[linuxjm/LDP_man-pages.git] / draft / man2 / select.2

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.\" This manpage is copyright (C) 1992 Drew Eckhardt,
.\"                 copyright (C) 1995 Michael Shields.
.\"
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
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.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1995-05-18 by Jim Van Zandt <jrv@vanzandt.mv.com>
.\" Sun Feb 11 14:07:00 MET 1996  Martin Schulze  <joey@linux.de>
.\"     * layout slightly modified
.\"
.\" Modified Mon Oct 21 23:05:29 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified Thu Feb 24 01:41:09 CET 2000 by aeb
.\" Modified Thu Feb  9 22:32:09 CET 2001 by bert hubert <ahu@ds9a.nl>, aeb
.\" Modified Mon Nov 11 14:35:00 PST 2002 by Ben Woodard <ben@zork.net>
.\" 2005-03-11, mtk, modified pselect() text (it is now a system
.\"     call in 2.6.16.
.\"
.\" Japanese Version Copyright (c) 1997 HANATAKA Shinya all rights reserved.
.\" Translated 1997-02-23, HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\" Modified 2000-03-12, HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\" Updated & Modified 2001-06-04, Yuichi SATO <ysato@h4.dion.ne.jp>
.\" Updated & Modified 2001-07-01, Yuichi SATO
.\" Updated & Modifedd 2002-01-14, Yuichi SATO
.\" Updated 2002-09-24, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2003-01-19, Akihiro MOTOKI
.\" Updated 2005-03-17, Akihiro MOTOKI
.\" Updated 2006-04-16, Akihiro MOTOKI, LDP v2.28
.\" Updated 2006-07-23, Akihiro MOTOKI, LDP v2.36
.\" Updated 2007-09-08, Akihiro MOTOKI, LDP v2.64
.\" Updated 2008-08-06, Akihiro MOTOKI, LDP v3.05
.\"
.\"WORD:        synchronous             Ʊ´ü¤µ¤»¤ë
.\"WORD:        multiplexing            ¿½Å²½
.\"WORD:        file descriptor         ¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿
.\"WORD:        descriptor              µ­½Ò»Ò
.\"WORD:        macro                   ¥Þ¥¯¥í
.\"WORD:        block                   Ää»ß(block)
.\"WORD:        block                   ¶Ø»ß(block)
.\"WORD:        signal                  ¥·¥°¥Ê¥ë
.\"WORD:        timeout                 »þ´ÖÀÚ¤ì(timeout)
.\"WORD:        portable                °Ü¿¢À­¤Î¤¢¤ë
.\"
.TH SELECT 2 2008-12-05 "Linux" "Linux Programmer's Manual"
.\"O .SH NAME
.SH ̾Á°
.\"O select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO \-
.\"O synchronous I/O multiplexing
select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO \- ¿½Å²½¤µ¤ì¤¿ I/O ¤ÎƱ´ü¤ò¤È¤ë
.\"O .SH SYNOPSIS
.SH ½ñ¼°
.nf
.\"O /* According to POSIX.1-2001 */
/* POSIX.1-2001 ¤Ë½¾¤¦¾ì¹ç */
.br
.B #include <sys/select.h>
.sp
.\"O /* According to earlier standards */
/* °ÊÁ°¤Îµ¬³Ê¤Ë½¾¤¦¾ì¹ç */
.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 *" timeout );
.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 *" timeout ,
.BI "            const sigset_t *" sigmask );
.fi
.sp
.in -4n
.\"O Feature Test Macro Requirements for glibc (see
.\"O .BR feature_test_macros (7)):
glibc ¸þ¤±¤Îµ¡Ç½¸¡ºº¥Þ¥¯¥í¤ÎÍ×·ï
.RB ( feature_test_macros (7)
»²¾È):
.in
.sp
.BR pselect ():
_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O .BR select ()
.\"O and
.\"O .BR pselect ()
.\"O allow a program to monitor multiple file descriptors,
.\"O waiting until one or more of the file descriptors become "ready"
.\"O for some class of I/O operation (e.g., input possible).
.\"O A file descriptor is considered ready if it is possible to
.\"O perform the corresponding I/O operation (e.g.,
.\"O .BR read (2))
.\"O without blocking.
.BR select ()
¤ä
.BR pselect ()
¤ò»È¤¦¤È¡¢¥×¥í¥°¥é¥à¤ÇÊ£¿ô¤Î¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤ò´Æ»ë¤·¡¢
°ì¤Ä°Ê¾å¤Î¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬¤¢¤ë¼ï¤Î I/O Áàºî¤Î
¡Öready (½àÈ÷¤¬¤Ç¤­¤¿)¡×¾õÂÖ (Î㤨¤Ð¡¢Æɤ߹þ¤ß²Äǽ¤Ë¤Ê¤Ã¤¿¾õÂÖ)
¤Ë¤Ê¤ë¤Þ¤ÇÂԤĤ³¤È¤¬¤Ç¤­¤ë¡£
¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬ ready (½àÈ÷¤¬¤Ç¤­¤¿) ¤È¤Ï¡¢
Âбþ¤¹¤ë I/O Áàºî (Î㤨¤Ð
.BR read (2)
¤Ê¤É) ¤¬Ää»ß (block) ¤Ê¤·¤Ë¼Â¹Ô²Äǽ¤Ê¾õÂ֤ˤ¢¤ë¤³¤È¤ò°ÕÌ£¤¹¤ë¡£
.PP
.\"O The operation of
.\"O .BR select ()
.\"O and
.\"O .BR pselect ()
.\"O is identical, with three differences:
.BR select ()
¤È
.BR pselect ()
¤ÎÆ°ºî¤ÏƱ¤¸¤Ç¤¢¤ë¤¬¡¢°Ê²¼¤Î 3 ÅÀ¤¬°Û¤Ê¤ë:
.TP
(i)
.\"O .BR select ()
.\"O uses a timeout that is a
.\"O .I struct timeval
.\"O (with seconds and microseconds), while
.\"O .BR pselect ()
.\"O uses a
.\"O .I struct timespec
.\"O (with seconds and nanoseconds).
.BR select ()
¤Ç¤Ï¡¢¥¿¥¤¥à¥¢¥¦¥È»þ´Ö¤Î»ØÄê¤Ë¹½Â¤ÂÎ
.I struct timeval
(Éᦥޥ¤¥¯¥íÉÃñ°Ì) ¤òÍѤ¤¤ë¡£
°ìÊý¡¢
.BR pselect ()
´Ø¿ô¤Ç¤Ï¡¢¹½Â¤ÂÎ
.I struct timespec
(ÉᦥʥÎÉÃñ°Ì) ¤òÍѤ¤¤ë¡£
.TP
(ii)
.\"O .BR select ()
.\"O may update the
.\"O .I timeout
.\"O argument to indicate how much time was left.
.\"O .BR pselect ()
.\"O does not change this argument.
.BR select ()
¤Ï»Ä¤ê»þ´Ö¤ò¼¨¤¹
.I timeout
°ú¤­¿ô¤ò¹¹¿·¤¹¤ë¤³¤È¤¬¤¢¤ë¡£
.BR pselect ()
¤Ï¤³¤Î°ú¤­¿ô¤òÊѹ¹¤·¤Ê¤¤¡£
.TP
(iii)
.\"O The
.\"O .BR select ()
.\"O has no
.\"O .I sigmask
.\"O argument, and behaves as
.\"O .BR pselect ()
.\"O called with NULL
.\"O .IR sigmask .
.BR select ()
¤Ï
.I sigmask
°ú¤­¿ô¤ò»ý¤¿¤Ê¤¤¡£¤½¤ÎÆ°ºî¤Ï
.I sigmask
¤Ë NULL ¤ò»ØÄꤷ¤¿¾ì¹ç¤Î
.BR pselect ()
¤ÈƱ¤¸¤Ç¤¢¤ë¡£
.PP
.\"O Three independent sets of file descriptors are watched.
.\"O Those listed in
.\"O .I readfds
.\"O will be watched to see if characters become
.\"O available for reading (more precisely, to see if a read will not
.\"O block; in particular, a file descriptor is also ready on end-of-file),
.\"O those in
.\"O .I writefds
.\"O will be watched to see if a write will not block, and
.\"O those in
.\"O .I exceptfds
.\"O will be watched for exceptions.
.\"O On exit, the sets are modified in place
.\"O to indicate which file descriptors actually changed status.
.\"O Each of the three file descriptor sets may be specified as NULL
.\"O if no file descriptors are to be watched for the corresponding class
.\"O of events.
3 ¤Ä¤ÎÆÈΩ¤·¤¿¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿½¸¹ç¤Î´Æ»ë¤ò¹Ô¤¦¡£
.I readfds
¤ËÆþ¤ì¤é¤ì¤¿¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Ë¤Ä¤¤¤Æ¤Ï¡¢Æɤ߹þ¤ß¤¬²Äǽ¤«¤É¤¦¤«¤ò
´Æ»ë¤¹¤ë (¤è¤êÀµ³Î¤Ë¤¤¤¦¤È¡¢Ää»ß (block) ¤Ê¤·¤ÇÆɤळ¤È¤¬¤Ç¤­¤ë¤«¤ò
Ä´¤Ù¤ë¡£¥Õ¥¡¥¤¥ë¤Î½ªÃ¼ (end-of-file) ¤Î¾ì¹ç¤â¡¢
¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤ÏÆɤ߹þ¤ß²Äǽ¤È¤·¤Æ°·¤ï¤ì¤ë)¡£
.I writefds
¤ËÆþ¤ì¤é¤ì¤¿¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Ë¤Ä¤¤¤Æ¤Ï¡¢Ää»ß¤»¤º¤Ë½ñ¤­¹þ¤ß¤¬
²Äǽ¤«¤É¤¦¤«¤ò´Æ»ë¤¹¤ë¡£
.I exceptfds
¤Ë¤¢¤ë¤â¤Î¤Ë¤Ä¤¤¤Æ¤Ï¡¢Îã³°¤Î´Æ»ë¤ò¹Ô¤Ê¤¦¡£¥·¥¹¥Æ¥à¥³¡¼¥ë½ªÎ»»þ¤Ë¡¢
¤É¤Î¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Î¾õÂÖ¤¬¼ÂºÝ¤ËÊѲ½¤·¤¿¤«¼¨¤¹¤¿¤á¤Ë¡¢
½¸¹ç¤ÎÆâÍƤ¬Êѹ¹¤µ¤ì¤ë¡£
¤¢¤ë¼ïÊ̤Υ¤¥Ù¥ó¥È¤ò´Æ»ë¤·¤¿¤¤¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬°ì¤Ä¤â¤Ê¤¤¾ì¹ç¤Ë¤Ï¡¢
Âбþ¤¹¤ë¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿½¸¹ç¤Ë NULL ¤ò»ØÄꤹ¤ë¤³¤È¤¬¤Ç¤­¤ë¡£
.PP
.\"O Four macros are provided to manipulate the sets.
½¸¹ç¤òÁàºî¤¹¤ë¤¿¤á¤Ë 4 ¤Ä¤Î¥Þ¥¯¥í¤¬Ä󶡤µ¤ì¤Æ¤¤¤ë¡£
.\"O .BR FD_ZERO ()
.\"O clears a set.
.BR FD_ZERO ()
¤Ï½¸¹ç¤ò¾Ãµî¤¹¤ë¡£
.\"O .BR FD_SET ()
.\"O and
.\"O .BR FD_CLR ()
.\"O respectively add and remove a given file descriptor from a set.
.BR FD_SET ()
¤È
.BR FD_CLR ()
¤Ï¤½¤ì¤¾¤ì»ØÄꤷ¤¿¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Î½¸¹ç¤Ø¤ÎÄɲᢺï½ü¤ò¹Ô¤¦¡£
.\"O .BR FD_ISSET ()
.\"O tests to see if a file descriptor is part of the set;
.\"O this is useful after
.\"O .BR select ()
.\"O returns.
.BR FD_ISSET ()
¤Ï½¸¹ç¤Ë¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬¤¢¤ë¤«¤É¤¦¤«Ä´¤Ù¤ë; 
¤³¤Î¥Þ¥¯¥í¤Ï
.BR select ()
¤¬½ªÎ»¤·¤¿¸å¤Ë»È¤¦¤ÈÊØÍø¤Ç¤¢¤ë¡£
.PP
.\"O .I nfds
.\"O is the highest-numbered file descriptor in any of the three sets, plus 1.
.I nfds
¤Ï 3 ¤Ä¤Î½¸¹ç¤Ë´Þ¤Þ¤ì¤ë¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤ÎºÇÂçÃÍ¤Ë 1 ¤ò­¤·¤¿¤â¤Î¤Ç¤¢¤ë¡£
.PP
.\"O .I timeout
.\"O is an upper bound on the amount of time elapsed before
.\"O .BR select ()
.\"O returns.
.\"O If both fields of the
.\"O .I timeval
.\"O stucture are zero, then
.\"O .BR select ()
.\"O returns immediately.
.\"O (This is useful for polling.)
.\"O If
.\"O .I timeout
.\"O is NULL (no timeout),
.\"O .BR select ()
.\"O can block indefinitely.
.I timeout
¤Ï
.BR select ()
¤¬Éüµ¢¤¹¤ë¤Þ¤Ç¤Î·Ð²á»þ´Ö¤Î¾å¸Â¤Ç¤¢¤ë¡£
.I timeval
¹½Â¤ÂΤÎξÊý¤Î¥Õ¥£¡¼¥ë¥É¤¬ 0 ¤Î¾ì¹ç¡¢
.BR select ()
¤Ï¤¹¤°¤ËÉüµ¢¤¹¤ë
(¤³¤Îµ¡Ç½¤Ï¥Ý¡¼¥ê¥ó¥° (polling) ¤ò¹Ô¤¦¤Î¤ËÊØÍø¤Ç¤¢¤ë)¡£
.I timeout
¤Ë NULL (¥¿¥¤¥à¥¢¥¦¥È¤Ê¤·)
¤¬»ØÄꤵ¤ì¤ë¤È¡¢
.BR select ()
¤Ï̵´ü¸Â¤ËÄä»ß (block) ¤¹¤ë¡£
.PP
.\"O .I sigmask
.\"O is a pointer to a signal mask (see
.\"O .BR sigprocmask (2));
.\"O if it is not NULL, then
.\"O .BR pselect ()
.\"O first replaces the current signal mask by the one pointed to by
.\"O .IR sigmask ,
.\"O then does the "select" function, and then restores the original
.\"O signal mask.
.I sigmask
¤Ï¡¢¥·¥°¥Ê¥ë¥Þ¥¹¥¯
.RB ( sigprocmask (2)
¤ò»²¾È) ¤Ø¤Î¥Ý¥¤¥ó¥¿¤Ç¤¢¤ë¡£
.I sigmask
¤¬ NULL ¤Ç¤Ê¤¤¾ì¹ç¡¢
.BR pselect ()
¤Ï
.I sigmask
¤¬»Ø¤·¤Æ¤¤¤ë¥·¥°¥Ê¥ë¥Þ¥¹¥¯¤Ç¸½ºß¤Î¥·¥°¥Ê¥ë¥Þ¥¹¥¯¤òÃÖ¤­´¹¤¨¤Æ¤«¤é¡¢
"select" ´Ø¿ô¤ò¼Â¹Ô¤·¡¢
½ªÎ»¸å¤Ë¥·¥°¥Ê¥ë¥Þ¥¹¥¯¤ò¸µ¤Î¥·¥°¥Ê¥ë¥Þ¥¹¥¯¤ËÌ᤹¡£
.PP
.\"O Other than the difference in the precision of the
.\"O .I timeout
.\"O argument, the following
.\"O .BR pselect ()
.\"O call:
.I timeout
°ú¤­¿ô¤ÎÀºÅ٤ΰ㤤¤ò½ü¤¯¤È¡¢°Ê²¼¤Î
.BR pselect ()
¤Î¸Æ¤Ó½Ð¤·¤Ï¡¢
.nf

    ready = pselect(nfds, &readfds, &writefds, &exceptfds,
                    timeout, &sigmask);

.fi
.\"O is equivalent to
.\"O .I atomically
.\"O executing the following calls:
¼¡¤Î¥³¡¼¥ë¤ò
.I atomic
¤Ë¼Â¹Ô¤¹¤ë¤Î¤ÈÅù²Á¤Ç¤¢¤ë¡£
.nf

    sigset_t origmask;

    sigprocmask(SIG_SETMASK, &sigmask, &origmask);
    ready = select(nfds, &readfds, &writefds, &exceptfds, timeout);
    sigprocmask(SIG_SETMASK, &origmask, NULL);
.fi
.PP
.\"O The reason that
.\"O .BR pselect ()
.\"O is needed is that if one wants to wait for either a signal
.\"O or for a file descriptor to become ready, then
.\"O an atomic test is needed to prevent race conditions.
.\"O (Suppose the signal handler sets a global flag and
.\"O returns.
.\"O Then a test of this global flag followed by a call of
.\"O .BR select ()
.\"O could hang indefinitely if the signal arrived just after the test
.\"O but just before the call.
.BR pselect ()
¤¬É¬ÍפˤʤëÍýͳ¤Ï¡¢¥·¥°¥Ê¥ë¤ä¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Î¾õÂÖÊѲ½¤ò
ÂÔ¤Á¤¿¤¤¤È¤­¤Ë¤Ï¡¢¶¥¹ç¾õÂÖ¤òÈò¤±¤ë¤¿¤á¤Ë atomic ¤Ê¥Æ¥¹¥È¤¬É¬Íפˤʤë
¤«¤é¤Ç¤¢¤ë¡£
(¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤¬Âç°è¥Õ¥é¥°¤òÀßÄꤷ¤ÆÌá¤ë¾ì¹ç¤ò¹Í¤¨¤Æ¤ß¤è¤¦¡£
¤³¤ÎÂç°è¥Õ¥é¥°¤Î¥Æ¥¹¥È¤Ë³¤±¤Æ
.BR select ()
¤ò¸Æ¤Ó½Ð¤¹¤È¡¢
¥·¥°¥Ê¥ë¤¬¥Æ¥¹¥È¤Îľ¸å¤«¤Ä¸Æ¤Ó½Ð¤·¤ÎľÁ°¤ËÆϤ¤¤¿»þ¤Ë¤Ï
.BR select ()
¤Ï±Êµ×¤Ë¥Ï¥ó¥°¤·¤Æ¤·¤Þ¤¦¤«¤â¤·¤ì¤Ê¤¤¡£
.\"O By contrast,
.\"O .BR pselect ()
.\"O allows one to first block signals, handle the signals that have come in,
.\"O then call
.\"O .BR pselect ()
.\"O with the desired
.\"O .IR sigmask ,
.\"O avoiding the race.)
°ìÊý¡¢
.BR pselect ()
¤ò»È¤¦¤È¡¢¤Þ¤º¥·¥°¥Ê¥ë¤ò¶Ø»ß (block) ¤·¤Æ¡¢Æþ¤Ã¤Æ¤¯¤ë¥·¥°¥Ê¥ë¤òÁàºî¤·¡¢
˾¤ß¤Î
.I sigmask
¤Ç
.BR pselect ()
¤ò¸Æ¤Ó½Ð¤¹¤³¤È¤Ç¡¢Á°µ­¤Î¶¥¹ç¤òÈò¤±¤ë¤³¤È¤¬¤Ç¤­¤ë¡£)
.\"O .SS "The timeout"
.SS ¥¿¥¤¥à¥¢¥¦¥È
.\"O The time structures involved are defined in
.\"O .I <sys/time.h>
.\"O and look like
¤³¤ì¤é¤Î´Ø¿ô¤Ç»ÈÍѤµ¤ì¤ë»þ´Ö´ØÏ¢¤Î¹½Â¤ÂΤϡ¢
.I <sys/time.h>
¤Ç°Ê²¼¤Î¤è¤¦¤ËÄêµÁ¤µ¤ì¤Æ¤¤¤ë¡£

.\"O .in +4n
.\"O .nf
.\"O struct timeval {
.\"O     long    tv_sec;         /* seconds */
.\"O     long    tv_usec;        /* microseconds */
.\"O };
.\"O .fi
.\"O .in
.in +4n
.nf
struct timeval {
    long    tv_sec;         /* ÉÃ */
    long    tv_usec;        /* ¥Þ¥¤¥¯¥íÉà */
};
.fi
.in

.\"O and
.\"O
.\"O .in +4n
.\"O .nf
.\"O struct timespec {
.\"O     long    tv_sec;         /* seconds */
.\"O     long    tv_nsec;        /* nanoseconds */
.\"O };
.\"O .fi
.\"O .in
.in +4n
.nf
struct timespec {
    long    tv_sec;         /* ÉÃ */
    long    tv_nsec;        /* ¥Ê¥ÎÉà */
};
.fi
.in

.\"O (However, see below on the POSIX.1-2001 versions.)
(POSIX.1-2001 ¤Ç¤ÎÄêµÁ¤Ë¤Ä¤¤¤Æ¤Ï²¼µ­¤Î¡ÖÃí°Õ¡×¤ò»²¾È)
.PP
.\"O Some code calls
.\"O .BR select ()
.\"O with all three sets empty,
.\"O .I nfds
.\"O zero, and a non-NULL
.\"O .I timeout
.\"O as a fairly portable way to sleep with subsecond precision.
ÉÃñ°Ì°Ê²¼¤ÎÀºÅ٤ǥ¹¥ê¡¼¥×¤ò¼Â¸½¤¹¤ë
°Ü¿¢À­¤Î¹â¤¤ÊýË¡¤È¤·¤Æ¡¢
3 ¤Ä¤Î½¸¹çÁ´¤Æ¤ò¶õ¡¢
.I nfds
¤ò 0 ¡¢
.I timeout
¤ò NULL ¤Ç¤Ê¤¤ÃͤËÀßÄꤷ¤Æ
.BR select ()
¤ò¸Æ¤Ó½Ð¤¹¤È¤¤¤¦ÊýË¡¤ò»È¤Ã¤Æ¤¤¤ë¥³¡¼¥É¤â¤¢¤ë¡£
.PP
.\"O On Linux,
.\"O .BR select ()
.\"O modifies
.\"O .I timeout
.\"O to reflect the amount of time not slept; most other implementations
.\"O do not do this.
.\"O (POSIX.1-2001 permits either behavior.)
.\"O This causes problems both when Linux code which reads
.\"O .I timeout
.\"O is ported to other operating systems, and when code is ported to Linux
.\"O that reuses a \fIstruct timeval\fP for multiple
.\"O .BR select ()s
.\"O in a loop without reinitializing it.
.\"O Consider
.\"O .I timeout
.\"O to be undefined after
.\"O .BR select ()
.\"O returns.
Linux ¤Ç¤Ï¡¢
.BR select ()
¤Ï
.I timeout
¤òÊѹ¹¤·¡¢»Ä¤ê¤ÎÄä»ß»þ´Ö¤òÈ¿±Ç¤¹¤ë¤è¤¦¤Ë¤Ê¤Ã¤Æ¤¤¤ë¤¬¡¢
¾¤Î¤Û¤È¤ó¤É¤Î¼ÂÁõ¤Ç¤Ï¤³¤Î¤è¤¦¤Ë¤Ê¤Ã¤Æ¤¤¤Ê¤¤
(POSIX.1-2001 ¤Ï¤É¤Á¤é¤ÎÆ°ºî¤âǧ¤á¤Æ¤¤¤ë)¡£
¤³¤Î¤¿¤á¡¢
.I timeout
¤ò»²¾È¤·¤Æ¤¤¤ë Linux ¤Î¥³¡¼¥É¤ò¾¤Î¥ª¥Ú¥ì¡¼¥Æ¥£¥ó¥°¡¦¥·¥¹¥Æ¥à¤Ø
°Ü¿¢¤¹¤ë¾ì¹ç¡¢ÌäÂ꤬µ¯¤³¤ë¡£
¤Þ¤¿¡¢¥ë¡¼¥×¤ÎÃæ¤Ç \fItimeval\fP ¹½Â¤ÂΤò½é´ü²½¤»¤º¤Ë¤½¤Î¤Þ¤ÞºÆÍøÍѤ·¤Æ
.BR select ()
¤òÊ£¿ô²ó¹Ô¤Ê¤Ã¤Æ¤¤¤ë¥³¡¼¥É¤ò Linux ¤Ø°Ü¿¢¤¹¤ë¾ì¹ç¤Ë¤â¡¢ÌäÂ꤬µ¯¤³¤ë¡£
.BR select ()
¤«¤éÉüµ¢¤·¤¿¸å¤Ï
.I timeout
¤Ï̤ÄêµÁ¤Ç¤¢¤ë¤È¹Í¤¨¤ë¤Ù¤­¤Ç¤¢¤ë¡£
.\"O .\" .PP - it is rumored that:
.\"O .\" On BSD, when a timeout occurs, the file descriptor bits are not changed.
.\"O .\" - it is certainly true that:
.\"O .\" Linux follows SUSv2 and sets the bit masks to zero upon a timeout.
.\" .PP
.\" ¡ÖBSD ¤Ç¤Ï¥¿¥¤¥à¥¢¥¦¥È¤¬µ¯¤³¤Ã¤Æ¤â¡¢
.\" ¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¥Ó¥Ã¥È¤ÏÊѤï¤é¤Ê¤¤¡×¤Èʹ¤¤¤¿¤³¤È¤¬¤¢¤ë¡£
.\" ¡ÖLinux ¤Ï SUSv2 ¤Ë½¾¤Ã¤Æ¤ª¤ê¡¢
.\" ¥¿¥¤¥à¥¢¥¦¥È¤ÎºÝ¤Ë¤Ï¥Ó¥Ã¥È¥Þ¥¹¥¯¤ò 0 ¤Ë¤¹¤ë¡×¤È¤¤¤¦¤Î¤Ï³Î¤«¤Ë»ö¼Â¤Ç¤¢¤ë¡£
.\"O .SH "RETURN VALUE"
.SH ÊÖ¤êÃÍ
.\"O On success,
.\"O .BR select ()
.\"O and
.\"O .BR pselect ()
.\"O return the number of file descriptors contained in the three returned
.\"O descriptor sets (that is, the total number of bits that are set in
.\"O .IR readfds ,
.\"O .IR writefds ,
.\"O .IR exceptfds )
.\"O which may be zero if the timeout expires before anything interesting happens.
À®¸ù¤·¤¿¾ì¹ç¡¢
.BR select ()
¤È
.BR pselect ()
¤Ï¹¹¿·¤µ¤ì¤¿ 3 ¤Ä¤Î¥Ç¥£¥¹¥¯¥ê¥×¥¿½¸¹ç¤Ë´Þ¤Þ¤ì¤Æ¤¤¤ë
¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Î¿ô (¤Ä¤Þ¤ê¡¢
.IR readfds ,
.IR writefds ,
.I exceptfds
Ãæ¤Î 1 ¤Ë¤Ê¤Ã¤Æ¤¤¤ë¥Ó¥Ã¥È¤ÎÁí¿ô) ¤òÊÖ¤¹¡£
²¿¤âµ¯¤³¤é¤º¤Ë»þ´ÖÀÚ¤ì¤Ë¤Ê¤Ã¤¿¾ì¹ç¡¢
¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Î¿ô¤Ï 0 ¤Ë¤Ê¤ë¤³¤È¤â¤¢¤ë¡£
.\"O On error, \-1 is returned, and
.\"O .I errno
.\"O is set appropriately; the sets and
.\"O .I timeout
.\"O become undefined, so do not
.\"O rely on their contents after an error.
¥¨¥é¡¼¤Ê¤é¤Ð \-1 ¤òÊÖ¤·¡¢
.I errno
¤ËŬÀÚ¤ÊÃͤ¬ÀßÄꤵ¤ì¤ë; ½¸¹ç¤È
.I timeout
¤Ï̤ÄêµÁ¤È¤Ê¤ë¤Î¤Ç¡¢¥¨¥é¡¼¤¬µ¯¤³¤Ã¤¿¸å¤Ï¤½¤ì¤é¤ÎÆâÍƤò¿®Íꤷ¤Æ¤Ï¤Ê¤é¤Ê¤¤¡£
.\"O .SH ERRORS
.SH ¥¨¥é¡¼
.TP
.B EBADF
.\"O An invalid file descriptor was given in one of the sets.
.\"O (Perhaps a file descriptor that was already closed,
.\"O or one on which an error has occurred.)
¤¤¤º¤ì¤«¤Î½¸¹ç¤Ë̵¸ú¤Ê¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬»ØÄꤵ¤ì¤¿
(¤ª¤½¤é¤¯¤Ï¡¢¤¹¤Ç¤Ë¥¯¥í¡¼¥º¤µ¤ì¤¿¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤«¡¢
¥¨¥é¡¼¤¬È¯À¸¤·¤¿¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬»ØÄꤵ¤ì¤¿)¡£
.TP
.B EINTR
.\"O A signal was caught; see
.\"O .BR signal (7).
¥·¥°¥Ê¥ë¤ò¼õ¿®¤·¤¿¡£
.TP
.B EINVAL
.\"O .I nfds
.\"O is negative or the value contained within
.\"O .I timeout
.\"O is invalid.
.I n
¤¬Éé¡¢¤Þ¤¿¤Ï
.I timeout
¤ËÆþ¤Ã¤Æ¤¤¤ëÃͤ¬ÉÔÀµ¤Ç¤¢¤ë¡£
.TP
.B ENOMEM
.\"O unable to allocate memory for internal tables.
ÆâÉô¥Æ¡¼¥Ö¥ë¤Ë¥á¥â¥ê¤ò³ä¤êÅö¤Æ¤ë¤³¤È¤¬¤Ç¤­¤Ê¤«¤Ã¤¿¡£
.\"O .SH VERSIONS
.SH ¥Ð¡¼¥¸¥ç¥ó
.\"O .BR pselect ()
.\"O was added to Linux in kernel 2.6.16.
.BR pselect ()
¤Ï¥«¡¼¥Í¥ë 2.6.16 ¤Ç Linux ¤ËÄɲ䵤줿¡£
.\"O Prior to this,
.\"O .BR pselect ()
.\"O was emulated in glibc (but see BUGS).
¤½¤ì°ÊÁ°¤Ï¡¢
.BR pselect ()
¤Ï glibc ¤Ç¥¨¥ß¥å¥ì¡¼¥È¤µ¤ì¤Æ¤¤¤¿ (¡Ö¥Ð¥°¡×¤Î¾Ï¤ò»²¾È)¡£
.\"O .SH "CONFORMING TO"
.SH ½àµò
.\"O .BR select ()
.\"O conforms to POSIX.1-2001 and
.\"O 4.4BSD
.\"O .RB ( select ()
.\"O first appeared in 4.2BSD).
.\"O Generally portable to/from
.\"O non-BSD systems supporting clones of the BSD socket layer (including
.\"O System V variants).
.\"O However, note that the System V variant typically
.\"O sets the timeout variable before exit, but the BSD variant does not.
.BR select ()
¤Ï POSIX.1-2001 ¤È 4.4BSD
.RB ( select ()
¤Ï 4.2BSD ¤ÇºÇ½é¤ËÅо줷¤¿) ¤Ë½àµò¤¹¤ë¡£
BSD ¥½¥±¥Ã¥ÈÁؤΥ¯¥í¡¼¥ó¤ò¥µ¥Ý¡¼¥È¤·¤Æ¤¤¤ëÈó BSD ¥·¥¹¥Æ¥à
(System V ·Ï¤â´Þ¤à) ¤È¤Î´Ö¤Ç¤À¤¤¤¿¤¤°Ü¿¢À­¤¬¤¢¤ë¡£¤·¤«¤· System V ·Ï¤Ç¤Ï
¤¿¤¤¤¬¤¤ timeout ÊÑ¿ô¤ò exit ¤ÎÁ°¤Ë¥»¥Ã¥È¤¹¤ë¤¬¡¢
BSD ·Ï¤Ç¤Ï¤½¤¦¤Ç¤Ê¤¤¤Î¤ÇÃí°Õ¤¹¤ë¤³¤È¡£
.PP
.\"O .BR pselect ()
.\"O is defined in POSIX.1g, and in
.\"O POSIX.1-2001.
.BR pselect ()
¤Ï POSIX.1g ¤È POSIX.1-2001 ¤ÇÄêµÁ¤µ¤ì¤Æ¤¤¤ë¡£
.\"O .SH NOTES
.SH Ãí°Õ
.\"O An
.\"O .I fd_set
.\"O is a fixed size buffer.
.\"O Executing
.\"O .BR FD_CLR ()
.\"O or
.\"O .BR FD_SET ()
.\"O with a value of
.\"O .I fd
.\"O that is negative or is equal to or larger than
.\"O .B FD_SETSIZE
.\"O will result
.\"O in undefined behavior.
.\"O Moreover, POSIX requires
.\"O .I fd
.\"O to be a valid file descriptor.
.I fd_set
¤Ï¸ÇÄꥵ¥¤¥º¤Î¥Ð¥Ã¥Õ¥¡¤Ç¤¢¤ë¡£
Éé¤ä
.B FD_SETSIZE
°Ê¾å¤ÎÃͤò»ý¤Ä
.I fd
¤ËÂФ·¤Æ
.BR FD_CLR ()
¤ä
.BR FD_SET ()
¤ò¼Â¹Ô¤·¤¿¾ì¹ç¡¢
¤É¤Î¤è¤¦¤ÊÆ°ºî¤ò¤¹¤ë¤«¤ÏÄêµÁ¤µ¤ì¤Æ¤¤¤Ê¤¤¡£
¤Þ¤¿¡¢ POSIX ¤Ç¤Ï
.I fd
¤ÏÍ­¸ú¤Ê¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Ç¤Ê¤±¤ì¤Ð¤Ê¤é¤Ê¤¤¤Èµ¬Äꤵ¤ì¤Æ¤¤¤ë¡£

.\"O Concerning the types involved, the classical situation is that
.\"O the two fields of a
.\"O .I timeval
.\"O structure are typed as
.\"O .I long
.\"O (as shown above), and the structure is defined in
.\"O .IR <sys/time.h> .
·¿Àë¸À¤Ë´Ø¤·¤Æ¤Ï¡¢ÀΤʤ¬¤é¤Î¾õ¶·¤Ç¤Ï
.I timeval
¹½Â¤ÂΤΠ2 ¤Ä¤Î¥Õ¥£¡¼¥ë¥É¤Ï
(¾åµ­¤Î¤è¤¦¤Ë) ξÊý¤È¤â
.I long
·¿¤Ç¤¢¤ê¡¢¹½Â¤ÂΤÏ
.I <sys/time.h>
¤ÇÄêµÁ¤µ¤ì¤Æ¤¤¤ë¡£
.\"O The POSIX.1-2001 situation is
.\"O
.\"O .in +4n
.\"O .nf
.\"O struct timeval {
.\"O     time_t         tv_sec;     /* seconds */
.\"O     suseconds_t    tv_usec;    /* microseconds */
.\"O };
.\"O .fi
.\"O .in
.\"O
.\"O where the structure is defined in
.\"O .I <sys/select.h>
.\"O and the data types
.\"O .I time_t
.\"O and
.\"O .I suseconds_t
.\"O are defined in
.\"O .IR <sys/types.h> .
POSIX.1-2001 ¤Î²¼¤Ç¤Ï¡¢°Ê²¼¤Î¤è¤¦¤Ë¤Ê¤Ã¤Æ¤¤¤ë¡£

.in +4n
.nf
struct timeval {
         time_t         tv_sec;     /* ÉÃ */
         suseconds_t    tv_usec;    /* ¥Þ¥¤¥¯¥íÉà */
};
.fi
.in

¤³¤Î¹½Â¤ÂΤÏ
.I <sys/select.h>
¤ÇÄêµÁ¤µ¤ì¤Æ¤ª¤ê¡¢¥Ç¡¼¥¿·¿
.I time_t
¤È
.I suseconds_t
¤Ï
.I <sys/types.h>
¤ÇÄêµÁ¤µ¤ì¤Æ¤¤¤ë¡£
.LP
.\"O Concerning prototypes, the classical situation is that one should
.\"O include
.\"O .I <time.h>
.\"O for
.\"O .BR select ().
¥×¥í¥È¥¿¥¤¥×¤Ë´Ø¤·¤Æ¤Ï¡¢ÀΤʤ¬¤é¤Î¾õ¶·¤Ç
.BR select ()
¤ò»È¤¤¤¿¤¤¾ì¹ç¤Ï¡¢
.I <time.h>
¤ò¥¤¥ó¥¯¥ë¡¼¥É¤¹¤ì¤Ð¤è¤¤¡£
.\"O The POSIX.1-2001 situation is that one should include
.\"O .I <sys/select.h>
.\"O for
.\"O .BR select ()
.\"O and
.\"O .BR pselect ().
POSIX.1-2001 ¤Î´Ä¶­¤Ç
.BR select ()
¤È
.BR pselect ()
¤ò»È¤¤¤¿¤¤¾ì¹ç¤Ï¡¢
.I <sys/select.h>
¤ò¥¤¥ó¥¯¥ë¡¼¥É¤¹¤ì¤Ð¤è¤¤¡£

.\"O Libc4 and libc5 do not have a
.\"O .I <sys/select.h>
.\"O header; under glibc 2.0 and later this header exists.
¥Ø¥Ã¥À¥Õ¥¡¥¤¥ë
.I <sys/select.h>
¤Ï libc4 ¤È libc5 ¤Ë¤Ï¤Ê¤¯¡¢glibc 2.0 °Ê¹ß¤Ë¸ºß¤¹¤ë¡£
.\"O Under glibc 2.0 it unconditionally gives the wrong prototype for
.\"O .BR pselect ().
.\"O Under glibc 2.1 to 2.2.1 it gives
.\"O .BR pselect ()
.\"O when
.\"O .B _GNU_SOURCE
.\"O is defined.
.\"O Since glibc 2.2.2 the requirements are as shown in the SYNOPSIS.
°­¤¤¤³¤È¤Ë glibc 2.0 °ÊÁ°¤Ç¤Ï
.BR pselect ()
¤Î¥×¥í¥È¥¿¥¤¥×¤¬´Ö°ã¤Ã¤Æ¤¤¤ë¡£
glibc 2.1 ¤«¤é 2.2.1 ¤Ç¤Ï
.B _GNU_SOURCE
¤¬ÄêµÁ¤µ¤ì¤Æ¤¤¤ë¾ì¹ç¤Ë¡¢
.BR pselect ()
¤¬Ä󶡤µ¤ì¤ë¡£
glibc 2.2.2 °Ê¹ß¤Ç¤Ï¡¢
.BR pselect ()
¤ò»ÈÍѤ¹¤ë¤Ë¤Ï¡¢¡Ö½ñ¼°¡×¤Ëµ­ºÜ¤µ¤ì¤¿Í×·ï¤òËþ¤¿¤¹É¬Íפ¬¤¢¤ë¡£
.\"O .SS "LINUX NOTES"
.SS "Linux ¤Ç¤ÎÃí°Õ"
.\"O The Linux
.\"O .BR pselect ()
.\"O system call modifies its
.\"O .I timeout
.\"O argument.
Linux ¤Î
.BR pselect ()
¥·¥¹¥Æ¥à¥³¡¼¥ë¤Ï
.I timeout
°ú¤­¿ô¤òÊѹ¹¤¹¤ë¡£
.\"O However, the glibc wrapper function hides this behavior
.\"O by using a local variable for the timeout argument that
.\"O is passed to the system call.
.\"O Thus, the glibc
.\"O .BR pselect ()
.\"O function does not modify its timeout argument;
.\"O this is the behavior required by POSIX.1-2001.
¤·¤«¤·¡¢ glibc ¤Î¥é¥Ã¥Ñ¡¼´Ø¿ô¤Ï¡¢¥·¥¹¥Æ¥à¥³¡¼¥ë¤ËÅϤ¹ timeout °ú¤­¿ô
¤È¤·¤Æ¥í¡¼¥«¥ëÊÑ¿ô¤ò»È¤¦¤³¤È¤Ç¤³¤ÎÆ°ºî¤ò±£Ê䷤Ƥ¤¤ë¡£
¤³¤Î¤¿¤á¡¢glibc ¤Î
.BR pselect ()
´Ø¿ô¤Ï timeout °ú¤­¿ô¤òÊѹ¹¤·¤Ê¤¤¡£
¤³¤ì¤¬ POSIX.1-2001 ¤¬Í׵ᤷ¤Æ¤¤¤ëÆ°ºî¤Ç¤¢¤ë¡£
.\"O .SH BUGS
.SH ¥Ð¥°
.\"O Glibc 2.0 provided a version of
.\"O .BR pselect ()
.\"O that did not take a
.\"O .I sigmask
.\"O argument.
glibc 2.0 ¤Ç¤Ï¡¢
.I sigmask
°ú¤­¿ô¤ò¼è¤é¤Ê¤¤¥Ð¡¼¥¸¥ç¥ó¤Î
.BR pselect ()
¤¬Ä󶡤µ¤ì¤Æ¤¤¤¿¡£

.\"O Since version 2.1, glibc has provided an emulation of
.\"O .BR pselect ()
.\"O that is implemented using
.\"O .BR sigprocmask (2)
.\"O and
.\"O .BR select ().
.\"O This implementation remains vulnerable to the very race condition that
.\"O .BR pselect ()
.\"O was designed to prevent.
¥Ð¡¼¥¸¥ç¥ó 2.1 °Ê¹ß¤Î glibc ¤Ç¤Ï¡¢
.BR pselect ()
¤Ï
.BR sigprocmask (2)
¤È
.BR select ()
¤ò»È¤Ã¤Æ¥¨¥ß¥å¥ì¡¼¥È¤µ¤ì¤Æ¤¤¤¿¡£
¤³¤Î¼ÂÁõ¤Ë¤Ï¤­¤ï¤É¤¤¶¥¹ç¾ò·ï¤Ë¤ª¤¤¤ÆÀȼåÀ­¤¬»Ä¤Ã¤Æ¤¤¤ë¡£
¤³¤Î¶¥¹ç¾ò·ï¤Ë¤ª¤±¤ëÌäÂê¤òËɻߤ¹¤ë¤¿¤á¤Ë
.BR pselect ()
¤ÏÀ߷פµ¤ì¤¿¤Î¤Ç¤¢¤ë¡£
.\"O On systems that lack
.\"O .BR pselect (),
.\"O reliable (and more portable) signal trapping can be achieved
.\"O using the self-pipe trick
.\"O (where a signal handler writes a byte to a pipe whose other end
.\"O is monitored by
.\"O .BR select ()
.\"O in the main program.)
.BR pselect ()
¤¬¤Ê¤¤¥·¥¹¥Æ¥à¤Ë¤ª¤¤¤Æ¡¢
¥·¥°¥Ê¥ë¤ÎÊ᪤ò¿®ÍêÀ­¤¬¤¢¤ê (°Ü¿¢À­¤â¹â¤¤) ÊýË¡¤Ç¹Ô¤¦¤Ë¤Ï¡¢
¼«¸Ê¥Ñ¥¤¥× (self-pipe) ¤È¤¤¤¦µ»¤ò»È¤¦¤È¤è¤¤ (¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ï¥Ñ¥¤¥×¤Ø
1 ¥Ð¥¤¥È¤Î¥Ç¡¼¥¿¤ò½ñ¤­¹þ¤ß¡¢Æ±¤¸¥Ñ¥¤¥×¤Î¤â¤¦°ìü¤ò¥á¥¤¥ó¥×¥í¥°¥é¥à¤Î
.BR select ()
¤Ç´Æ»ë¤¹¤ë¤È¤¤¤¦ÊýË¡¤Ç¤¢¤ë)¡£

.\"O Under Linux,
.\"O .BR select ()
.\"O may report a socket file descriptor as "ready for reading", while
.\"O nevertheless a subsequent read blocks.
.\"O This could for example
.\"O happen when data has arrived but upon examination has wrong
.\"O checksum and is discarded.
.\"O There may be other circumstances
.\"O in which a file descriptor is spuriously reported as ready.
.\"O .\" Stevens discusses a case where accept can block after select
.\"O .\" returns successfully because of an intervening RST from the client.
.\"O Thus it may be safer to use
.\"O .B O_NONBLOCK
.\"O on sockets that should not block.
Linux ¤Ç¤Ï¡¢
.BR select ()
¤¬¥½¥±¥Ã¥È¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Ç "Æɤ߹þ¤ß¤Î½àÈ÷¤¬¤Ç¤­¤¿" ¤ÈÊó¹ð¤·¤¿¾ì¹ç¤Ç¤â¡¢
¤³¤Î¸å¤Ç read ¤ò¹Ô¤¦¤ÈÄä»ß (block) ¤¹¤ë¤³¤È¤¬¤¢¤ë¡£¤³¤Î¤è¤¦¤Ê¾õ¶·¤Ï¡¢
Î㤨¤Ð¡¢¥Ç¡¼¥¿¤¬ÅþÃ夷¤¿¤¬¡¢¸¡ºº¤Ç¥Á¥§¥Ã¥¯¥µ¥à°Û¾ï¤¬¸«¤Ä¤«¤êÇÑ´þ¤µ¤ì¤¿»þ
¤Ê¤É¤Ëµ¯¤³¤ê¤¨¤ë¡£Â¾¤Ë¤â¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤¬½àÈ÷¤Ç¤­¤¿¤È´Ö°ã¤Ã¤Æ
Êó¹ð¤µ¤ì¤ë¾õ¶·¤¬µ¯¤³¤ë¤«¤â¤·¤ì¤Ê¤¤¡£
.\" Stevens ¤¬µó¤²¤¿¤Î¤Ï¡¢select ¤¬À®¸ù¤·¤ÆÉüµ¢¤·¤Æ¤«¤é accept ¤¬
.\" ¸Æ¤Ð¤ì¤ë¤Þ¤Ç¤Î´Ö¤Ë¡¢¥¯¥é¥¤¥¢¥ó¥È¤«¤é RST ¤¬Á÷¤é¤ì¤ë¤È¡¢
.\" accept ¤¬Ää»ß¤¹¤ë¾ì¹ç¤Ç¤¢¤ë¡£
¤·¤¿¤¬¤Ã¤Æ¡¢Ää»ß¤¹¤Ù¤­¤Ç¤Ï¤Ê¤¤¥½¥±¥Ã¥È¤ËÂФ·¤Æ¤Ï
.B O_NONBLOCK
¤ò»È¤¦¤È¤è¤ê°ÂÁ´¤Ç¤¢¤í¤¦¡£
.\"O .\" Maybe the kernel should have returned EIO in such a situation?
.\" ¿ʬ¡¢¤³¤Î¤è¤¦¤Ê¾õ¶·¤Ç¤Ï¥«¡¼¥Í¥ë¤Ï EIO ¤òÊÖ¤·¤Æ¤·¤Þ¤¦?

.\"O On Linux,
.\"O .BR select ()
.\"O also modifies
.\"O .I timeout
.\"O if the call is interrupted by a signal handler (i.e., the
.\"O .B EINTR
.\"O error return).
.\"O This is not permitted by POSIX.1-2001.
.\"O The Linux
.\"O .BR pselect ()
.\"O system call has the same behavior,
.\"O but the glibc wrapper hides this behavior by internally copying the
.\"O .I timeout
.\"O to a local variable and passing that variable to the system call.
Linux ¤Ç¤Ï¡¢
.BR select ()
¤¬¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ë¤è¤ê³ä¤ê¹þ¤Þ¤ì¤¿¾ì¹ç (¤Ä¤Þ¤ê
.B EINTR
¥¨¥é¡¼¤¬ÊÖ¤ë¾ì¹ç)¡¢
.I timeout
¤âÊѹ¹¤¹¤ë¡£
¤³¤ì¤Ï POSIX.1-2001 ¤Ç¤Ïǧ¤á¤é¤ì¤Æ¤¤¤Ê¤¤µóÆ°¤Ç¤¢¤ë¡£
Linux ¤Î
.BR pselect ()
¥·¥¹¥Æ¥à¥³¡¼¥ë¤âƱ¤¸µóÆ°¤ò¤¹¤ë¤¬¡¢
glibc ¤Î¥é¥Ã¥Ñ¡¼´Ø¿ô¤¬¤³¤ÎµóÆ°¤ò±£Ê䷤Ƥ¤¤ë¡£
¶ñÂÎŪ¤Ë¤Ï¡¢glibc ¤Î¥é¥Ã¥Ñ¡¼´Ø¿ô¤ÎÆâÉô¤Ç¡¢
.I timeout
¤ò¥í¡¼¥«¥ëÊÑ¿ô¤Ë¥³¥Ô¡¼¤·¡¢
¤³¤Î¥í¡¼¥«¥ëÊÑ¿ô¤ò¥·¥¹¥Æ¥à¥³¡¼¥ë¤ËÅϤ·¤Æ¤¤¤ë¡£
.\"O .SH EXAMPLE
.SH Îã
.nf
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

.\"O int
.\"O main(void)
.\"O {
.\"O     fd_set rfds;
.\"O     struct timeval tv;
.\"O     int retval;
.\"O
.\"O     /* Watch stdin (fd 0) to see when it has input. */
.\"O     FD_ZERO(&rfds);
.\"O     FD_SET(0, &rfds);
.\"O
.\"O     /* Wait up to five seconds. */
.\"O     tv.tv_sec = 5;
.\"O     tv.tv_usec = 0;
.\"O
.\"O     retval = select(1, &rfds, NULL, NULL, &tv);
.\"O     /* Don't rely on the value of tv now! */
.\"O
.\"O     if (retval == \-1)
.\"O         perror("select()");
.\"O     else if (retval)
.\"O         printf("Data is available now.\\n");
.\"O         /* FD_ISSET(0, &rfds) will be true. */
.\"O     else
.\"O         printf("No data within five seconds.\\n");
.\"O
.\"O     exit(EXIT_SUCCESS);
.\"O }
int
main(void)
{
    fd_set rfds;
    struct timeval tv;
    int retval;

    /* stdin (fd 0) ¤ò´Æ»ë¤·¡¢ÆþÎϤ¬¤¢¤Ã¤¿¾ì¹ç¤Ëɽ¼¨¤¹¤ë¡£*/
    FD_ZERO(&rfds);
    FD_SET(0, &rfds);

    /* 5 Éôִƻ뤹¤ë¡£*/
    tv.tv_sec = 5;
    tv.tv_usec = 0;

    retval = select(1, &rfds, NULL, NULL, &tv);
    /* ¤³¤Î»þÅÀ¤Ç¤Î tv ¤ÎÃͤò¿®Íꤷ¤Æ¤Ï¤Ê¤é¤Ê¤¤¡£*/

    if (retval == \-1)
        perror("select()");
    else if (retval)
        printf("º£¡¢¥Ç¡¼¥¿¤¬¼èÆÀ¤Ç¤­¤Þ¤·¤¿¡£\\n");
        /* FD_ISSET(0, &rfds) ¤¬ true ¤Ë¤Ê¤ë¡£*/
    else
        printf("5 ÉðÊÆâ¤Ë¥Ç¡¼¥¿¤¬ÆþÎϤµ¤ì¤Þ¤»¤ó¤Ç¤·¤¿¡£\\n");

    exit(EXIT_SUCCESS);
}
.fi
.\"O .SH "SEE ALSO"
.SH ´ØÏ¢¹àÌÜ
.\"O For a tutorial with discussion and examples, see
.\"O .BR select_tut (2).
¹Í»¡¤È»ÈÍÑÎã¤Î½ñ¤«¤ì¤¿¥Á¥å¡¼¥È¥ê¥¢¥ë¤È¤·¤Æ¡¢
.BR select_tut (2)
¤¬¤¢¤ë¡£
.LP
.\"O For vaguely related stuff, see
´Ø·¸¤¬¤¢¤ê¤½¤¦¤Ê¤â¤Î¤òµó¤²¤Æ¤ª¤¯:
.BR accept (2),
.BR connect (2),
.BR poll (2),
.BR read (2),
.BR recv (2),
.BR send (2),
.BR sigprocmask (2),
.BR write (2),
.BR epoll (7),
.BR time (7)