Re: system-question

[Mats Jansson]

Thanks Joao!
You introduced the command 'fork' to me!

Unfortunately, a new problem appeared. When I'm killing emacs from the
octave-prompt, everything seems to work. But when I'm killing it from
a function, it becomes a zombie-process.

Does anyone have a solution?

Thanks
Mats

address@hidden ~]$ octave
GNU Octave, version 2.0.14 (i386-redhat-linux-gnu).
Copyright (C) 1996, 1997, 1998, 1999 John W. Eaton.
This is free software with ABSOLUTELY NO WARRANTY.
For details, type `warranty'.

octave:1> pid=launch ("emacs","dummy")
pid = 18807
octave:2> system ("ps f")
  PID TTY      STAT   TIME COMMAND
18296 pts/3    S      0:00 -csh
18804 pts/3    S      0:00 octave
18807 pts/3    S      0:01  \_ emacs dummy
18808 pts/3    R      0:00  \_ ps f
ans = 0
octave:3> system (["kill ", num2str(pid)])
ans = 0
octave:4> system ("ps f")
  PID TTY      STAT   TIME COMMAND
18296 pts/3    S      0:00 -csh
18804 pts/3    S      0:00 octave
18810 pts/3    R      0:00  \_ ps f
ans = 0
octave:5> function retval=kill(pid)
> retval=system (["kill ", num2str(pid)]);
> endfunction
octave:6> pid=launch ("emacs","dummy")
pid = 18811
octave:7> system ("ps f")
  PID TTY      STAT   TIME COMMAND
18296 pts/3    S      0:00 -csh
18804 pts/3    S      0:00 octave
18811 pts/3    S      0:01  \_ emacs dummy
18812 pts/3    R      0:00  \_ ps f
ans = 0
octave:8> kill (pid)
ans = 
octave:9> system ("ps f")
  PID TTY      STAT   TIME COMMAND
18296 pts/3    S      0:00 -csh
18804 pts/3    S      0:00 octave
18811 pts/3    Z      0:01  \_ [emacs <defunct>]
18814 pts/3    R      0:00  \_ ps f
ans = 0
octave:10> 

Joao Cardoso wrote:

> Mats Jansson wrote:
> 
>> Hi!
>>
>> I want to start a program in the background from octave. I want to be
>> able to check if the program is still running and I want to be able to
>> close the program from octave.
>>
>> My idea was to start the program (in this case emacs) with
>>
>>            pid = system("emacs", 1, "async").
>>
>> To check if the program is still running I could use 'system("ps")',
>> to close the program I could use 'system(["kill ", num2str(pid)])'.
>>
>> system("emacs", 1, "async") returns a PID to a new octave-process, and
>> not to the emacs-process, so I don't know the PID to the process to
>> kill.
> 
> you must 'exec' after fork, so the exec program (emacs) will substitute
> the forked one (octave).
> somethink like:
> 
> function pid = launch (command, args)
> 
> # pid = launch (command, args)
> #
> # this is similar to system(async), (fork/exec really)
> # but it first closes stdout and stderr to avoid spurious messages
> 
> if (nargin == 1 || nargin == 2)
> 
>         if (nargin == 1)
>                 args = "";
>         endif
> 
>         if (isstr (command))
>                 pid = fork ();
>                 fp = fopen("/dev/null","w+");
>                 if (pid == 0)
> #                       dup2 (fp, stdin);       # can't close this one...
> 
>                         dup2 (fp, stdout);
>                         dup2 (fp, stderr);
> #                       on_signal(2,"SIG_IGN","");
>                         if (exec (command, args) < 0)
>                                 error ("launch: unable to start process
> `%s'", c
> ommand);
>                                 exit (0);
>                         endif
>                 else
>                         fclose(fp);
>                         return;
>                 endif
>         else
>                 error ("launch: file name must be a string");
>         endif
> else
>         usage ("launch (command, args)");
> endif
> 
> endfunction



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