[blaforge]

For another perspective, you should take a look at JActor. https://github.com/laforge49/JActor

JActor is a high-throughput JAva actor framework capable of delivering up to 200 million messages per second on an i7. It achieves this by operating synchronously whenever it can.

The main innovation here is what I call commandeering, which allows an actor to process the message sent to another actor in the same thread--so long as the target thread is idle.