It's true that Erlang has some capabilities of preemption, but now we're getting into an altogether more interesting range of details. Erlang is still essentia

It's true that Erlang has some capabilities of preemption, but now we're getting into an altogether more interesting range of details. Erlang is still essentially cooperative and not preemptive, if I've understood my reading. That means the BEAM VM is doing something very similar to the style of instrumentation Quasar is doing: it injects yields into your code at points it thinks are reasonable. This is not quite the same thing as true preemptive scheduling as OS-native threads do. Quasar could do this kind of safepoint injection as well, though afaik that's not currently a feature. Your definition of ponies and mine seems to diverge here, and that's fine :) I agree that true preemptibility is an even higher bar we can hold scheduling frameworks to. But it's also a very complicated area to get into, it's not completely without it's tradeoffs (full preemptibility pretty much gets us back to OS native threads, right? and there's very real performance reasons there's so much momentum away from that right now), and I also feel that I can get a lot done with green threads without these features. Maybe we'll see a growing swing towards safepoint injection for psuedopreemptibility -- I'm just making words up at this point, as far as I know; if there's a better existing terminology for these shades of grey I'd love a link -- in the coming years. I don't know where I place my bets on that, yet. EDIT: this also appears to have been discussed before at https://news.ycombinator.com/item?id=7962838 https://news.ycombinator.com/item?id=7962838