xref: /freebsd-14.2/lib/libc/sys/sigqueue.2 (revision 5507a2ae)

.\" Copyright (c) 2005 David Xu <[email protected]>
.\" 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 November 11, 2005
.Dt SIGQUEUE 2
.Os
.Sh NAME
.Nm sigqueue
.Nd "queue a signal to a process (REALTIME)"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigqueue "pid_t pid" "int signo" "const union sigval value"
.Sh DESCRIPTION
The
.Fn sigqueue
system call causes the signal specified by
.Fa signo
to be sent with the value specified by
.Fa value
to the process specified by
.Fa pid .
If
.Fa signo
is zero (the null signal), error checking is performed but
no signal is actually sent.
The null signal can be used to check the
validity of PID.
.Pp
The conditions required for a process to have permission to queue a
signal to another process are the same as for the
.Xr kill 2
system call.
The
.Fn sigqueue
system call queues a signal to a single process specified by the
.Fa pid
argument.
.Pp
The
.Fn sigqueue
system call returns immediately.
If the resources were
available to queue the signal, the signal will be queued and sent to
the receiving process.
.Pp
If the value of
.Fa pid
causes
.Fa signo
to be generated for the sending process, and if
.Fa signo
is not blocked for the calling thread and if no other thread has
.Fa signo
unblocked or is waiting in a
.Fn sigwait
system call for
.Fa signo ,
either
.Fa signo
or at least the pending, unblocked signal will be delivered to the
calling thread before
.Fn sigqueue
returns.
Should any multiple pending signals in the range
.Dv SIGRTMIN
to
.Dv SIGRTMAX
be selected for delivery, it is the lowest numbered
one.
The selection order between realtime and non-realtime signals, or
between multiple pending non-realtime signals, is unspecified.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The
.Fn sigqueue
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
No resources are available to queue the signal.
The process has already
queued
.Brq Dv SIGQUEUE_MAX
signals that are still pending at the receiver(s),
or a system-wide resource limit has been exceeded.
.It Bq Er EINVAL
The value of the
.Fa signo
argument is an invalid or unsupported signal number.
.It Bq Er EEPERM
The process does not have the appropriate privilege to send the signal
to the receiving process.
.It Bq Er ESRCH
The process
.Fa pid
does not exist.
.El
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigpending 2 ,
.Xr sigqueue 2 ,
.Xr sigsuspend 2 ,
.Xr sigtimedwait 2 ,
.Xr sigwait 2 ,
.Xr sigwaitinfo 2 ,
.Xr pause 3 ,
.Xr pthread_sigmask 3
.Sh STANDARDS
The
.Fn sigqueue
system call conforms to
.St -p1003.1-96 .