I’ll say my impression from what I’ve seen is that there is excessive use of GenServer and it appears to be using those GenServers almost like objects. There is this post by Saša Jurić that explains why that approach isn’t so good. In addition to the excessive use of GenServer, I’d say that a project per GenServer seems excessive as well.
I don’t think everything in the video is horribly wrong though. The things that stand out to me as odd are the DirWalker which is implemented as a GenServer that produces a stream and the HashStore as it’s own GenServer. It’s odd to me that the DirWalker is implemented as a GenServer, when it could just as likely be implemented with Stream.resource/3 in a module with just functions. The problem being solved in the video is effectively a map > reduce > filter problem. So, I can imagine it being very reasonable to have multiple mappers, though it could very well be slower in this case. My implementation to this problem would likely have been:
def find_duplicate_in(tree) do
DirWalker.stream() # this wouldn't use a GenServer, why send a blocking request to another process?
|> Task.async_stream(&HashGenerator.process/1) # Why reinvent tasks?
#or |> Stream.map(&HashGenerator.process/1) # Concurrency could perform worse
|> Enum.group_by(&(&1.hash), &(&1.filename))
|> Enum.filter(fn
{_hash, files} when length(files) > 1 -> true
_ -> false
end)
end
