Re: About-me-password backend

[Darren Kenny <Darren Kenny Sun COM>]

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
>
>
> _______________________________________________
> desktop-devel-list mailing list
> desktop-devel-list gnome org
> http://mail.gnome.org/mailman/listinfo/desktop-devel-list