[EMAIL PROTECTED] writes:
> First: Sorry for my long mail.
>
> In a program I wrote I start at the leaf and delete nodes (maybe) down
> to the root (depends on the node data). So it happend that at the end of
> my subroutine when I destroy the tree, I deleted the root node twice
> which could result (glib-1.2.7 or glib-1.2.8, gcc 2.95.2, SuSE 6.4) that
> my Window Manager gets killed.
My guess is that either that your stack size limit is very big or
you are tight on memory - in either case, the problem is that your
bug puts GTK+ into an infinite recursion.
> The error can be reproduced by the following program:
> <----------------- SNIPE ------------------------->
> #include <glib.h>
> int main(int argc, char** argv){
> GNode * root=NULL;
> GNode * tree=NULL;
> gint * data;
>
> data = g_new(gint,1);
> *data = 1;
>
> root = g_node_new(data);
> g_print("root : %d\n",(gint)* (gpointer *)(root->data));
>
> data = g_new(gint,1);
> *data = 2;
> tree = g_node_append_data(root,data);
> g_print("1st sibling: %d\n",(gint)* (gpointer *)tree->data);
>
> data = g_new(gint,1);
> *data = 3;
> tree = g_node_append_data(root,data);
> g_print("2nd sibling: %d\n",(gint)* (gpointer *)tree->data);
>
> data = g_new(gint,1);
> *data = 3;
> tree = g_node_append_data(tree,data);
> g_print("1st node of 2nd sibling: %d\n",(gint)* (gpointer
> *)tree->data);
>
> g_node_destroy(root);
> g_node_destroy(root);
[...]
> <----------------------SNIPE--------------------->
> So - It is probably bad programming style to delete the root node twice,
> but if glib could crash under such circumstances a user session....
It certainly is not "bad programming style", it is a plain old bug.
You cannot free a node twice, period.
> If glib is changed according to my suggestion there is still an other
> problem. If the root node is destroyed twice there are two copies of the
> root node memory adresse in the gnodes 'current_allocator' data
> structure. If later two new GNodes are fetched (g_node_new), you get
> twice the same memory adresse.
Freeing the same piece of memory twice is a bug, no matter whether
it is a list node, a tree node, a malloc()'ed block...
What your patch does is substitutes confusing slow corruption for an
immediate crash.
I've had to debug multiply freed list nodes a few times and it isn't
at all fun, since you eventually end up with a list node that is used
twice, and you get weird bugs that are completely unrelated to the
source of the problem.
(However, we are going to add a --enable-gc-friendly configuration
option to GLib which clears all sorts of freed memory, so that will
be a bit like your patch.)
Regards,
Owen
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