Created attachment 79966 [details]
[PATCH] Use GOnce for interface type registration

In certain cases, randomly, udisksd was failing with the following messages:

> (udisksd:10020): GLib-GObject-WARNING **: cannot register existing type `PolkitSubject'
> (udisksd:10020): GLib-GObject-CRITICAL **: g_type_interface_add_prerequisite: assertion `G_TYPE_IS_INTERFACE (interface_type)' failed
> (udisksd:10020): GLib-GObject-WARNING **: invalid cast from `PolkitSystemBusName' to `<invalid>'
> (udisksd:10020): GLib-GObject-WARNING **: cannot register existing type `PolkitSubject'
> (udisksd:10020): GLib-GObject-WARNING **: cannot register existing type `PolkitSubject'
> (udisksd:10020): GLib-GObject-CRITICAL **: g_type_interface_add_prerequisite: assertion `G_TYPE_IS_INTERFACE (interface_type)' failed
> (udisksd:10020): GLib-GObject-CRITICAL **: g_type_interface_add_prerequisite: assertion `G_TYPE_IS_INTERFACE (interface_type)' failed
> ** (udisksd:10020): CRITICAL **: polkit_authority_check_authorization_sync: assertion `POLKIT_IS_SUBJECT (subject)' failed
> ** (udisksd:10020): CRITICAL **: polkit_authority_check_authorization_sync: assertion `POLKIT_IS_SUBJECT (subject)' failed

Further debugging showed missing locking in polkit_subject_get_type() and potential race explaining the first GObject warning.

The attached patch makes the type registration use modern conventions with GOnce.