man sigqueue (2): queue a signal to a process (REALTIME)

LIBRARY

Lb libc

SYNOPSIS

In signal.h Ft int Fn sigqueue pid_t pid int signo const union sigval value

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.

The conditions required for a process to have permission to queue a signal to another process are the same as for the kill(2) system call. The Fn sigqueue system call queues a signal to a single process specified by the Fa pid argument.

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.

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 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.

RETURN VALUES

Rv -std

ERRORS

The Fn sigqueue system call will fail if:

Bq Er EAGAIN: No resources are available to queue the signal. The process has already queued Br q Dv SIGQUEUE_MAX signals that are still pending at the receiver(s), or a system-wide resource limit has been exceeded.
Bq Er EINVAL: The value of the Fa signo argument is an invalid or unsupported signal number.
Bq Er EPERM: The process does not have the appropriate privilege to send the signal to the receiving process.
Bq Er ESRCH: The process Fa pid does not exist.

STANDARDS

The Fn sigqueue system call conforms to St -p1003.1-2004 .

HISTORY

Support for POSIX realtime signal queue first appeared in Fx 7.0 .