poolboy_demo.ex

defmodule HttpRequester do
  use GenServer.Behaviour

  def start_link(_) do
    :gen_server.start_link(__MODULE__, nil, [])
  end

  def fetch(server, url) do
    :gen_server.cast(server, {:fetch, url})
  end

  def init(_) do
    {:ok, nil}
  end

  def handle_cast({:fetch, url}, state) do
    IO.puts "fetching #{url}"
    :timer.sleep 5000
    IO.puts "fetched #{url}"

    {:noreply, state}
  end
end



defmodule PoolboyDemo do
  def run do
    {:ok, pool} = :poolboy.start_link(
      [worker_module: HttpRequester, size: 5, max_overflow: 0]
    )

    Enum.each(1..20, fn(n) ->
      :poolboy.transaction(pool, fn(http_requester_pid) ->
        HttpRequester.fetch(http_requester_pid, "url #{n}")
      end)
    end)
  end
end