Yes - Stoning in certain cultures, cultures that practices sharia, they follow rules, and like you said, continue it until 'the sinner' dies. I read somewhere it is very important that, “… no stone should be thrown that should kill with the first or second blow, or so small as a pebble to do no injury to the condemned.
Having problems confirming that rule, but stoning isnt a precise science(?), and when we talk about stoning here i guess we are thinking of capital punishment in the sharia system. But stoning has been reported from Yodok concentration camp in north korea and im not quite sure if death penalty is the motive there, i suspect the torturing element is the key factor there.
They made a documentary about that camp -->
http://www.imdb.com/title/tt1266731/
Anyway, i have a feeling that im deviating from topic here, namely torture scenes in movies :o