Listener

1. 0.85us per event, or 0.85 second for 1 millions of events
2. 15 times faster than boost::signals
3. 5 times faster than Qt Signal/Slot

It can be noted that the use of ListenerForEvent<E> is 5 times slower than using a classical Listener, since a special filter is used, and that a new pure virtual method is added.