Thanks for the explanations Desdinova and MGlitch, I've understood

! it's not always easy for non english people to understand those technical posts.
Two questions but the first is the main :
1. I can imagine Sickle consumes battery if this "function" is always checking the tasks????
2. If I take 3 minutes to read a page, can Sickle think that the page has frozen? => I imagine that Sickle is like "nagios" : only some tasks are checked, so this "freeze" is not detected and it's the reason why there is no reboot...