arkgil / events Goto Github PK

This is just a wild idea, but could provide a very powerful and flexible API.

ETS allows making "standalone" match specs created with :ets.match_spec_compile/1 and executed with :ets.match_spec_run/2 - this is used by DETS for executing match specs and for example by the Version module for matching version requirements. Match specs are pretty efficient as they are executed on an internal small VM that runs inside BEAM itself, called PAM (Yo, Dawg).

I could imagine an API that allows you to subscribe with a match spec to events and would allow you to filter and possibly transform them before they would be delivered to you, reducing the amount of flying messages at the cost of extra work for the sender.

For example, here's a simple API for a PubSub based on elixir's Registry and this idea:

defmodule RegistryPubSub do
  def child_spec(opts) do
    Registry.child_spec(Keyword.merge(opts, keys: :duplicate))
  end

  def subscribe_match_spec(name, channel, spec) do
    Registry.register(name, channel, :ets.match_spec_compile(spec))
  end

  def publish(name, channel, events) do
    Registry.dispatch(name, channel, fn entries ->
      for {pid, spec} <- entries, event <- :ets.match_spec_run(events, spec), do: send(pid, event)
      :ok
    end)
  end
end

With some macro magic, I could imagine an API like:

require RegistryPubSub
RegistryPubSub.subscribe(MyServer, "foo_channel") do
  {:created, topic, _details} -> {:created, topic}
  {:deleted, %{name: name}} -> {:deleted, name}
end

I haven't evaluated the performance of this solution in practice, but I think it's very promising and allows for filtering events at the producer instead of filtering them at the receiver with a very powerful mechanism - basically almost all of pattern matching, since match specs are almost like making patterns first class citizens.