asynchronous idiom / load balancing (30Hz -> 10Hz -> 30Hz)

[ethanrublee]

Need a way to easily encapsulate a user module so that it runs asynchronously and doesn't block.

[straszheim]

we considered an encapsulating module that contains a plasm and pushes an optional

[straszheim]

this usecase turns out to be similar to the realtime case: if the last 30Hz node is realtime, then it must understand that it may not get a result from the 1Hz node.

The motivation for the optional (instead of shared_ptr-to-null) is that it lets the type system know that "I might not get one of these" into the type system, which is not assumed to be the case for the generic shared_ptr argument.