The Scala way to use one actor per socket connection

Question

I am wondering how it is possible to avoid one socket connection pr. thread in Scala. I have thought a lot about it, but I always end up with some code which is listening for incoming data for each client connection.

The problem is that I want to develop an application which should simultanously handle perhaps a couple of thousand connections. However I will of course not want to create a thread for each connection because of the lack of scalability and context switching.

What would be the "right" way to do this. In my world it should be possible to have one actor for each connection without the need to block one thread per actor.

Answer 1

I have an application that mixes actors with non-blocking sockets (i.e. NIO). The way I have done this is to have a dedicated IO thread, which sends messages to actors (in much the same way it would delegate work to a thread pool in a Java system) using the reactor pattern.

Obviously using the old blocking sockets, you are restricted to one thread per connection. And actor could handle this but of course this places a restriction on the number of connections which can be handled simultaneously.

In the case of a single IO thread, this is a bottleneck in theory but not much in practice (in our observations) as the IO thread is doing computationally non-intensive work. There are plenty of good discussions to be found on the NIO reactor pattern.

Answer 2

In the book "Programming Scala" the authors used a library called naggati which provides a framework that combines NIO and actors, http://programming-scala.labs.oreilly.com/ch09.html.