> Does anyone know how the PyPy implementation differs
It differs significantly in that the whole interpreter works under STM, it's not just an API.
> Is it just laying the groundwork for leveraging hardware transactional memory support, or is the thesis that this will eventually become usable directly?
It's a development project at this point (you can — and should — check the backlog on pypy's blog), but the goal is to have it usable directly and pave the groundwork for HTM/
It differs significantly in that the whole interpreter works under STM, it's not just an API.
> Is it just laying the groundwork for leveraging hardware transactional memory support, or is the thesis that this will eventually become usable directly?
It's a development project at this point (you can — and should — check the backlog on pypy's blog), but the goal is to have it usable directly and pave the groundwork for HTM/