[pron]

Yes, but at the end of the day, underneath it all, you gotta have threads because that's what the hardware understands. Even if you use hardware interrupts to detect IO, you still need a plain old thread to handle it. The only difference between various languages and runtimes is how you distribute tasks among the threads. Some environments provide green threads that have a partial stack, but even they are handed off to a thread pool (or a single thread) for execution.

It's been found that if you employ only a single thread (that can run any number of tasks) you get a performance boost over using a larger threadpool under some conditions, but a single thread wouldn't let you scale by taking advantage of all processors.

[ithkuil]

I feel that the cause of misunderstanding lies in the fact that "thread" in this context is usually means "thread based IO", which means that when a thread issues a IO request it remains blocked until the IO request returns, leaving CPU time to other threads. All this regardless how many processors you have; it works perfectly fine with single processors.

Async IO is different, it's a different patter of access to IO and as such it's orthogonal to any threading or multiprocessing that's going on in order to actually do stuff in response to that IO.

> It's been found that if you employ only a single thread (that can run any number of tasks) you get a performance boost over using a larger threadpool under some conditions, but a single thread wouldn't let you scale by taking advantage of all processors.

Indeed. Nodejs solution to this problem is to have a cluster of nodejs processes and a dispatcher process on top. So multiprocessing is done the "old way".

[pron]

In that case, Java gives you both options: blocking IO and non-blocking, polling IO. Netty can use both, but most people use it with the non-blocking option. Experiments have shown that sometimes one is faster and sometimes the other.