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.

Add conditional_child to your list of dependencies:

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

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.

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

conditional_child source code is released under Apache License 2.0.

Check NOTICE and LICENSE files for more information.