Channels as a Communication Primitive

Channels are useful when different coroutines need to communicate with each other. They guarantee no conflicts (i.e., no problem with the shared state) and fairness.

To see them in action, imagine that different baristas are making coffees. Each barista should be a separate coroutine working independently. Different coffee types take different amounts of time to prepare, but we want to handle orders in the order they appear. The easiest way to solve this problem is by sending both the orders and the resulting coffees in channels. A barista can be defined using the produce builder.