1.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>. 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.\" 30.Dd January 28, 2015 31.Dt SEM_POST 3 32.Os 33.Sh NAME 34.Nm sem_post 35.Nd increment (unlock) a semaphore 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In semaphore.h 40.Ft int 41.Fn sem_post "sem_t *sem" 42.Sh DESCRIPTION 43The 44.Fn sem_post 45function increments (unlocks) the semaphore pointed to by 46.Fa sem . 47If there are threads blocked on the semaphore when 48.Fn sem_post 49is called, then the highest priority thread that has been blocked the longest on 50the semaphore will be allowed to return from 51.Fn sem_wait . 52.Pp 53The 54.Fn sem_post 55function is signal-reentrant and may be called within signal handlers. 56.Sh RETURN VALUES 57.Rv -std sem_post 58.Sh ERRORS 59The 60.Fn sem_post 61function will fail if: 62.Bl -tag -width Er 63.It Bq Er EINVAL 64The 65.Fa sem 66argument 67points to an invalid semaphore. 68.It Bq Er EOVERFLOW 69The semaphore value would exceed 70.Dv SEM_VALUE_MAX . 71.El 72.Sh SEE ALSO 73.Xr sem_getvalue 3 , 74.Xr sem_trywait 3 , 75.Xr sem_wait 3 76.Sh STANDARDS 77The 78.Fn sem_post 79function conforms to 80.St -p1003.1-96 . 81