Processing data under load with GenServer (gen_server)

Question

I am testing the following pattern in a GenServer:

  def handle_info({:tcp, _, data}, s) do
    # IO.puts "\nrx: \n#{Base.encode16(data)}\n"

    extra = _proc_data(<<s.extra::binary, data::binary>>)

    :inet.setopts(s.socket, active: :once)

    {:noreply, %{s | extra: extra}}
  end

There is a problem when data comes in fast, and i'm unable to update state before :inet.setopts(s.socket, active: :once) releases new data

Must {:noreply, %{s | extra: extra}} be the last line for handle_info, or can I perform the :inet.setopts(s.socket, active: :once) last?

Is there a better way to do this?

Answer 1

One technique I've used in the past is to send the data to another GenServer for processing. This would allow the current process to call :inet.setopts(s.socket, active: :once) faster.

def handle_info({:tcp, _, data}, s) do
    # IO.puts "\nrx: \n#{Base.encode16(data)}\n"

    GenServer.cast(s.processor, {:data, data})

    :inet.setopts(s.socket, active: :once)

    {:noreply, s}
end

Processor:

defmodule DataProcessor do
  use GenServer

  def start_link(opts), do: GenServer.start_link(__MODULE__, [], opts)

  def init(_), do: {:ok, %{}}

  def handle_cast({:data, data}, state) do
    extra = _proc_data(s.extra <> data)    
    {:noreply, %{state| extra: extra}}
  end

  defp _proc_data(data) do
    ...
  end
end