The EVM routes differently based on a few factors. Based on my knowledge:

1. A message sent immediately activates the receiving process if no contention.
2. A message is queued in its mailbox if the process is busy otherwise.
3. If the process is ‘too’ busy then not only is the message queued but the sending process is also ‘slept’ for some-odd reductions to act as a throttle mechanism, this time increases the more busy the receiving process is.
4. Or if the message is going over the network it is just blasted out and ‘forgotten’.

These are not things you should really think about 99% of the time though. If you want a specific routing strategy then you can add another actor/process between the senders/receivers to do that instead, but that is rarely ever done except in very specific situations.

The best pattern is of course just OTP itself.

Thanks for clarification! OTP is fantastic, just wanted to have some more control on message passing. This makes implementing things like custom load balancing easier. I guess that might be good idea for 3-rd party routing library. Probably I will try to port something that they have in Akka.

Thanks again

More libraries are always useful!

The only real in-use routing libraries I’ve seen just implement priority messages, so higher priority ones are handled before lower priority, regardless of arrival time. It is pretty easy to implement that one, the others you mentioned would not be hard either.