1.\" Copyright (C) 2000 Jason Evans <[email protected]>. 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 September 6, 2013 31.Dt SIGWAIT 2 32.Os 33.Sh NAME 34.Nm sigwait 35.Nd select a set of signals 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In signal.h 40.Ft int 41.Fn sigwait "const sigset_t * restrict set" "int * restrict sig" 42.Sh DESCRIPTION 43The 44.Fn sigwait 45system call selects a set of signals, specified by 46.Fa set . 47If none of the selected signals are pending, 48.Fn sigwait 49waits until one or more of the selected signals has been generated. 50Then 51.Fn sigwait 52atomically clears one of the selected signals from the set of pending signals 53(for the process or for the current thread) and sets the location pointed to by 54.Fa sig 55to the signal number that was cleared. 56.Pp 57The signals specified by 58.Fa set 59should be blocked at the time of the call to 60.Fn sigwait . 61.Pp 62If more than one thread is using 63.Fn sigwait 64to wait for the same signal, no more than one of these threads will return from 65.Fn sigwait 66with the signal number. 67If more than a single thread is blocked in 68.Fn sigwait 69for a signal when that signal is generated for the process, it is unspecified 70which of the waiting threads returns from 71.Fn sigwait . 72If the signal is generated for a specific thread, as by 73.Fn pthread_kill , 74only that thread will return. 75.Pp 76Should any of the multiple pending signals in the range 77.Dv SIGRTMIN 78to 79.Dv SIGRTMAX 80be 81selected, it will be the lowest numbered one. 82The selection order between realtime 83and non-realtime signals, or between multiple pending non-realtime signals, 84is unspecified. 85.Sh IMPLEMENTATION NOTES 86The 87.Fn sigwait 88function is implemented as a wrapper around the 89.Fn __sys_sigwait 90system call, which retries the call on 91.Er EINTR 92error. 93.Sh RETURN VALUES 94If successful, 95.Fn sigwait 96returns 0 and sets the location pointed to by 97.Fa sig 98to the cleared signal number. 99Otherwise, an error number is returned. 100.Sh ERRORS 101The 102.Fn sigwait 103system call will fail if: 104.Bl -tag -width Er 105.It Bq Er EINVAL 106The 107.Fa set 108argument 109specifies one or more invalid signal numbers. 110.El 111.Sh SEE ALSO 112.Xr sigaction 2 , 113.Xr sigpending 2 , 114.Xr sigqueue 2 , 115.Xr sigsuspend 2 , 116.Xr sigtimedwait 2 , 117.Xr sigwaitinfo 2 , 118.Xr pause 3 , 119.Xr pthread_sigmask 3 120.Sh STANDARDS 121The 122.Fn sigwait 123function conforms to 124.St -p1003.1-96 . 125