[Pharo-users] Acquiring lock, releasing in callback

Hello Dear Pharo users, threads and co. are giving me headaches :-) I wanted to ask for advice... What do I use in Pharo to prevent more than one thread entering a region, but "releasing" the exclusivity in another block/callback? For example, let's suppose there is an hypothetical class "Lock" that does that. lock acquire. longOperation performWhenFinished: [ callback code ... lock release ]. ... rest of the program ... Is there something like that? Or do I have to simulate it with something else? (Semaphore?) I am aware or Monitor/Mutex critical:, but I am not sure I can use it in my case. Thanks in advance, Sebastian