Attempts registration of the application.
This is the point at which the application discovers if it is the primary instance or merely acting as a remote for an already-existing primary instance. This is implemented by attempting to acquire the application identifier as a unique bus name on the session bus using GDBus.
If there is no application ID or if g_application_non_unique was given, then this process will always become the primary instance.
Due to the internal architecture of GDBus, method calls can be dispatched at any time (even if a main loop is not running). For this reason, you must ensure that any object paths that you wish to register are registered before calling this function.
If the application has already been registered then true is returned with no work performed.
The startup signal is emitted if registration succeeds and this is the primary instance (including the non-unique case).
In the event of an error (such as
cancellable being cancelled, or a failure to connect to the session bus),
false is returned and throws is set appropriately.
Note: the return value of this function is not an indicator that this instance is or is not the primary instance of the application. See get_is_remote for that.
a Cancellable, or null
true if registration succeeded