1.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as 9.\" the first lines of this file unmodified other than the possible 10.\" addition of one or more copyright notices. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice(s), this list of conditions and the following disclaimer in 13.\" the documentation and/or other materials provided with the 14.\" distribution. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 17.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 19.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE 20.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 21.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 22.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 23.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 24.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 25.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 26.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27.\" 28.\" $FreeBSD$ 29.Dd February 15, 2000 30.Dt SEM_GETVALUE 3 31.Os 32.Sh NAME 33.Nm sem_getvalue 34.Nd get the value of a semaphore 35.Sh SYNOPSIS 36.Fd #include <semaphore.h> 37.Ft int 38.Fn sem_getvalue "sem_t *sem" "int *sval" 39.Sh DESCRIPTION 40The 41.Fn sem_getvalue 42function sets the variable pointed to by 43.Fa sval 44to the current value of the semaphore pointed to by 45.Fa sem , 46as of the time that the call to 47.Fn sem_getvalue 48is actually run. 49.Sh RETURN VALUES 50If successful, 51.Fn sem_getvalue 52returns 0. Otherwise, -1 is returned and 53.Va errno 54is set to indicate the type of 55error. 56.Sh ERRORS 57.Fn sem_getvalue 58will fail if: 59.Bl -tag -width Er 60.It Bq Er EINVAL 61.Fa sem 62points to an invalid semaphore. 63.El 64.Sh SEE ALSO 65.Xr sem_post 3 , 66.Xr sem_wait 3 , 67.Xr sem_trywait 3 68.Sh STANDARDS 69.Fn sem_getvalue 70conforms to ISO/IEC 9945-1 ANSI/IEEE 71.Pq Dq Tn POSIX 72Std 1003.1 1996 Edition. 73.Pp 74The value of the semaphore is never negative, even if there are threads blocked 75on the semaphore. POSIX is somewhat ambiguous in its wording with regard to 76what the value of the semaphore should be if there are blocked waiting threads, 77but this behavior is conformant, given the wording of the specification. 78