xref: /freebsd-14.2/lib/libc/sys/sigqueue.2 (revision e84ece6b)

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.Dd Nov 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
function 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
.Fn kill
function.
The
.Fn sigqueue
function queues a signal to a single process specified by the pid argument.
.Pp
The sigqueue() function 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
function for
.Fa signo, either
.Fa signo
or at least the pending, unblocked signal will be delivered to the
calling thread before the
.Fn sigqueue
function returns. Should any multiple pending signals in the range
SIGRTMIN to 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
Upon successful completion, the specified signal has been queued, and
the
.Fn sigqueue
function returns a value of zero. Otherwise, the function returns a value
of -1 and set errno to indicate the error.
.Sh ERRORS
The
.Fn sigqueue
will fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
No resources are available to queue the signal. The process has already
queued {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 pid does not exist.
.El
.Sh SEE ALSO
.Xr sigwait 2 ,
.Xr sigtimedwait 2 ,
.Xr sigwaitinfo 2 ,
.Xr sigqueue 2 ,
.Xr sigaction 2 ,
.Xr sigpending 2 ,
.Xr sigsuspend 2 ,
.Xr pause 3 ,
.Xr pthread_sigmask 3
.Sh STANDARDS
The
.Fn sigqueue
function conforms to
.St -p1003.1-96 .