Background Operation #

A small set of C functions manages RPCL background operation. Actually this set of functions is independent from RPCL, it works with any application communicating through the standard stdin/stdout/stderr file descriptors.

All functions require root permissions (geteuid() == 0 is true).
The named pipes, .pid-files and necessary lock files are managed in /run (where /var/run symbolically links to).

Backend Functions #

CTLDaemonize() #

This function “daemonizes” the current application and registers it with the specified identifier.

If there is already a background process running with the same identifier, an error is signalled.
This function needs to be called before any memory mapping or additional threads are started.
Internally daemon() is called with the request to change directory and leaving the redirected standard file descriptors open.

void CTLDaemonize(char* identifier);

Frontend Functions #

CTLFrontend() #

This connects to a running backend with basic line editing.
Only one session can be active at one time.
There’s an inactivity timeout of 10 minutes.
On start a newline (empty line) is sent to the backend for synchronization (which leads to the initial ok prompt when connected to an RPCL interpreter instance).
The frontend session can be terminated with EOF (^D) or ^C.

void CTLFrontend(char* identifier);

CTLStatus() #

void CTLStatus(char* identifier);

CTLStop() #

void CTLStop(char* identifier);

An Example: `ctltest` #

This is how a RPCL interpreter may be instantiated to run in background with the identifier ctltest:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18


#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <rpcl.h>
#include <ctl.h>

int main(int argc, char** argv) {

  RPCL* rpcl;

  CTLDaemonize("ctltest");

  rpcl = RPCLCreate(argc, argv);
  RPCLMainLoop(rpcl);
  RPCLDestroy(rpcl);
  exit(EXIT_SUCCESS);
}

The `control` Frontend #

The control program makes the CTL frontend functions available like this:

$ ./control -h
usage: control <identifier>          control background process
       control <identifier> status   show background process status
       control <identifier> stop     terminate background process
       control -h|--help             show usage
       control -v|--version          show version
       control -c|--copyright        show copyright
$ ▂

This is an example dialog:

$ sudo ./control ctltest status
ctltest not running
$ sudo ./ctltest
ctltest going to background ...
$ sudo ./control ctltest status
ctltest PID 7098 running
$ sudo ./control ctltest
connected to ctltest PID 7098
ok .d
version.rpcl                     1.58
ok ▂