gboolean g_signal_has_handler_pending ( GObject* instance, guint signal_id, GQuark detail, gboolean may_be_blocked )
Returns whether there are any handlers connected to
instance for the
given signal id and detail.
detail is 0 then it will only match handlers that were connected
without detail. If
detail is non-zero then it will match handlers
connected both without detail and with the given detail. This is
consistent with how a signal emitted with
detail would be delivered
to those handlers.
Since 2.46 this also checks for a non-default class closure being installed, as this is basically always what you want.
One example of when you might use this is when the arguments to the signal are difficult to compute. A class implementor may opt to not emit the signal if no one is attached anyway, thus saving the cost of building the arguments.