Re: [Perlpanel-devel] catching applet exceptions

[Moshe Kaminsky]

Hi,

* Gavin Brown <address@hidden> [12/07/04 14:57]:
> Moshe wrote:
> 
> > As I wrote in another mail, I think perlpanel has a problem with 
> > exceptions caused in the applets code.
> > Naturally, not all applets handle all exceptions that arise in their 
> > code. When such an exception happens, it crashes the whole panel. This 
> > is unfortunate, especially since there is always new applet code to 
> > test.
> 
> I think this is less of a problem for a "standard user", who will only
> use the applets that ship with PerlPanel.

Is that really the way you would like it to be? I thought there would be 
some web location where people could contribute their applets. Writing 
an applet is an easy task, probably many would be contributed by various 
people.

> It is my hope and aim that all
> the applets behave well regarding exceptions, so that such a user will
> never see one.

This might not be that easy. After all, it's interactive. It is 
certainly not the situation today.
> 
> As for those people testing new applet code, I hope they'd find the
> crashes annoying enough to fix the code :p
> 
> > I believe there is a way to solve it, but I don't know enough about 
> > gtk/glib to know for sure: As far as I understand, all applets are 
> > children of an hbox. What I thought is to put this hbox inside a 
> > Gtk2::EventBox. Now, this widget has a method set_above_child, which 
> > allows it (as I understand it) to get all signals (button clicks, etc.), 
> > instead of the hbox. This EventBox will then pass the signal to the hbox 
> > child inside an eval block, thus trapping exceptions that occur in the 
> > callbacks. In addition, all methods such as configure, 
> > get_default_config, etc. should also, of course, be called inside an 
> > eval.
> 
> I agree absolutely about the configure() and get_default_config() calls,
> and I will probably sort that out today.
> 
> As for the event box magic, I'm pretty sure that your proposal wouldn't
> reliably work, since an error be raised at any moment (due to a
> Glib::Timeout, or a thread or any other of the asynchronous ways that
> Perl can do stuff) and might not necessarily be captured by gtk2-perl's
> exception system.

I guess it won't cover all cases, but I think that typically you'll 
either have a signal or a timeout. For the timeouts, I think the 
simplest is to add a timeout method to PerlPanel::Applet, and ask applet 
writers to use it for timeouts. This will solve the exceptions problem, 
and will also give a slightly higher level layer above Glib. (By the 
way, is it true that applets are supposed to derive from 
PerlPanel::Applet?)

> 
> It's definitely something worth thinking about though. gnome-panel's
> approach is to run a lot of the applets as separate processes and use
> XEMBED, but I'm not a big fan of that technique, since it clutters up
> 'ps'.
> 
> > The only thing is, I don't know if it's possible to install a "universal 
> > callback" for all signals, and how can one pass the signal to another 
> > widget.
> 
> There is the 'event' signal, but I've never been able to do anything
> useful with it. Attaching a handler to it just seems to freeze the
> application.

I guess that actually, taking over a few signals, such as the button 
clicks and button strokes should be enough. Of course, if someone really 
wants to break the application, he probably can.
BTW, I think that the method that can be used for passing the signal to 
the child is Glib::Object->signal_emit (is there some searchable version 
of the glib/gtk docs?).

I've just stumbled upon the Glib::Signal manpage. It appears there is a 
builtin way of doing all of this, using Glib->install_exception_handler 
(at least that's how it reads to me). I wasn't able to get it to work, 
though.

Moshe

> 
> Gavin.
> 
> -- 
> Gavin Brown
> e: address@hidden
> w: http://jodrell.net/
> PGP/GPG key ID: 891D8FCA
> 
> 
> 
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    Moshe Kaminsky <address@hidden>
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