A wrapper for managing concurrent Erlport Python processes with ease.

Venomous is a wrapper around erlport python Ports, designed to simplify concurrent use. It focuses on dynamic extensibility, like spawning, reusing and killing processes on demand. Furthermore, unused processes get automatically killed by scheduled process which can be configured inside config.exs. Venomous core functions capture and handle :EXIT calls ensuring that all python process die with it and do not continue their execution.

Installation

Add :venomous to your list of dependencies in mix.exs:

def deps do
  [
    {:venomous, "~> 0.4.1"}
  ]
end

Getting Started

Check the documentation for more in-depth information.

For custom type conversion see the Handling Erlport API

By default the python modules to load are kept inside PYTHONPATH envvar. but I highly recommend setting them inside python_opts[:module_paths]

You can checkout examples here

Configure the SnakeManager options

config :venomous, :snake_manager, %{
  # Optional :erlport encoder/decoder for type conversion between elixir/python applied to all workers. The function may also include any :erlport callbacks from python api
  erlport_encoder: %{
    module: :my_encoder_module,
    func: :encode_my_snakes_please,
    args: []
  },
  # TTL whenever python process is inactive. Default: 15
  snake_ttl_minutes: 10,
  # Number of python workers that don't get cleared by SnakeManager when their TTL while inactive ends. Default: 10
  perpetual_workers: 1,
  # Interval for killing python processes past their ttl while inactive. Default: 60_000ms (1 min)
  cleaner_interval: 5_000,

  # Erlport python options
  python_opts: [
  module_paths: ["/path/to/my/modules", "/path/to/other/modules"], # List of paths to your python modules.
  cd: "/", # Change python's directory on spawn. Default is $PWD
  compressed: 0, # Can be set from 0-9. May affect performance. Read more on [Erlport documentation](http://erlport.org/docs/python.html#erlang-api)
  envvars: [SNAKE_VAR_ONE: "I'm a snake", SNAKE_VAR_TWO: "No, you are not"], # additional python process envvars
  packet_bytes: 4, # Size of erlport python packet. Default: 4 = max 4GB of data. Can also be set to 1 = 256 bytes or 2 = ? bytes if you are sure you won't be transfering a lot of data.
  python_executable: "/bin/python" # Change the path to python executable to use.
      ]
}

Configure the SnakeSupervisor and PetSnakeSupervisor (if needed) to start on application boot.

defmodule YourApp.Application do
  @moduledoc false

  use Application

  @doc false
  def start(_type, _args) do
    children = [
      {Venomous.SnakeSupervisor, [strategy: :one_for_one, max_restarts: 0, max_children: 50]},
      {Venomous.PetSnakeSupervisor, [strategy: :one_for_one, max_children: 10]} # not necessary
    ]
    opts = [strategy: :one_for_one, name: YourApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

Quickstart

Basic way to call python process

alias Venomous.SnakeArgs
import Venomous

timeout = 1_000
args = SnakeArgs.from_params(:builtins, :sum, [[0,1,2,3,4,5]])

case python(args, python_timeout: timeout) do
    {:retrieve_error, msg} -> "No Snakes? #{inspect(msg)}"
    %{error: :timeout} -> "We timed out..."
    sum -> assert sum == 15
end

# or just use python!/3 which waits for the available snake.
timeout = :infinity
assert python!(args, python_timeout: timeout) == 15

Concurrency and :EXIT signals

Venomous is designed with concurrency, as well as proper exits in mind.

alias Venomous.SnakeArgs
import Venomous

# Venomous can handle as much concurrent python as you've setup
# in your snake_manager configuration. However the python! will
# wait for any process to free up in case none are available.
args = SnakeArgs.from_params(:time, :sleep, [0.5])
Enum.map(1..100, fn _ -> 
    Task.async(fn ->
        python!(args)
    end)
end) |> Task.await_many(5_000)

# You can view the spawned and ready snakes using the list_alive_snakes() 
list_alive_snakes() |> dbg

alias Venomous.SnakeArgs
import Venomous

# Venomous kills the OS pid of the python process on :EXIT
# ensuring the process will not proceed with the execution further
Enum.map(1..200, fn _ ->
  {:ok, pid} =
    Task.start(fn ->
      SnakeArgs.from_params(:time, :sleep, [1000]) |> python!()
    end)

  pid
end)
|> Enum.each(fn pid ->
  Process.send_after(pid, {:EXIT, :snake_slithered_away}, 100)
end)

# We'll sleep to make sure all exits got sent.
Process.sleep(1_000)
assert list_alive_snakes() == []