2000-07-18 01:38:19 +00:00
|
|
|
.\" Copyright (C) 2000 Jason Evans <jasone@freebsd.org>.
|
2000-02-16 19:31:53 +00:00
|
|
|
.\" All rights reserved.
|
|
|
|
|
.\"
|
|
|
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
|
|
|
.\" modification, are permitted provided that the following conditions
|
|
|
|
|
.\" are met:
|
|
|
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
|
|
|
.\" notice(s), this list of conditions and the following disclaimer as
|
|
|
|
|
.\" the first lines of this file unmodified other than the possible
|
|
|
|
|
.\" addition of one or more copyright notices.
|
|
|
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
|
|
|
.\" notice(s), this list of conditions and the following disclaimer in
|
|
|
|
|
.\" the documentation and/or other materials provided with the
|
|
|
|
|
.\" distribution.
|
|
|
|
|
.\"
|
|
|
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
|
|
|
|
|
.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
|
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
|
|
|
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
|
|
|
|
|
.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
|
|
|
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
|
|
|
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
|
|
|
|
|
.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
|
|
|
|
|
.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
|
|
|
|
|
.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
|
|
|
|
|
.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
|
|
|
.\"
|
|
|
|
|
.\" $FreeBSD$
|
|
|
|
|
.Dd February 15, 2000
|
|
|
|
|
.Dt SEM_WAIT 3
|
|
|
|
|
.Os
|
|
|
|
|
.Sh NAME
|
|
|
|
|
.Nm sem_wait ,
|
|
|
|
|
.Nm sem_trywait
|
|
|
|
|
.Nd decrement (lock) a semaphore
|
2000-04-22 15:50:29 +00:00
|
|
|
.Sh LIBRARY
|
|
|
|
|
.Lb libc_r
|
2000-02-16 19:31:53 +00:00
|
|
|
.Sh SYNOPSIS
|
|
|
|
|
.Fd #include <semaphore.h>
|
|
|
|
|
.Ft int
|
|
|
|
|
.Fn sem_wait "sem_t *sem"
|
|
|
|
|
.Ft int
|
|
|
|
|
.Fn sem_trywait "sem_t *sem"
|
|
|
|
|
.Sh DESCRIPTION
|
|
|
|
|
The
|
|
|
|
|
.Fn sem_wait
|
|
|
|
|
function decrements (locks) the semaphore pointed to by
|
|
|
|
|
.Fa sem ,
|
|
|
|
|
but blocks if the value of
|
|
|
|
|
.Fa sem
|
|
|
|
|
is zero, until the value is non-zero and the value can be decremented.
|
|
|
|
|
.Pp
|
|
|
|
|
The
|
|
|
|
|
.Fn sem_trywait
|
|
|
|
|
function decrements (locks) the semaphore pointed to by
|
|
|
|
|
.Fa sem
|
|
|
|
|
only if the value is non-zero. Otherwise, the semaphore is not decremented and
|
|
|
|
|
an error is returned.
|
|
|
|
|
.Sh RETURN VALUES
|
|
|
|
|
If successful,
|
|
|
|
|
.Fn sem_wait
|
|
|
|
|
and
|
|
|
|
|
.Fn sem_trywait
|
|
|
|
|
return 0. Otherwise, -1 is returned and
|
|
|
|
|
.Va errno
|
|
|
|
|
is set to indicate the type of
|
|
|
|
|
error.
|
|
|
|
|
.Sh ERRORS
|
|
|
|
|
.Fn sem_wait
|
|
|
|
|
and
|
|
|
|
|
.Fn sem_trywait
|
|
|
|
|
will fail if:
|
|
|
|
|
.Bl -tag -width Er
|
|
|
|
|
.It Bq Er EINVAL
|
|
|
|
|
.Fa sem
|
|
|
|
|
points to an invalid semaphore.
|
|
|
|
|
.El
|
|
|
|
|
.Pp
|
|
|
|
|
Additionally,
|
|
|
|
|
.Fn sem_trywait
|
|
|
|
|
will fail if:
|
|
|
|
|
.Bl -tag -width Er
|
|
|
|
|
.It Bq Er EAGAIN
|
|
|
|
|
The semaphore value was zero, and thus could not be decremented.
|
|
|
|
|
.El
|
|
|
|
|
.Sh SEE ALSO
|
|
|
|
|
.Xr sem_post 3
|
|
|
|
|
.Sh STANDARDS
|
|
|
|
|
.Fn sem_wait
|
|
|
|
|
and
|
|
|
|
|
.Fn sem_trywait
|
2001-02-26 15:16:43 +00:00
|
|
|
conform to
|
|
|
|
|
.St -p1003.1-96 .
|
