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.so man2/rename.2
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.\" copyright (c) 2006 michael kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%license_start(verbatim)
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.\" permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\" permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\" since the linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. the author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. the author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\" formatted or processed versions of this manual, if unaccompanied by
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.\" %%%license_end
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.\"
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.th sem_getvalue 3 2021-03-22 "linux" "linux programmer's manual"
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.sh name
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sem_getvalue \- get the value of a semaphore
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.sh synopsis
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.nf
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.b #include <semaphore.h>
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.pp
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.bi "int sem_getvalue(sem_t *restrict " sem ", int *restrict " sval );
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.fi
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.pp
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link with \fi\-pthread\fp.
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.sh description
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.br sem_getvalue ()
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places the current value of the semaphore pointed to
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.i sem
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into the integer pointed to by
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.ir sval .
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.pp
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if one or more processes or threads are blocked
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waiting to lock the semaphore with
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.br sem_wait (3),
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posix.1 permits two possibilities for the value returned in
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.ir sval :
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either 0 is returned;
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or a negative number whose absolute value is the count
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of the number of processes and threads currently blocked in
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.br sem_wait (3).
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linux adopts the former behavior.
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.sh return value
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.br sem_getvalue ()
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returns 0 on success;
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on error, \-1 is returned and
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.i errno
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is set to indicate the error.
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.sh errors
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.tp
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.b einval
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.i sem
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is not a valid semaphore.
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(the glibc implementation currently does not check whether
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.i sem
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is valid.)
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.sh attributes
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for an explanation of the terms used in this section, see
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.br attributes (7).
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.ad l
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.nh
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.ts
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allbox;
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lbx lb lb
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l l l.
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interface attribute value
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t{
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.br sem_getvalue ()
|
t} thread safety mt-safe
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.te
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.hy
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.ad
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.sp 1
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.sh conforming to
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posix.1-2001, posix.1-2008.
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.sh notes
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the value of the semaphore may already have changed by the time
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.br sem_getvalue ()
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returns.
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.sh see also
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.br sem_post (3),
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.br sem_wait (3),
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.br sem_overview (7)
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.sh colophon
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this page is part of release 5.13 of the linux
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.i man-pages
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project.
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a description of the project,
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