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Full Discussion: Simple capturing of keyboard input without interruption
Top Forums Programming Simple capturing of keyboard input without interruption Post 303014186 by jim mcnamara on Tuesday 6th of March 2018 03:40:41 PM
Old 03-06-2018
Overview:
I'm not going to figure out all of the above wall of code. This example is how MS windows and X work. A simple, fairly stupid, event (message) pump that does nothing but read stdin, then send it off to a pipe. The little one I call "tiny" your code wall is "big" and it needs to dup() stdin on startup.

What you will do is to steal a tiny bit of windowing architecture - as in a message pump:
interpose a tiny program that loops and reads each character from stdin and then sends everything it gets from stdin to a pipe -except the <return> key. It exits or whatever you need on the return key.

Start the tiny program, have it fork your large program as a child that reads input from a pipe. Big's code can live in the same physical code that tiny lives in. Call fork() on the "big" entry point.

Tiny reads everything and simply passes it on, except in your case tiny exits when the ASCII 13 character (\n) is read. Tiny has almost zero smarts, just calls signal(), read(), wait() and pipe().

If tiny wants to quit: signal big, call wait() on big, then exit().
If big wants to quit: signal tiny, then exit() Tiny's signal handler gets the signal and exits.

If you really get stuck, post your attempt. If executable code lines in the tiny program code exceeds circa 50 lines or so your logic is probably too complex. Add bells and whistles after it works.
This User Gave Thanks to jim mcnamara For This Post:
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LEARN ABOUT DEBIAN

runsv

runsv(8)						      System Manager's Manual							  runsv(8)

NAME

       runsv - starts and monitors a service and optionally an appendant log service

SYNOPSIS

       runsv service

DESCRIPTION

       service must be a directory.

       runsv  switches to the directory service and starts ./run.  If ./run exits and ./finish exists, runsv starts ./finish.  If ./finish doesn't
       exist or ./finish exits, runsv restarts ./run.

       If ./run or ./finish exit immediately, runsv waits a second before starting ./finish or restarting ./run.

       Two arguments are given to ./finish.  The first one is ./run's exit code, or -1 if ./run didn't exit normally.  The second one is the least
       significant  byte  of  the exit status as determined by waitpid(2); for instance it is 0 if ./run exited normally, and the signal number if
       ./run was terminated by a signal.  If runsv cannot start ./run for some reason, the exit code is 111 and the status is 0.

       If the file service/down exists, runsv does not start ./run immediately.  The control interface (see below) can be used to start  the  ser-
       vice and to give other commands to runsv.

       If  the	directory  service/log	exists,  runsv	creates  a pipe, redirects service/run's and service/finish's standard output to the pipe,
       switches to the directory service/log and starts ./run (and ./finish) exactly as described above for the service directory.   The  standard
       input of the log service is redirected to read from the pipe.

       runsv  maintains  status  information in a binary format (compatible to the daemontools' supervise program) in service/supervise/status and
       service/log/supervise/status, and in a human-readable format in service/supervise/stat, service/log/supervise/stat,  service/supervise/pid,
       service/log/supervise/pid.

CONTROL

       The  named pipes service/supervise/control, and (optionally) service/log/supervise/control are provided to give commands to runsv.  You can
       use sv(8) to control the service or just write one of the following characters to the named pipe:

       u      Up.  If the service is not running, start it.  If the service stops, restart it.

       d      Down.  If the service is running, send it a TERM signal, and then a CONT signal.	If ./run  exits,  start  ./finish  if  it  exists.
	      After it stops, do not restart service.

       o      Once.  If the service is not running, start it.  Do not restart it if it stops.

       p      Pause.  If the service is running, send it a STOP signal.

       c      Continue.  If the service is running, send it a CONT signal.

       h      Hangup.  If the service is running, send it a HUP signal.

       a      Alarm.  If the service is running, send it a ALRM signal.

       i      Interrupt.  If the service is running, send it a INT signal.

       q      Quit.  If the service is running, send it a QUIT signal.

       1      User-defined 1.  If the service is running, send it a USR1 signal.

       2      User-defined 2.  If the service is running, send it a USR2 signal.

       t      Terminate.  If the service is running, send it a TERM signal.

       k      Kill.  If the service is running, send it a KILL signal.

       x      Exit.   If  the  service	is running, send it a TERM signal, and then a CONT signal.  Do not restart the service.  If the service is
	      down, and no log service exists, runsv exits.  If the service is down and a log service exists, runsv closes the standard  input	of
	      the log service, and waits for it to terminate.  If the log service is down, runsv exits.  This command is ignored if it is given to
	      service/log/supervise/control.

       Example: to send a TERM signal to the socklog-unix service, either do
	 # sv term /etc/service/socklog-unix
	or
	 # printf t >/etc/service/socklog-unix/supervise/control

       printf(1) usually blocks if no runsv process is running in the service directory.

CUSTOMIZE CONTROL

       For each control character c sent to the control pipe, runsv first checks if service/control/c exists and is executable.  If so, it  starts
       service/control/c  and waits for it to terminate, before interpreting the command.  If the program exits with return code 0, runsv refrains
       from sending the service the corresponding signal.  The command o is always considered as command u.  On command d first  service/control/t
       is  checked,  and then service/control/d.  On command x first service/control/t is checked, and then service/control/x.	The control of the
       optional log service cannot be customized.

SIGNALS

       If runsv receives a TERM signal, it acts as if the character x was written to the control pipe.

EXIT CODES

       runsv exits 111 on an error on startup or if another runsv is running in service.

       runsv exits 0 if it was told to exit.

SEE ALSO

       sv(8), chpst(8), svlogd(8), runit(8), runit-init(8), runsvdir(8), runsvchdir(8), utmpset(8)

       http://smarden.org/runit/

AUTHOR

       Gerrit Pape <pape@smarden.org>

																	  runsv(8)
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