Registry

Register arbitrary PID

defmodule RegistryTest do
  def init() do
    Registry.start_link(
      keys: :duplicate,
      name: Registry.PubSubTest,
      partitions: System.schedulers_online()
    )
  end

  def subscribe_pid(pid) do
    # The third argument of `register` allows any arbitrary data, including a pid!
    {:ok, _} = Registry.register(Registry.PubSubTest, "hello", {pid, :other, "data"})
  end

  def send_message(message) do
    Registry.dispatch(Registry.PubSubTest, "hello", fn entries ->
      # Then you can just pull the pid out as the "subscriber" pid and send to it!
      for {_, {subscriber_pid, _other, _data}} <- entries, do: send(subscriber_pid, message)
    end)

    :ok
  end
end

pid1 =
  spawn(fn ->
    receive do
      :hello -> IO.puts("world")
    end
  end)

pid2 =
  spawn(fn ->
    receive do
      :hello -> IO.puts("ocean")
    end
  end)

pid3 =
  spawn(fn ->
    receive do
      :hello -> IO.puts("sky")
    end
  end)

RegistryTest.init()

RegistryTest.subscribe_pid(pid1)
RegistryTest.subscribe_pid(pid2)
RegistryTest.subscribe_pid(pid3)

RegistryTest.send_message(:hello)