Re: [patch] calling g_malloc & co via a vtable

[Sebastian Wilhelmi <wilhelmi ira uka de>]

Hej Alexander,

> Here is a patch that adds a vtable to g_malloc, g_malloc0, g_realloc and
> g_free. It also adds g_try_malloc and g_try_realloc (not guaranteed to
> return non-NULL).
> 
> Is any one interested? Any comments?

Yes: Don't do it.

What would you want to do with other malloc implementations?

1) Use different allocation strategies, memory locations etc: That seems to
be    a reasonable idea. However I doubt, that there are many applications for
   that, so it might be just as good to simply link against your own versions
   of malloc, free etc.
2) Implement an out-of-memory callback: What will happen? A g_list_.. function
   will call g_malloc, no memory is available, the callback is called, your
   code there decides to free a cache (being a GList), but the main GList   
   mutex will be locked. Bummer. In general the internal state will not be
   consistent during a call to malloc, so allowing other calls from there will
   be a nightmare.

For a longer discussion on that topic, please have a look at 

http://mail.gnome.org/archives/gtk-devel-list/2000-February/msg00076.html

> The memory check and profiling has got a lot of ifdefs in it. Since they
> are now in a vtable you could actually compile them in all the time. Or
> just rip them out and let the application do such stuff by themselves.

For that reason admittedly such a vector could be used, but I wouldn't like
that being exported.

> One thing that i'd like to add, which is pretty usefull in embedded
> systems is a memory pressure callback. It would be called when
> malloc() fails to let the developer try to free some memory (flushing
> caches etc). What do you think of this? It could be done by the user using
> a custom GAllocFunctions, but then Gtk+ and Glib couldn't use it.

Nono, I knew, that would finally be the reason for the callback... Don't.

BTW.: How do you implement realloc without knowing the previous allocated
size?

Hej då
Sebastian
-- 
Sebastian Wilhelmi                   |            här ovanför alla molnen
mailto:wilhelmi ira uka de           |     är himmlen så förunderligt blå
http://goethe.ira.uka.de/~wilhelmi   |