mirror of https://github.com/mkerrisk/man-pages
75 lines
2.3 KiB
Groff
75 lines
2.3 KiB
Groff
'\" t
|
|
.\" 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.\" manual page may be incorrect or out-of-date.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.
|
|
.\"
|
|
.TH SEM_GETVALUE 3 2006-03-25 "Linux" "Linux Programmer's Manual"
|
|
.SH NAME
|
|
sem_getvalue \- get the value of a semaphore
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.B #include <semaphore.h>
|
|
.sp
|
|
.BI "int sem_getvalue(sem_t *" sem ", int *" sval );
|
|
.fi
|
|
.sp
|
|
Link with \fI\-lrt\fP or \fI\-pthread\fP.
|
|
.SH DESCRIPTION
|
|
.BR sem_getvalue ()
|
|
places the current value of the semaphore pointed to
|
|
.I sem
|
|
into the integer pointed to by
|
|
.IR sval .
|
|
|
|
If one or more processes or threads are blocked
|
|
waiting to lock the semaphore with
|
|
.BR sem_wait (3),
|
|
POSIX.1-2001 permits two possibilities for the value returned in
|
|
.IR sval :
|
|
either 0 is returned;
|
|
or a negative number whose absolute value is the count
|
|
of the number of processes and threads currently blocked in
|
|
.BR sem_wait (3).
|
|
Linux adopts the former behavior.
|
|
.SH RETURN VALUE
|
|
.BR sem_getvalue ()
|
|
returns 0 on success;
|
|
on error, \-1 is returned and
|
|
.I errno
|
|
is set to indicate the error.
|
|
.SH ERRORS
|
|
.TP
|
|
.B EINVAL
|
|
.I sem
|
|
is not a valid semaphore.
|
|
.SH CONFORMING TO
|
|
POSIX.1-2001.
|
|
.SH NOTES
|
|
The value of the semaphore may already have changed by the time
|
|
.BR sem_getvalue ()
|
|
returns.
|
|
.SH "SEE ALSO"
|
|
.BR sem_post (3),
|
|
.BR sem_wait (3),
|
|
.BR sem_overview (7)
|