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.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.\" Japanese Version Copyright (c) 2006 Akihiro MOTOKI all rights reserved.
.\" Translated 2006-04-18, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\"
.TH SEM_WAIT 3 2010-02-25 "Linux" "Linux Programmer's Manual"
.\"O .SH NAME
.SH ̾Á°
.\"O sem_wait, sem_timedwait, sem_trywait \- lock a semaphore
sem_wait, sem_timedwait, sem_trywait \- ¥»¥Þ¥Õ¥©¤ò¥í¥Ã¥¯¤¹¤ë
.\"O .SH SYNOPSIS
.SH ½ñ¼°
.nf
.B #include <semaphore.h>
.sp
.BI "int sem_wait(sem_t *" sem );
.sp
.BI "int sem_trywait(sem_t *" sem );
.sp
.BI "int sem_timedwait(sem_t *" sem ", const struct timespec *" abs_timeout );
.fi
.sp
.sp
.\"O Link with \fI\-lrt\fP or \fI\-pthread\fP.
\fI\-lrt\fP ¤Þ¤¿¤Ï \fI\-pthread\fP ¤Ç¥ê¥ó¥¯¤¹¤ë¡£
.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 sem_timedwait ():
_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O .BR sem_wait ()
.\"O decrements (locks) the semaphore pointed to by
.\"O .IR sem .
.\"O If the semaphore's value is greater than zero,
.\"O then the decrement proceeds, and the function returns, immediately.
.\"O If the semaphore currently has the value zero,
.\"O then the call blocks until either it becomes possible to perform
.\"O the decrement (i.e., the semaphore value rises above zero),
.\"O or a signal handler interrupts the call.
.BR sem_wait ()
¤Ï
.I sem
¤¬»Ø¤¹¥»¥Þ¥Õ¥©¤ÎÃͤò 1 ¸º¤é¤¹ (¥í¥Ã¥¯¤¹¤ë)¡£
¥»¥Þ¥Õ¥©¤ÎÃͤ¬ 0 ¤è¤êÂ礭¤¤¾ì¹ç¡¢¸º»»¤¬¼Â¹Ô¤µ¤ì¡¢´Ø¿ô¤Ïľ¤Á¤ËÉüµ¢¤¹¤ë¡£
¥»¥Þ¥Õ¥©¤Î¸½ºßÃͤ¬ 0 ¤Î¾ì¹ç¤Ë¤Ï¡¢¸º»»¤ò¼Â¹Ô¤Ç¤­¤ë¤è¤¦¤Ë¤Ê¤ë
(¤Ä¤Þ¤ê¡¢¥»¥Þ¥Õ¥©¤ÎÃͤ¬ 0 ¤è¤êÂ礭¤ÊÃͤˤʤë) ¤Þ¤Ç¡¢¤â¤·¤¯¤Ï
¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ë¤è¤Ã¤Æ¸Æ¤Ó½Ð¤·¤¬ÃæÃǤµ¤ì¤ë¤Þ¤Ç¡¢
´Ø¿ô¸Æ¤Ó½Ð¤·¤ÏÄä»ß (block) ¤¹¤ë¡£

.\"O .BR sem_trywait ()
.\"O is the same as
.\"O .BR sem_wait (),
.\"O except that if the decrement cannot be immediately performed,
.\"O then call returns an error
.\"O .RI ( errno
.\"O set to
.\"O .BR EAGAIN )
.\"O instead of blocking.
.BR sem_trywait ()
¤Ï
.BR sem_wait ()
¤ÈƱ¤¸¤À¤¬¡¢¥»¥Þ¥Õ¥©Ãͤθº»»¤ò¤¹¤°¤Ë¼Â¹Ô¤Ç¤­¤Ê¤«¤Ã¤¿¾ì¹ç¤Ë¡¢
Ää»ß (block) ¤¹¤ë¤Î¤Ç¤Ï¤Ê¤¯¥¨¥é¡¼¤ÇÉüµ¢¤¹¤ë
.RI ( errno
¤Ë
.B EAGAIN
¤¬¥»¥Ã¥È¤µ¤ì¤ë) ÅÀ¤¬°Û¤Ê¤ë¡£

.\"O .BR sem_timedwait ()
.\"O is the same as
.\"O .BR sem_wait (),
.\"O except that
.\"O .I abs_timeout
.\"O specifies a limit on the amount of time that the call
.\"O should block if the decrement cannot be immediately performed.
.\"O The
.\"O .I abs_timeout
.\"O argument points to a structure that specifies an absolute timeout
.\"O in seconds and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
.\"O This structure is defined as follows:
.BR sem_timedwait ()
¤Ï
.BR sem_wait ()
¤ÈƱ¤¸¤À¤¬¡¢¥»¥Þ¥Õ¥©Ãͤθº»»¤ò¤¹¤°¤Ë¼Â¹Ô¤Ç¤­¤Ê¤«¤Ã¤¿¾ì¹ç¤Ë
´Ø¿ô¸Æ¤Ó½Ð¤·¤¬Ää»ß¤¹¤ë»þ´Ö¤Î¾å¸Â¤ò
.I abs_timeout
¤Ç»ØÄꤹ¤ëÅÀ¤¬°Û¤Ê¤ë¡£
.I abs_timeout
°ú¤­¿ô¤Ï¡¢¥¿¥¤¥à¥¢¥¦¥È»þ¹ï¤ò»ØÄꤹ¤ë¹½Â¤ÂΤؤΥݥ¤¥ó¥¿¤Ç¤¢¤ë¡£
¤³¤Î¹½Â¤ÂΤˤϡ¢¥¿¥¤¥à¥¢¥¦¥È»þ¹ï¤ò»þ¹ïµª¸µ (Epoch;
1970-01-01 00:00:00 +0000 (UTC)) ¤«¤é¤Î
·Ð²á»þ´Ö (ÉáܥʥÎÉÃ) ¤Ç»ØÄꤹ¤ë¡£
¹½Â¤ÂΤϰʲ¼¤Î¤è¤¦¤ËÄêµÁ¤µ¤ì¤Æ¤¤¤ë:

.nf
.in +4n
struct timespec {
    time_t tv_sec;      /* Seconds */
    long   tv_nsec;     /* Nanoseconds [0 .. 999999999] */
};
.in
.fi
.PP
.\"O If the timeout has already expired by the time of the call,
.\"O and the semaphore could not be locked immediately,
.\"O then
.\"O .BR sem_timedwait ()
.\"O fails with a timeout error
.\"O .RI ( errno
.\"O set to
.\"O .BR ETIMEDOUT ).
´Ø¿ô¸Æ¤Ó½Ð¤·»þÅÀ¤Ç¤¹¤Ç¤Ë¥¿¥¤¥à¥¢¥¦¥È¤Ë»ØÄꤷ¤¿»þ¹ï¤¬²á¤®¤Æ¤ª¤ê¡¢
¤«¤Ä¥»¥Þ¥Õ¥©¤ò¤¹¤°¤Ë¥í¥Ã¥¯¤Ç¤­¤Ê¤«¤Ã¤¿¾ì¹ç¤Ï¡¢
.BR sem_timedwait ()
¤Ï¥¿¥¤¥à¥¢¥¦¥È¥¨¥é¡¼
.RI ( errno
¤Ë
.B ETIMEDOUT
¤¬¥»¥Ã¥È¤µ¤ì¤ë) ¤Ç¼ºÇÔ¤¹¤ë¡£

.\"O If the operation can be performed immediately, then
.\"O .BR sem_timedwait ()
.\"O never fails with a timeout error, regardless of the value of
.\"O .IR abs_timeout .
.\"O Furthermore, the validity of
.\"O .I abs_timeout
.\"O is not checked in this case.
¥»¥Þ¥Õ¥©Áàºî¤¬¤¹¤°¤Ë¼Â¹Ô¤Ç¤­¤ë¤È¤­¤Ï¡¢
.I abs_timeout
¤¬¤É¤ó¤ÊÃͤǤ¢¤Ã¤Æ¤â
.BR sem_timedwait ()
¤¬¼ºÇÔ¤¹¤ë¤³¤È¤Ï·è¤·¤Æ¤Ê¤¤¡£¤µ¤é¤Ë¤¤¤¦¤È¡¢¤³¤Î¾ì¹ç¤Ë¤Ï
.I abs_timeout
¤ÎÀµÅöÀ­¤Î¸¡ºº¤Ï¹Ô¤ï¤ì¤Ê¤¤¡£
.\"O .SH RETURN VALUE
.SH ÊÖ¤êÃÍ
.\"O All of these functions return 0 on success;
.\"O on error, the value of the semaphore is left unchanged,
.\"O \-1 is returned, and
.\"O .I errno
.\"O is set to indicate the error.
À®¸ù¤¹¤ë¤È¡¢¤³¤ì¤é¤Î´Ø¿ô¤Ï 0 ¤òÊÖ¤¹¡£
¥¨¥é¡¼¤Î¾ì¹ç¡¢¥»¥Þ¥Õ¥©¤ÎÃͤòÊѹ¹¤»¤º¤Ë¡¢\-1 ¤òÊÖ¤·¡¢
.I errno
¤Ë¥¨¥é¡¼¤ò¼¨¤¹Ãͤò¥»¥Ã¥È¤¹¤ë¡£
.\"O .SH ERRORS
.SH ¥¨¥é¡¼
.TP
.B EINTR
.\"O The call was interrupted by a signal handler; see
.\"O .BR signal (7).
¸Æ¤Ó½Ð¤·¤Ï¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ë¤è¤êÃæÃǤµ¤ì¤¿¡£
.BR signal (7)
»²¾È¡£
.TP
.B EINVAL
.\"O .I sem
.\"O is not a valid semaphore.
.I sem
¤ÏÍ­¸ú¤Ê¥»¥Þ¥Õ¥©¤Ç¤Ê¤¤¡£
.PP
.\"O The following additional error can occur for
.\"O .BR sem_trywait ():
.BR sem_trywait ()
¤Î¾ì¹ç¤Ë¤Ï¡¢¾åµ­¤Ë²Ã¤¨¤Æ°Ê²¼¤Î¥¨¥é¡¼¤âµ¯¤³¤ë¡£
.TP
.B EAGAIN
.\"O The operation could not be performed without blocking (i.e., the
.\"O semaphore currently has the value zero).
Ää»ß (block) ¤»¤º¤Ë¥í¥Ã¥¯Áàºî¤ò´°Î»¤Ç¤­¤Ê¤«¤Ã¤¿ (¤Ä¤Þ¤ê¡¢
¥»¥Þ¥Õ¥©¤Î¸½ºß¤ÎÃͤ¬ 0 ¤Ç¤¢¤Ã¤¿)¡£
.PP
.\"O The following additional errors can occur for
.\"O .BR sem_timedwait ():
.BR sem_timedwait ()
¤Î¾ì¹ç¡¢°Ê²¼¤Î¥¨¥é¡¼¤âµ¯¤³¤ë¡£
.TP
.B EINVAL
.\"O The value of
.\"O .I abs_timeout.tv_nsecs
.\"O is less than 0, or greater than or equal to 1000 million.
.I abs_timeout.tv_nsecs
¤ÎÃͤ¬ 0 ̤Ëþ¡¢¤â¤·¤¯¤Ï 1,000,000,000 °Ê¾å¤Ç¤¢¤ë¡£
.TP
.B ETIMEDOUT
.\"O The call timed out before the semaphore could be locked.
¥»¥Þ¥Õ¥©¤Î¥í¥Ã¥¯¤ËÀ®¸ù¤¹¤ëÁ°¤Ë»þ´ÖÀÚ¤ì¤È¤Ê¤Ã¤¿¡£
.\"O .\" POSIX.1-2001 also allows EDEADLK -- "A deadlock condition
.\"O .\" was detected", but this does not occur on Linux(?).
.\" POSIX.1-2001 ¤Ç¤Ï¥¨¥é¡¼¤È¤·¤Æ EDEADLK ¤âÍÑ°Õ¤·¤Æ¤¤¤ë¡£
.\" ¤³¤ì¤Ï¥Ç¥Ã¥É¥í¥Ã¥¯¾ò·ï¤ò¸¡½Ð¤·¤¿¤³¤È¤ò¼¨¤¹¤â¤Î¤À¤¬¡¢
.\" Linux ¤ÇȯÀ¸¤¹¤ë¤³¤È¤Ï¤Ê¤¤(?)
.\"O .SH CONFORMING TO
POSIX.1-2001.
.\"O .SH NOTES
.SH Ãí°Õ
.\"O A signal handler always interrupts a blocked call to
.\"O one of these functions, regardless of the use of the
.\"O .BR sigaction (2)
.\"O .B SA_RESTART
.\"O flag.
¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ï¡¢
.BR sigaction (2)
¤Î
.B SA_RESTART
¥Õ¥é¥°¤ò»ÈÍѤ·¤Æ¤¤¤ë¤«¤É¤¦¤«¤Ë´Ø¤ï¤é¤º¡¢¤³¤ì¤é¤Î´Ø¿ô¤Î¸Æ¤Ó½Ð¤·¤¬
Ää»ß¤·¤Æ¤¤¤ë¾ì¹ç¡¢¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ë¤è¤ê¾ï¤ËÃæÃǤµ¤ì¤ë¡£
.\"O .\" sem_wait() is always interrupted on most other implementations,
.\"O .\" but on FreeBSD 5.4 SA_RESTART does cause restarting.
.\" sem_wait() ¤Ï¾¤Î¤Û¤È¤ó¤É¤Î¼ÂÁõ¤Ç¤Ï¾ï¤ËÃæÃǤµ¤ì¤ë¤¬¡¢
.\" FreeBSD 5.4 ¤Ç¤Ï SA_RESTART ¤ò»ØÄꤷ¤Æ¤ª¤¯¤È¼Â¹Ô¤¬ºÆ³«¤µ¤ì¤ë¡£
.\"O .SH EXAMPLE
.SH Îã
.PP
.\"O The (somewhat trivial) program shown below operates on an
.\"O unnamed semaphore.
.\"O The program expects two command-line arguments.
.\"O The first argument specifies a seconds value that is used to
.\"O set an alarm timer to generate a
.\"O .B SIGALRM
.\"O signal.
.\"O This handler performs a
.\"O .BR sem_post (3)
.\"O to increment the semaphore that is being waited on in
.\"O .I main()
.\"O using
.\"O .BR sem_timedwait ().
.\"O The second command-line argument specifies the length
.\"O of the timeout, in seconds, for
.\"O .BR sem_timedwait ().
.\"O The following shows what happens on two different runs of the program:
°Ê²¼¤Ë¼¨¤¹ (¤Á¤ç¤Ã¤È¤·¤¿) ¥×¥í¥°¥é¥à¤Ï̾Á°¤Ê¤·¥»¥Þ¥Õ¥©¤ÎÁàºî¤ò¹Ô¤¦¡£
¥×¥í¥°¥é¥à¤Ï¥³¥Þ¥ó¥É¥é¥¤¥ó°ú¤­¿ô¤ò 2 ¤Ä¼è¤ë¡£
ºÇ½é¤Î°ú¤­¿ô¤Ë¤Ï¡¢
.B SIGALRM
¥·¥°¥Ê¥ë¤òÀ¸À®¤¹¤ë¤¿¤á¤Î¥¢¥é¡¼¥à¥¿¥¤¥Þ¡¼¤ÎÀßÄê¤Ë»È¤ï¤ì¤ëÃͤò
ÉÃñ°Ì¤Ç»ØÄꤹ¤ë¡£¤³¤Î¥·¥°¥Ê¥ë¥Ï¥ó¥É¥é¤Ï¡¢
.I main()
Æâ¤Ç
.BR sem_timedwait ()
¤ò»È¤Ã¤ÆÂԤäƤ¤¤ë¥»¥Þ¥Õ¥©¤ò¡¢
.BR sem_post (3)
¤ò»È¤Ã¤Æ²Ã»»¤¹¤ë¡£
2ÈÖÌܤΰú¤­¿ô¤Ë¤Ï¡¢
.BR sem_timedwait ()
¤ËÅϤ¹¥¿¥¤¥à¥¢¥¦¥È¤Þ¤Ç¤Î»þ´Ö¤òÉÃñ°Ì¤Ç»ØÄꤹ¤ë¡£

.in +4n
.nf
.RB "$" " ./a.out 2 3"
About to call sem_timedwait()
sem_post() from handler
sem_getvalue() from handler; value = 1
sem_timedwait() succeeded
.RB "$" " ./a.out 2 1"
About to call sem_timedwait()
sem_timedwait() timed out
.fi
.in
.\"O .SS Program source
.SS ¥×¥í¥°¥é¥à¤Î¥½¡¼¥¹
\&
.nf
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <time.h>
#include <assert.h>
#include <errno.h>
#include <signal.h>

sem_t sem;

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

static void
handler(int sig)
{
    write(STDOUT_FILENO, "sem_post() from handler\\n", 24);
    if (sem_post(&sem) == \-1) {
        write(STDERR_FILENO, "sem_post() failed\\n", 18);
        _exit(EXIT_FAILURE);
    }
}

int
main(int argc, char *argv[])
{
    struct sigaction sa;
    struct timespec ts;
    int s;

    if (argc != 3) {
        fprintf(stderr, "Usage: %s <alarm\-secs> <wait\-secs>\\n",
                argv[0]);
        exit(EXIT_FAILURE);
    }

    if (sem_init(&sem, 0, 0) == \-1)
        handle_error("sem_init");

    /* Establish SIGALRM handler; set alarm timer using argv[1] */

    sa.sa_handler = handler;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    if (sigaction(SIGALRM, &sa, NULL) == \-1)
        handle_error("sigaction");

    alarm(atoi(argv[1]));

    /* Calculate relative interval as current time plus
       number of seconds given argv[2] */

    if (clock_gettime(CLOCK_REALTIME, &ts) == \-1)
        handle_error("clock_gettime");

    ts.tv_sec += atoi(argv[2]);

    printf("main() about to call sem_timedwait()\\n");
    while ((s = sem_timedwait(&sem, &ts)) == \-1 && errno == EINTR)
        continue;       /* Restart if interrupted by handler */

    /* Check what happened */

    if (s == \-1) {
        if (errno == ETIMEDOUT)
            printf("sem_timedwait() timed out\\n");
        else
            perror("sem_timedwait");
    } else
        printf("sem_timedwait() succeeded\\n");

    exit((s == 0) ? EXIT_SUCCESS : EXIT_FAILURE);
}
.fi
.\"O .SH "SEE ALSO"
.SH ´ØÏ¢¹àÌÜ
.BR clock_gettime (2),
.BR sem_getvalue (3),
.BR sem_post (3),
.BR sem_overview (7),
.BR time (7)