Re: Bug in GLib, libglade, libc??

["Samuel Cormier-Iijima" <sciyoshi gmail com>]

Hi,

First of all, this should really be better documented elsewhere, but
valgrind has some problems debugging and profiling multithreaded code
(such as Gtk/Glib). To get some more accurate results, try the
following:

G_SLICE=always-malloc G_DEBUG=gc-friendly valgrind -v --show-reachable "myapp"

Some more of these environment variables are documented here:
http://developer.gnome.org/doc/API/2.0/glib/glib-running.html

Also, if you're using lists and strings and such, you might want to
use the GLib API's instead of hand-rolling your own. Things such as
GSList, GList, and GString can make your life a lot easier, depending
on what you're doing.

Finally, you shouldn't be using g_free on GObjects (such as GtkWidgets
and *I think* the GladeXML). Rather, use gtk_widget_destroy or
g_object_unref. GLib uses reference counting so that you don't have to
worry too much about memory management.

If trying these things doesn't work, you can always post the code ;-)

Cheers,
Samuel

On 8/14/06, Fabricio Rocha <rocha_fabricio yahoo com br> wrote:
> Thank you very much, Yeti and Samuel, for your replies!
>
>         I really believe that there is something wrong in MY code, and not in
> libglade, nor libc, nor GTK, etc., that makes my program react so
> different every time I compile and run it. However, I still could not
> figure what exactly is wrong.
>
>         I have a suspicion from my lack of practice in C: a module of my
> program uses a structured type which must contain, as its last member, a
> dynamic list of strings, i.e., pointers to gchars (**list). Sometimes I
> need to fill only the first string, and sometimes I will need more than
> one string. So I suspect that each attempt to set a value for one of
> these pointers cause a serious corruption of other areas of the program,
> like the GTK stuff in memory. I have tried to assign values to this
> (these) pointers both with g_strdup and by creating a local, initialized
> array and assigning its address to the pointer. Neither worked. Do you
> think I should give each pointer a malloc'd space somewhere in memory,
> and then strcpy the value to this pointer?
>
>         By the way, I have read a lot of GDB and Valgrind docs, and still could
> not get anything from them. My application is one of those standard
> libglade apps with a main() function that only loads a main window from
> the XML and show it, and I really don´t understand some things from
> Valgrind:
>
>         - "Conditional jump or move depends on uninitialised values", which is
> by itself not so bad, according to Valgrind docs;
>
>         - "Syscall param write (buf) points to uninitialised byte(s)" in the
> lines which calls gtk_init(&argc, &argv) and gtk_init(); which, if I am
> right, is normal as there is nothing passed to the application in the
> command line;
>
>         - Various "Invalid read of size 4 (...) Address 0xxxxx is 24 bytes
> inside a block of size 25 alloc´d" caused by the line with
> "glade_xml_signal_autoconnect". Hey, what is wrong if an address is
> WITHIN the alloc´d block?? And look that, until now, there is *not* code
> of "myself", it is just what every libglade example tells!
>
>         - "Invalid free() / delete / delete[]" in the lines right after
> gtk_main(), where I try to g_free both the pointers to the loaded XML
> file and the main window widget. I have set breakpoints in GDB right
> before these lines and they HAD non-NULL values until here...
>
>         - The program finishes with surprising 141kB "possibly lost" and 931kB
> (!) "still reachable" memory leaks. I can´t figure out what exactly is
> causing such a memory waste -- the only thing the program does until now
> is loading and closing the main window and a dialog window! In
> GTK/libglade programming, could you point out which are the most common
> "to-check" things to avoid that?
>
>         Please, sorry for such a big post, but I hope you understand that, as
> Yeti said, I am really *trying* to debug the thing by myself, instead of
> just coming here and shout.... but until now I couldn´t really find any
> big clue with GDB, and, although Valgrind is really impressive, it does
> not tell much about *what* to do for newbies like me -- as a friend
> said, it is like going to a physician who says "hmm, it looks like you
> have fluid in your left lung", but does not tell you how it happened and
> what to do then...
>
> Thank you again and best regards to all!
>
> Fabricio Rocha
> Brasilia, Brasil
>
>
>
>
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