Re: multiple process calls from GTK

[Neil Hodge <neh attbi com>]

German:

On Fri, 2003-01-10 at 14:47, 447158 celes unizar es wrote:
> Hello,
>
>   I am developing an application in GTK+1.2 and my problem is that I want to
> execute two processes that communicate between them and then return their
> output.
>
>   First, I've got the problem of calling both processes at the same time, as I
> don't know how to do it (I know I can use the system() system call to execute
> something in a shell, but I don't know if it works for 2 programs...).
>
>   Another problem I have is that it would be great to process the information of
> the processes as it is generated (via standard output or another descriptor),
> but I don't know how to do it at the same time that these processes are
> executed.
>
>   I also would like to be able to stop them whenever a user could think it
> necessary, so my GTK application should be active while these processes are
> executing...
>
>   You see, concurrency and more concurrency... any help is wellcome!

Check out this post, made on this list on 2002-12-10.

################################################################################

           From: 
Havoc Pennington
<hp redhat com>
             To: 
German Poo
Caaman~o
<gpoo ubiobio cl>
             Cc: 
gtk-app-devel-list gnome org
        Subject: 
Re: The right way
to get the ouput
from a pipe into a
widget
           Date: 
Tue, 10 Dec 2002
18:10:06 -0500

On Tue, Dec 10, 2002 at 07:21:54PM -0300, German Poo Caaman~o wrote:
> I'm trying to connect the ouput from programs like ping and
> traceroute and show its results into some GTK widgets.  
> So, I use pipe, fork and exec.

Use g_spawn_async_with_pipes() instead, it'll immediately make this a
lot simpler.
 
> I'd appreaciatte any hint or idea about what I missing,
> or if my thought are right or wrong.

What you want to do is:

 - create the child process with g_spawn_async_with_pipes()
   creating a pipe on the child's stdout/stderr
 - use g_io_add_watch() to add a callback to be invoked 
   when there is input on the pipe (G_IO_IN)
 - when there's input, do a single call to read()
   and write the data that you read to the text view. 
   Don't read() twice, or you may block. (Unless you set the 
   pipe nonblocking)
 - when you get G_IO_HUP or G_IO_ERR passed to your IO watch 
   callback, the child process will have exited, so you want 
   to close your end of the pipe, and remove the IO watch.

Havoc

################################################################################

That sounds about like what you are looking for.  I also need to do this
for something I am working on; I just have not gotten to it yet, but
from what Havoc described, it does not seem that it would be too
difficult.

Neil