'\" t .\" Copyright (C) 2006 Michael Kerrisk .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .TH sem_getvalue 3 2023-10-31 "Linux man-pages 6.06" .SH NAME sem_getvalue \- get the value of a semaphore .SH LIBRARY POSIX threads library .RI ( libpthread ", " \-lpthread ) .SH SYNOPSIS .nf .B #include .P .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 . .P 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 .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)