You make a very important point here. When you're creating a very high-throughput network server, you want to use as little Reactor and proactor I/O makes it v

You make a very important point here. When you're creating a very high-throughput network server, you want to use as little Reactor and proactor I/O makes it very easy to reason about execution order and more importantly memory usage. This kind of code usually gets written in C (or at the very best C++), and minimum memory usage per-socket is carefully planned. Co-routine context and and green thread stack size can be tweaked and optimized sometimes, but if you want to have precise control over memory allocated per-connection, reactor/proactor is hard to beat. Besides, to be 100% honest, C and C++ just doesn't have native support for any other concurrency model. That's probably the main reason why Node.js was designed to use callbacks. I'm pretty sure it would use generators or async functions if it was designed today.