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another POSIX compliance fix: sigwait(3) should not use errno but
return the error code directly

.\" $NetBSD: sigtimedwait.2,v 1.7 2010/05/31 11:02:24 drochner Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jaromir Dolecek.
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.Dd May 30, 2010
.Dt SIGTIMEDWAIT 2
.Os
.Sh NAME
.Nm sigtimedwait ,
.Nm sigwaitinfo ,
.Nm sigwait
.Nd wait for queued signals
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigtimedwait "const sigset_t * restrict set" "siginfo_t * restrict info" "const struct timespec * restrict timeout"
.Ft int
.Fn sigwaitinfo "const sigset_t * restrict set" "siginfo_t * restrict info"
.Ft int
.Fn sigwait "const sigset_t * restrict set" "int * restrict sig"
.Sh DESCRIPTION
.Fn sigwaitinfo
and
.Fn sigwait
return the first pending signal from the set specified by
.Fa set .
Should multiple signals from
.Fa set
be pending, the lowest numbered one is returned.
The selection order between realtime and non-realtime signals is unspecified.
If there is no signal from
.Ar set
pending at the time of the call, the calling thread
is suspended until one of the specified signals is generated.
.Pp
.Fn sigtimedwait
is exactly equal to
.Fn sigwaitinfo ,
except
.Fa timeout
specifies the maximum time interval for which the calling thread will
be suspended.
If
.Fa timeout
is zero (tv_sec == tv_nsec == 0),
.Fn sigtimedwait
only checks the currently pending signals and returns immediately.
If
.Dv NULL
is used for
.Fa timeout ,
.Fn sigtimedwait
behaves exactly like
.Fn sigwaitinfo
in all regards.
.Pp
If several threads are waiting for a given signal, exactly one of them
returns from the signal wait when the signal is generated.
.Pp
Behaviour of these functions is unspecified if any of the signals in
.Fa set
are unblocked at the time these functions are called.
.Sh RETURN VALUES
Upon successful completion of
.Fn sigtimedwait
or
.Fn sigwaitinfo
.Fa info
is updated with signal information, and the function returns the signal number.
Otherwise, \-1 is returned and the global variable
.Va errno
indicates the error.
Upon successful completion of
.Fn sigwait
.Fa sig
is updated with ihe signal number, and the function returns 0.
Otherwise, a non-zero error code is returned,
.Sh ERRORS
.Fn sigwaitinfo
and
.Fn sigwait
always succeed.
.Pp
.Fn sigtimedwait
will fail and the
.Fa info
pointer will remain unchanged if:
.Bl -tag -width Er
.It Bq Er EAGAIN
No signal specified in
.Fa set
was generated in the specified
.Fa timeout .
.El
.Pp
.Fn sigtimedwait
may also fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The specified
.Fa timeout
was invalid.
.El
.Pp
This error is only checked if no signal from
.Fa set
is pending and it would be necessary to wait.
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigprocmask 2 ,
.Xr signal 7
.Sh STANDARDS
The functions
.Fn sigtimedwait ,
.Fn sigwaitinfo ,
and
.Fn sigwait
conform to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn sigtimedwait ,
.Fn sigwaitinfo ,
and
.Fn sigwait
functions appeared in
.Nx 2.0 .