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.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice(s), this list of conditions and the following disclaimer as
.\" the first lines of this file unmodified other than the possible
.\" addition of one or more copyright notices.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice(s), this list of conditions and the following disclaimer in
.\" the documentation and/or other materials provided with the
.\" distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd September 27, 2012
.Dt SIGWAIT 2
.Os
.Sh NAME
.Nm sigwait
.Nd select a set of signals
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigwait "const sigset_t * restrict set" "int * restrict sig"
.Sh DESCRIPTION
The
.Fn sigwait
system call selects a set of signals, specified by
.Fa set .
If none of the selected signals are pending,
.Fn sigwait
waits until one or more of the selected signals has been generated.
Then
.Fn sigwait
atomically clears one of the selected signals from the set of pending signals
for the process and sets the location pointed to by
.Fa sig
to the signal number that was cleared.
.Pp
The signals specified by
.Fa set
should be blocked at the time of the call to
.Fn sigwait .
.Pp
If more than one thread is using
.Fn sigwait
to wait for the same signal, no more than one of these threads will return from
.Fn sigwait
with the signal number.
If more than a single thread is blocked in
.Fn sigwait
for a signal when that signal is generated for the process, it is unspecified
which of the waiting threads returns from
.Fn sigwait .
If the signal is generated for a specific thread, as by
.Fn pthread_kill ,
only that thread will return.
.Pp
Should any of the multiple pending signals in the range
.Dv SIGRTMIN
to
.Dv SIGRTMAX
be
selected, it will be the lowest numbered one.
The selection order between realtime
and non-realtime signals, or between multiple pending non-realtime signals,
is unspecified.
.Sh IMPLEMENTATION NOTES
The
.Fn sigwait
function is implemented as a wrapper around the
.Fn __sys_sigwait
system call, which retries the call on
.Er EINTR
error.
.Sh RETURN VALUES
If successful,
.Fn sigwait
returns 0 and sets the location pointed to by
.Fa sig
to the cleared signal number.
Otherwise, an error number is returned.
.Sh ERRORS
The
.Fn sigwait
system call will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa set
argument
specifies one or more invalid signal numbers.
.El
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigpending 2 ,
.Xr sigqueue 2 ,
.Xr sigsuspend 2 ,
.Xr sigtimedwait 2 ,
.Xr sigwaitinfo 2 ,
.Xr pause 3 ,
.Xr pthread_sigmask 3
.Sh STANDARDS
The
.Fn sigwait
function conforms to
.St -p1003.1-96 .
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