1 .\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .TH SEM_GETVALUE 3 2021-03-22 "Linux" "Linux Programmer's Manual"
27 sem_getvalue \- get the value of a semaphore
30 .B #include <semaphore.h>
32 .BI "int sem_getvalue(sem_t *restrict " sem ", int *restrict " sval );
35 Link with \fI\-pthread\fP.
38 places the current value of the semaphore pointed to
40 into the integer pointed to by
43 If one or more processes or threads are blocked
44 waiting to lock the semaphore with
46 POSIX.1 permits two possibilities for the value returned in
49 or a negative number whose absolute value is the count
50 of the number of processes and threads currently blocked in
52 Linux adopts the former behavior.
56 on error, \-1 is returned and
58 is set to indicate the error.
63 is not a valid semaphore.
64 (The glibc implementation currently does not check whether
68 For an explanation of the terms used in this section, see
76 Interface Attribute Value
79 T} Thread safety MT-Safe
85 POSIX.1-2001, POSIX.1-2008.
87 The value of the semaphore may already have changed by the time