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+'\" t
+.\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH sem_getvalue 3 2023-07-20 "Linux man-pages 6.05.01"
+.SH NAME
+sem_getvalue \- get the value of a semaphore
+.SH LIBRARY
+POSIX threads library
+.RI ( libpthread ", " \-lpthread )
+.SH SYNOPSIS
+.nf
+.B #include <semaphore.h>
+.PP
+.BI "int sem_getvalue(sem_t *restrict " sem ", int *restrict " sval );
+.fi
+.SH DESCRIPTION
+.BR sem_getvalue ()
+places the current value of the semaphore pointed to
+.I sem
+into the integer pointed to by
+.IR sval .
+.PP
+If one or more processes or threads are blocked
+waiting to lock the semaphore with
+.BR sem_wait (3),
+POSIX.1 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.
+(The glibc implementation currently does not check whether
+.I sem
+is valid.)
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR sem_getvalue ()
+T}	Thread safety	MT-Safe
+.TE
+.sp 1
+.SH STANDARDS
+POSIX.1-2008.
+.SH HISTORY
+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)