It never stops the world for full heap collection, but there is a synchronization point where all threads have to check in. This is the only thing required, so

It never stops the world for full heap collection, but there is a synchronization point where all threads have to check in. This is the only thing required, so you have GC pauses, just really, really small ones. That's why I said, that practically, GC pauses are no longer relevant.