Conditional Child

A wrapper for starting and stopping a child process in runtime, based on periodic checks.

A common use case is to start and stop processes when feature flags are toggled, but any condition can be used.

Installation

Add conditional_child to your list of dependencies:

def deps do
  [{:conditional_child, "~> 0.1"}]
end

How to use

Suppose you have a static Demo.Worker child in your application supervision tree:

defmodule Demo.Application do
  @moduledoc false

  use Application

  @impl true
  def start(_type, _args) do
    children = [
      Demo.Worker
    ]

    opts = [strategy: :one_for_one, name: Demo.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

To make it conditional, just wrap your child definition into a ConditionalChild process, passing start_if and child options, like in the diff below:

-      Demo.Worker
+      {ConditionalChild, child: Demo.Worker, start_if: fn -> your_condition() end}

Becoming:

defmodule Demo.Application do
  @moduledoc false

  use Application

  @impl true
  def start(_type, _args) do
    children = [
      {ConditionalChild, child: Demo.Worker, start_if: fn -> your_condition() end}
    ]

    opts = [strategy: :one_for_one, name: Demo.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

During initialization, ConditionalChild will execute start_if and only start the child process if it evaluates to true.

After that, it will execute start_if every second, and start/stop the process based on the result. The check interval can be changed if desired.

For more details, see ConditionalChild.

Code of Conduct

This project Contributor Covenant version 2.1. Check CODE_OF_CONDUCT.md file for more information.

License

conditional_child source code is released under Apache License 2.0.

Check NOTICE and LICENSE files for more information.