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.Dd January 28, 2015 29.Dt SEM_POST 3 30.Os 31.Sh NAME 32.Nm sem_post 33.Nd increment (unlock) a semaphore 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In semaphore.h 38.Ft int 39.Fn sem_post "sem_t *sem" 40.Sh DESCRIPTION 41The 42.Fn sem_post 43function increments (unlocks) the semaphore pointed to by 44.Fa sem . 45If there are threads blocked on the semaphore when 46.Fn sem_post 47is called, then the highest priority thread that has been blocked the longest on 48the semaphore will be allowed to return from 49.Fn sem_wait . 50.Pp 51The 52.Fn sem_post 53function is signal-reentrant and may be called within signal handlers. 54.Sh RETURN VALUES 55.Rv -std sem_post 56.Sh ERRORS 57The 58.Fn sem_post 59function will fail if: 60.Bl -tag -width Er 61.It Bq Er EINVAL 62The 63.Fa sem 64argument 65points to an invalid semaphore. 66.It Bq Er EOVERFLOW 67The semaphore value would exceed 68.Dv SEM_VALUE_MAX . 69.El 70.Sh SEE ALSO 71.Xr sem_getvalue 3 , 72.Xr sem_trywait 3 , 73.Xr sem_wait 3 74.Sh STANDARDS 75The 76.Fn sem_post 77function conforms to 78.St -p1003.1-96 . 79