So here’s something I’ve been puzzling over. We have the result of Task.Supervisor.async_stream_nolink(Sup, [], &foo/1) piping into Enum.flat_map. I think my specific question would pertain to any use of the async_stream family.

I understand if I pass ordered: true to async_stream_nolink the results will feed into Enum.flat_map in order, and if I pass ordered: false they will feed in in the order the spawned processes complete.

Behind the scenes, what is happening to these processes spawned by async_stream when ordered is true or false? My assumption was that, regardless of what I pass for the ordered option, all tasks will need to complete before Enum.flat_map begins doing work. So in either case, things will need to buffer.

Is that true? In this specific scenario, is there any difference in terms of computation, memory usage, or process lifetime when I pass ordered: true or false?

We previously were using ordered: false, but recently have a need for ordered: true, and we’re trying to figure out if there are any consequences related to computation speed or memory.

I’ve walked through the Elixir codebase and docs a fair amount trying to find an answer but didn’t manage to piece it together myself.

I also know this is kind of a hard question to express, so I can certainly try to clarify or rephrase