On Fri, 2003-07-04 at 04:08, Dave Benson wrote:
> Hello,
>
> Almost all get_type() functions contain code
> like
>
> GType
> whatever_get_type (void)
> {
> static GType object_type = 0;
>
> if (!object_type)
> {
> static const GTypeInfo object_info =
> { ... };
>
> object_type = g_type_register_static (G_TYPE_OBJECT, "Whatever", &object_info, 0);
> }
>
> return object_type;
> }
>
> Is this thread-safe? I cannot see any guards in
> g_type_register_static that prevent a second type-node from
> being allocated in the obvious race condition
No, it's not thread safe. You could have two type nodes allocated
or the second call to check_type_name_I() could fail.
The fact that whatever_get_type() isn't thread safe if "whatever"
is gtk_, but it is a problem for functions in libgobject, like
g_closure_get_type().
A bug about this in bugzilla would be appreciated (I think we've
noted this before, but having it tracked officially would be
good). There are two relevant other bugs:
- To fix the above without a fairly big speed penalty, you need GOnce:
http://bugzilla.gnome.org/show_bug.cgi?id=69668
(The obvious fix, to make g_type_register_static() return the
already registered type is the dubiously safe "double checked
locking" idiom)
- Fixing this for object types doesn't do you much good without
also fixing:
http://bugzilla.gnome.org/show_bug.cgi?id=64764
What people do currently when using GObject in threaded applications
is to call g_type_class_ref (MY_TYPE_WHATEVER) for all their types
before creating the first thread.
Regards,
Owen
