.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>.
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.\" $FreeBSD: src/lib/libc_r/man/sigwait.3,v 1.7 2001/10/01 16:09:09 ru Exp $
.Dd April 27, 2000
.Dt SIGWAIT 2
.Os
.Sh NAME
.Nm sigwait
.Nd select a set of signals
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigwait "const sigset_t *restrict set" "int *restrict sig"
.Sh DESCRIPTION
The
.Fn sigwait
function 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, but not ignored, at the time of the call to
.Fn sigwait .
.Pp
Processes which call 
.Fn sigwait
on ignored signals will wait indefinitely.  Ignored 
signals are dropped immediately by the system, before delivery 
to a waiting process.
.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
.Fn sigwait
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa set
specifies one or more invalid signal numbers.
.El
.Sh SEE ALSO
.Xr pthread_sigmask 2 ,
.Xr sigaction 2 ,
.Xr sigpending 2 ,
.Xr sigsuspend 2 ,
.Xr pause 3
.Sh STANDARDS
.Fn sigwait
conforms to ISO/IEC 9945-1:1996 (``POSIX.1'')