤ͤ 0 ˤʤ롣
λեǥץϤ٤ƶǤ
(ʤʤƥ⤢)

֤ͤ \-1 ξϥ顼̣
.I errno
Ŭڤ˥åȤ롣顼ä硢
֤줿Ƥ乽¤ \fIstruct timeout\fP Ƥ
̤ȤʤäƤꡢѤ٤ǤϤʤ

.BR pselect ()
Ϸ褷
.I ntimeout
ѹʤ
.SH 
Ū˸äơåȤ򥵥ݡȤƤΥڥ졼ƥ󥰥ƥ
.BR select ()
⥵ݡȤƤ롣
.BR select ()
ȤʤȤΤʣˤʤäƤޤץब¿
.BR select ()
ȤȡץޤåɡեIPCʥ롢궦ͭ
ȤäƤäʣˡDz褷褦Ȥ¿꤬
꤫ܿĸΨŪˡDzǤ롣
.PP
.BR poll (2)
ƥॳ
.BR select ()
ƱǽäƤꡢ
ޤФʥեǥץƻ뤹
餫Ψ褤
ߤǤϹѲǽǤ뤬
.BR select ()
̤ܿäƤ
.PP
Linux ȼ
.BR epoll (7)
API ϡ¿Υեǥץƻ뤹
.BR select (2)

.BR poll (2)
ΨŪʥ󥿥ե󶡤Ƥ롣
.SH 
.BR select ()
򼨤褤Ҳ𤹤롣
ʲΥꥹȤϡ TCP ݡȤ̤ΥݡȤžԤ
TCP եɥץǤ롣
.PP
.nf
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
#include <string.h>
#include <signal.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

static int forward_port;

#undef max
#define max(x,y) ((x) > (y) ? (x) : (y))

static int
listen_socket(int listen_port)
{
    struct sockaddr_in a;
    int s;
    int yes;

    if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        return \-1;
    }
    yes = 1;
    if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR,
            (char *) &yes, sizeof(yes)) < 0) {
        perror("setsockopt");
        close(s);
        return \-1;
    }
    memset(&a, 0, sizeof(a));
    a.sin_port = htons(listen_port);
    a.sin_family = AF_INET;
    if (bind(s, (struct sockaddr *) &a, sizeof(a)) < 0) {
        perror("bind");
        close(s);
        return \-1;
    }
    printf("accepting connections on port %d\\n", listen_port);
    listen(s, 10);
    return s;
}

static int
connect_socket(int connect_port, char *address)
{
    struct sockaddr_in a;
    int s;

    if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        close(s);
        return \-1;
    }

    memset(&a, 0, sizeof(a));
    a.sin_port = htons(connect_port);
    a.sin_family = AF_INET;

    if (!inet_aton(address, (struct in_addr *) &a.sin_addr.s_addr)) {
        perror("bad IP address format");
        close(s);
        return \-1;
    }

    if (connect(s, (struct sockaddr *) &a, sizeof(a)) < 0) {
        perror("connect()");
        shutdown(s, SHUT_RDWR);
        close(s);
        return \-1;
    }
    return s;
}

#define SHUT_FD1 {                      \\
        if (fd1 >= 0) {                 \\
            shutdown(fd1, SHUT_RDWR);   \\
            close(fd1);                 \\
            fd1 = \-1;                   \\
        }                               \\
    }

#define SHUT_FD2 {                      \\
        if (fd2 >= 0) {                 \\
            shutdown(fd2, SHUT_RDWR);   \\
            close(fd2);                 \\
            fd2 = \-1;                   \\
        }                               \\
    }

#define BUF_SIZE 1024

int
main(int argc, char **argv)
{
    int h;
    int fd1 = \-1, fd2 = \-1;
    char buf1[BUF_SIZE], buf2[BUF_SIZE];
    int buf1_avail, buf1_written;
    int buf2_avail, buf2_written;

    if (argc != 4) {
        fprintf(stderr,
                 "Usage\\n\\tfwd <listen-port> "
                 "<forward-to-port> <forward-to-ip-address>\\n");
        exit(EXIT_FAILURE);
    }

    signal(SIGPIPE, SIG_IGN);

    forward_port = atoi(argv[2]);

    h = listen_socket(atoi(argv[1]));
    if (h < 0)
        exit(EXIT_FAILURE);

    for (;;) {
        int r, nfds = 0;
        fd_set rd, wr, er;
        FD_ZERO(&rd);
        FD_ZERO(&wr);
        FD_ZERO(&er);
        FD_SET(h, &rd);
        nfds = max(nfds, h);
        if (fd1 > 0 && buf1_avail < BUF_SIZE) {
            FD_SET(fd1, &rd);
            nfds = max(nfds, fd1);
        }
        if (fd2 > 0 && buf2_avail < BUF_SIZE) {
            FD_SET(fd2, &rd);
            nfds = max(nfds, fd2);
        }
        if (fd1 > 0
            && buf2_avail \- buf2_written > 0) {
            FD_SET(fd1, &wr);
            nfds = max(nfds, fd1);
        }
        if (fd2 > 0
            && buf1_avail \- buf1_written > 0) {
            FD_SET(fd2, &wr);
            nfds = max(nfds, fd2);
        }
        if (fd1 > 0) {
            FD_SET(fd1, &er);
            nfds = max(nfds, fd1);
        }
        if (fd2 > 0) {
            FD_SET(fd2, &er);
            nfds = max(nfds, fd2);
        }

        r = select(nfds + 1, &rd, &wr, &er, NULL);

        if (r == \-1 && errno == EINTR)
            continue;
        if (r < 0) {
            perror("select()");
            exit(EXIT_FAILURE);
        }
        if (FD_ISSET(h, &rd)) {
            unsigned int l;
            struct sockaddr_in client_address;
            memset(&client_address, 0, l = sizeof(client_address));
            r = accept(h, (struct sockaddr *) &client_address, &l);
            if (r < 0) {
                perror("accept()");
            } else {
                SHUT_FD1;
                SHUT_FD2;
                buf1_avail = buf1_written = 0;
                buf2_avail = buf2_written = 0;
                fd1 = r;
                fd2 =
                    connect_socket(forward_port, argv[3]);
                if (fd2 < 0) {
                    SHUT_FD1;
                } else
                    printf("connect from %s\\n",
                            inet_ntoa(client_address.sin_addr));
            }
        }
/* NB: read oob data before normal reads */
        if (fd1 > 0)
            if (FD_ISSET(fd1, &er)) {
                char c;
                errno = 0;
                r = recv(fd1, &c, 1, MSG_OOB);
                if (r < 1) {
                    SHUT_FD1;
                } else
                    send(fd2, &c, 1, MSG_OOB);
            }
        if (fd2 > 0)
            if (FD_ISSET(fd2, &er)) {
                char c;
                errno = 0;
                r = recv(fd2, &c, 1, MSG_OOB);
                if (r < 1) {
                    SHUT_FD1;
                } else
                    send(fd1, &c, 1, MSG_OOB);
            }
        if (fd1 > 0)
            if (FD_ISSET(fd1, &rd)) {
                r =
                    read(fd1, buf1 + buf1_avail,
                          BUF_SIZE \- buf1_avail);
                if (r < 1) {
                    SHUT_FD1;
                } else
                    buf1_avail += r;
            }
        if (fd2 > 0)
            if (FD_ISSET(fd2, &rd)) {
                r =
                    read(fd2, buf2 + buf2_avail,
                          BUF_SIZE \- buf2_avail);
                if (r < 1) {
                    SHUT_FD2;
                } else
                    buf2_avail += r;
            }
        if (fd1 > 0)
            if (FD_ISSET(fd1, &wr)) {
                r =
                    write(fd1, buf2 + buf2_written,
                           buf2_avail \- buf2_written);
                if (r < 1) {
                    SHUT_FD1;
                } else
                    buf2_written += r;
            }
        if (fd2 > 0)
            if (FD_ISSET(fd2, &wr)) {
                r =
                    write(fd2, buf1 + buf1_written,
                           buf1_avail \- buf1_written);
                if (r < 1) {
                    SHUT_FD2;
                } else
                    buf1_written += r;
            }
/* check if write data has caught read data */
        if (buf1_written == buf1_avail)
            buf1_written = buf1_avail = 0;
        if (buf2_written == buf2_avail)
            buf2_written = buf2_avail = 0;
/* one side has closed the connection, keep
   writing to the other side until empty */
        if (fd1 < 0 && buf1_avail \- buf1_written == 0) {
            SHUT_FD2;
        }
        if (fd2 < 0 && buf2_avail \- buf2_written == 0) {
            SHUT_FD1;
        }
    }
    exit(EXIT_SUCCESS);
}
.fi
.PP
嵭ΥץϡۤȤɤμ TCP ³եɤ롣
.B telnet
ФˤäѤ OOB ʥǡⰷ롣
ΥץϡǡեƱȤ
䤳Ǥ롣
.BR fork (2)
Ȥäơƥȥ꡼ऴȤѤΥåɤѤۤΨŪ
Ȥͤ⤤뤫⤷ʤϹͤƤꤺäȤ䤳
뤤ϡ
.BR ioctl (2)
Ȥä֥å I/O 򥻥åȤɤȤǥ⤢
ˤºݤˤ꤬ꡢॢȤΨŪ˵äƤޤ

Υץϰ٤ˤҤȤİʾƱ³򰷤ȤϤǤʤ
ͤ˳ĥΤϴñǡХåեΥ󥯥ꥹȤ
(³ȤˤҤȤĤ) ȤФ褤
ΤΤǤϡ³ȸŤ³Ƥޤ
.SH Ϣ
.BR accept (2),
.BR connect (2),
.BR ioctl (2),
.BR poll (2),
.BR read (2),
.BR recv (2),
.BR select (2),
.BR send (2),
.BR sigprocmask (2),
.BR write (2),
.BR sigaddset (3),
.BR sigdelset (3),
.BR sigemptyset (3),
.BR sigfillset (3),
.BR sigismember (3),
.BR epoll (7)
.\" .SH AUTHORS
.\" This man page was written by Paul Sheer.