Programming Elixir Process Overhead Demo

[KronicDeth]

@pragdave's Programming Elixir was the first Elixir book I read and I still use the Process Overhead demo with 1,000,000 processes to show off that new Elixir programmers shouldn't be worried about making Processes the way they would be with threads. Showing we can compile spawn/chain.ex and run it Chain.run(1_000_000) would be a good MVP target for us.

spawn/chain.ex

defmodule Chain do
  def counter(next_pid) do
    receive do
      n ->
        send next_pid, n + 1
    end
  end

  def create_processes(n) do
    last = Enum.reduce 1..n, self,
                       fn (_, send_to) ->
                         spawn(Chain, :counter, [send_to])
                       end

    send last, 0 # start the count by sending a zero to the last process

    receive do # and wait for the result to come back to us
      final_answer when is_integer(final_answer) ->
        "Result is #{inspect(final_answer)}"
    end
  end

  def run(n) do
    IO.puts inspect :timer.tc(Chain, :create_processes, [n])
  end
end

The book has the 1,000,000 processes run like this: elixir --erl "+P 1000000" -r chain.ex -e "Chain.run(1_000_000)".

• Compiler
  • Anonymous functions
  • [h | t]
  • Multiple Erlang Modules
• Runtime
  • receive
    • non-selective
    • selective
  • Status::Waiting (for when there is nothing to receive yet)
  • BIFs
    • +/2 (+/2 #63 as add_2)
    • <>/2 (used internally by Elixir interpolation)
    • is_integer/1 (Partial Term and :erlang implementation #21)
    • send/2 (:erlang.send/2 and !/2 infix operator #105)
    • spawn/3 (:erlang.spawn/3 #118)
      • Fixed module and function
    • :timer.tc (not a BIF, but uses these BIFs)
      • apply/2
      • convert_time_unit/3 (convert_time_unit/3 #22)
      • monotonic_time/0(:erlang.monotonic_time/0 #107)
    • IO.puts (dependencies)
    • Enum.reduce/3 (dependencies)
      • :lists.foldl/3 (dependencies)
        • is_function/2
      • inspect/1 (dependencies)
        • Inspect.Algebra
          • group/1
            • doc_group/2
          • to_doc/1
          • format/2
        • IO
          • iodata_to_binary/1
            • iolist_to_binary/1