The problem with using stash is explained at https://groups.google.com/d/msg/akka-dev/IA7EwTx2DDE/vg8c68jN_kAJ which is a general problem when using a stash (regardless how it is optimized). To overcome this problem, you need a mechanism to explicitly request the next command from a queue, which is supported by `CommandQueue`. 

I was also experimenting with a variant of `PeekMailbox` but the problem here is that it interferes with the processor stash of `Processor` and the user stash. So I ended up with `CommandQueue`.