[Kde-bindings] debugging a korundum program after a crash

[Stefano Crocco]

Alle Monday 30 March 2009, Richard Dale ha scritto:
> On Monday 30 March 2009 10:38:57 Stefano Crocco wrote:
> > My korundum4 program is randomly crashing. By 'crashing', I don't mean
> > it's raising an exception which isn't caught, but that it's crashing at
> > the C++ level. This could mean I just found a bug in qtruby or korundum
> > but it's much more likely that it simply means my program is doing
> > something it shouldn't.
> >
> > If my program raised an exception, I could simply look at the line where
> > the exception was raised and from there follow the program flow and try
> > to understand what's wrong. Of course, with a C++-level crash, I can't do
> > that, since the backtrace only contains calls to qt/kde/smoke/qtruby/ruby
> > internal functions.
> >
> > Do you have any advice on how to proceed?
>
> Post the C++ backtrace on the mailing list in case that gives a clue about
> the cause. Try to make the smallest program that is possible that
> reproduces the crash. Does it still crash if you turn off garbage
> collection with 'GC.disable'?

Thanks for your answer. I tried disabling garbage collection, but the errors 
persisted. As for making the smallest program that reproduces the crash, this 
is going to be difficult, for two reasons: first, the crashes are random, so 
that the same operation sometimes works and sometimes crashes; second I think 
the bugs I see seem to be caused by the interaction among several pieces of my 
application, so I don't think I can make a smaller program. At any rate, I'll 
post the backtrace as soon as I get the crash again.

However, I think I found a way to at least find out were the crash happens: 
since I know which actions can lead to a crash, I use set_trace_func just 
before those points, so that I can at least see where the crash happens.

The first results haven't as yet given me any clue as to the cause of the 
crashes. However, I've found an exception being raised by the following code 
(simplified):

class Document < Qt::Object

  def method_missing name, *args, &blk
    begin super
    rescue NoMethodError, NameError
      @doc.send name, *args, &blk
    end
  end

  ...

end

What I'm trying to do here is to create a wrapper around an instance of 
KTextEditor::Document (stored in @doc). The idea is that, if a method isn't 
defined in Document, it should forward it to @doc. Since I know that qtruby 
uses method_missing itself, I first called the Qt::Object implementation of 
method_missing and only if it fails I pass the method call to @doc. Do you 
known whether what I'm doing here is safe? I admit I don't like it at all, and 
I'd like to replace it with something else (most likely using the Forwardable 
module), but I've never done that because of the huge number of methods in 
KTextEditor::Document.

Thanks again

Stefano