GenStage ProducerConsumerSupervisor?

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Based on my GenStage experiments and reading the ConsumerSupervisor documentation here are my thoughts:

  • ConsumerSupervisor is a Supervisor process which creates a child process for each event that it receives. In general Supervisors are designed to be as simple as possible so that they can focus on one thing: “supervising child processes” (while not taking on any additional responsibility which may cause them to crash) - this one just happens to dynamically create children for any events received. By this nature the ConsumerSupervisor can only really be a Consumer in a GenStage scenario as a supervisor typically doesn’t collect and manage results from its children.

  • Your particular [A] -> [B(1, 2, 3, 4, 5, ...)] -> [C] scenario could be realized with C as a Producer (if there is a (producer-) consumer D). Essentially the children of the ConsumerSupervisor would simply deliver their result to C via GenStage.cast/2 or GenStage.call/3 - i.e. flow to C would be entirely governed by the :min_demand, :max_demand settings on B, the ConsumerProducer.

  • The documentation of init is strange to say the least. There is a ConsumerSupervisor.init/1 callback that is analogous to Supervisor.init/1 - so I would expect ConsumerSupervisor.init/1 function to be analogous to Supervisor.init/2. The text of the ConsumerSupervisor.init/2 function seems very similar to the text of the Genstage.init/2 callback - so I suspect a copy/paste error. The ConsumerSupervisor.init/1 function code simply prepares a tuple containing the supervisor flags and child specifications.

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