Re: About-me-password backend

["Gustavo J. A. M. Carneiro" <gjc inescporto pt>]

  Note that glib already has g_child_watch_add, which is a lot simpler
and safer to use than signal().  In the callback you can see what status
the child returned and if it received a signal instead.

  Regards.

On Ter, 2006-04-11 at 09:42 +0100, Darren Kenny wrote:
> Hi Johannes,
> 
> The most correct way to handle the status of a child process is to catch 
> the unix signal 18 - SIGCHLD - this should be fired by the OS (assuming 
> unix based) should the fork/execed process exit.
> 
> So you need to set up a signal handler for SIGCHLD, before you enter the 
> processing loop, and have this signal handler store the pid of the 
> passwd process so that later you can check if this is the one that exited.
> 
> Meanwhile, a loop with a  read on an file descriptor (e.g. waiting for 
> the "Password: " string from passwd) will be interrupted due to the 
> SIGCHLD and return -1, and errno will be set to EINTR - if you check for 
> these conditions and then call the child_exited call then you should 
> know if passwd exited.
> 
> For example:
> 
>     signal( SIGCHLD, reapChildProcess );
>     while ( ! done ) {
>         if (read(...) < 0 ) {
>             if ( errno == EINTR && child_exitied( passwd_pid) == TRUE ) {
>                 done = TRUE; /* or whatever you want to do to exit gracefully */
>                 continue; /* or break if you want to force exit of the loop */
>             }
>         }
>         /* normal processing */
>     }
>       
> 
> (BTW, I'm assuming you don't have multiple processes forked, if you do 
> you probably need to store the last N processed exited for check to work).
> 
> There should be loads of examples of this type of thing on the net...
> 
> Darren.
> 
> Johannes H. Jensen wrote:
> > Dear almighty GNOME hackers, I'm in need of some pointers!
> >
> > I'm currently hacking on the about-me password dialog (see #321567), 
> > which is spawning /usr/bin/passwd to authenticate and change the 
> > password. In the new dialog, I'm dividing the process in two, so that 
> > the user has to authenticate with his current password first (which 
> > spawns passwd to verify). If passwd doesn't complain and prompts for 
> > the new password, he can enter his new password, retype it and hit 
> > "Change password". When he hits the button, some time has elapsed 
> > since he first authenticated (and thus passwd was spawned).
> >
> > Now my question is, what happens if passwd suddenly dies during that 
> > time period? Is it likely it will? If so, what's the best way to 
> > periodically(?) ensure that the process is running? Check every n 
> > seconds with waitpid() in the main loop? As far as I can see, this is 
> > how it's done in the current version - wait_child() is called every 4 
> > seconds to check what the backend is doing...
> >
> > Any pointers greatly appreciated :)
> >
> > Btw, a more detailed mockup of the program/process flow can be found 
> > at http://joh.deworks.net/password-dialog/GnomeAboutMePassword.html
> >
> > Best regards,
> >
> > Johannes H. Jensen
> > deworks
> >
> >
> > _______________________________________________
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> > http://mail.gnome.org/mailman/listinfo/desktop-devel-list
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-- 
Gustavo J. A. M. Carneiro
<gjc inescporto pt> <gustavo users sourceforge net>
The universe is always one step beyond logic.