chan chan Foo seems like a cool trick, looking forward to use it in the code; thanks for the idea.

PS. I realize you present even better solution; still, first version seems like a thing nice enough to have in a toolbox

> Curious how others tackle such problems.

What do you think about the order preserving simplicity of Java?

  List<Input> inputs = ...;

  List<Output> results = inputs.parallelStream()
                             .map(this::processTask)
                             .collect(toList());