how can i know how many slots connected to a signal?

[yj_yulin]

Emiting a signal is very cheap. It's a simple function call. If there are no slots connected, nothing more will happen.

signals:
void a_happend(Tsomeobject * obj, int x, int y);

yeah, though signal is cheap, the object need to create(Tsomeobject * obj) maybe not.

and my situation also relate to the object management,thus if i can know there is no slots connected to the signal, it can reduce more work.

thanks for all involved, and especially to jpn.