133 lines
3.6 KiB
Groff
133 lines
3.6 KiB
Groff
.\" $OpenBSD: sem_wait.3,v 1.10 2018/04/24 16:28:42 pirofti Exp $
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.\"
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.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD: src/lib/libc_r/man/sem_wait.3,v 1.8 2001/10/01 16:09:09 ru Exp $
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.Dd $Mdocdate: April 24 2018 $
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.Dt SEM_WAIT 3
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.Os
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.Sh NAME
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.Nm sem_wait ,
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.Nm sem_timedwait ,
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.Nm sem_trywait
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.Nd decrement (lock) a semaphore
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.Sh SYNOPSIS
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.In semaphore.h
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.Ft int
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.Fn sem_wait "sem_t *sem"
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.Ft int
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.Fn sem_timedwait "sem_t *sem" "const struct timespec *abstime"
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.Ft int
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.Fn sem_trywait "sem_t *sem"
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.Sh DESCRIPTION
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The
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.Fn sem_wait
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function decrements (locks) the semaphore pointed to by
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.Fa sem ,
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but blocks if the value of
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.Fa sem
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is zero, until the value is non-zero and the value can be decremented.
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.Pp
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The
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.Fn sem_timedwait
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function decrements (locks) the semaphore pointed to by
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.Fa sem ,
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but blocks if the value of
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.Fa sem
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is zero, until either the value is non-zero and can be decremented
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or the system time specified by
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.Fa abstime
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is reached.
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.Pp
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The
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.Fn sem_trywait
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function decrements (locks) the semaphore pointed to by
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.Fa sem
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only if the value is non-zero.
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Otherwise, the semaphore is not decremented and
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an error is returned.
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.Sh RETURN VALUES
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.Rv -std sem_wait sem_timedwait sem_trywait
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.Sh ERRORS
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.Fn sem_wait ,
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.Fn sem_timedwait ,
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and
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.Fn sem_trywait
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Fa sem
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points to an invalid semaphore.
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.El
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.Pp
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Additionally,
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.Fn sem_wait
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and
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.Fn sem_timedwait
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINTR
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The call was interrupted by a signal.
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.El
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.Pp
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Additionally,
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.Fn sem_timedwait
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Fa abstime
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was
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.Dv NULL
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or specified a nanosecond value less than zero or greater than 1000 million.
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.It Bq Er ETIMEDOUT
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The semaphore value was zero and could not be decremented before
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.Fa abstime
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was reached.
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.El
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.Pp
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Additionally,
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.Fn sem_trywait
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The semaphore value was zero, and thus could not be decremented.
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.El
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.Sh SEE ALSO
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.Xr sem_destroy 3 ,
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.Xr sem_getvalue 3 ,
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.Xr sem_init 3 ,
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.Xr sem_open 3 ,
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.Xr sem_post 3
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.Sh STANDARDS
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.Fn sem_wait ,
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.Fn sem_timedwait ,
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and
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.Fn sem_trywait
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conform to
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.St -p1003.1-2008 .
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