Migrating to dynamic supervisor

[laiboonh]

I am trying to address this warning in my repo
warning: :simple_one_for_one strategy is deprecated, please use DynamicSupervisor instead

I have updated all deps as recommended by some online solutions.

I have tried to migrate to using DynamicSupervisor but 3 problems:

1. i still see the warning
2. this does not do what i was doing initially whereby My.ChildProcess is started when application starts
3. instead of one supervisor now i had a supervisor that starts a dynamic supervisor that starts My.ChildProcess??? Why do i need to do this?

defmodule My.Application do
  use Application

  @impl true
  def start(_type, _args) do
    children = [
      {DynamicSupervisor, strategy: :one_for_one, name: My.DynamicSupervisor}
    ]

    Supervisor.start_link(children, strategy: :one_for_one)
  end
end

defmodule My.DynamicSupervisor do
  use DynamicSupervisor

  def start_link(init_arg) do
    DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
  end

  def start_child() do
    spec = %{id: My.ChildProcess, start: {My.ChildProcess, :start_link, [[]]}}
    DynamicSupervisor.start_child(__MODULE__, spec)
  end

  @impl true
  def init(init_arg) do
    DynamicSupervisor.init(
      strategy: :one_for_one,
      extra_arguments: [init_arg]
    )
  end
end

[kokolegorille]

I don’t have the same setup… and naming your dynamic supervisor My.DynamicSupervisor is asking for trouble (when using aliases for example)

Not the same syntax in the application, i just use

children = [
My.WorkerSup
]

Not the same child_spec, and I put it in the worker, not in supervisor. Example…

  def child_spec(args) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, args},
      restart: :transient,
      type: :worker
    }
  end

and I start children like this

  def start_child(args \\ %{}) do
    DynamicSupervisor.start_child(__MODULE__, {Worker, [args]})
  end

I am using Registry to name dynamic workers.

1. Are You sure You don’t have a dependency using simple_one_for_one?
2. Dynamic workers are meant to start on demand, why do You need to start it on boot?
3. Supervisor may have different strategies, and supervision tree is a tree that can be deep, with multiple levels of supervisors.

You should show your worker.

[laiboonh]

Answering your questions below

@kokolegorille

• Are You sure You don’t have a dependency using simple_one_for_one?
  Beginner here. I am not sure how can i check for that but my dependencies are

defp deps do
    [
      {:tesla, "~> 1.3"},
      {:hackney, "~> 1.16"},
      {:jason, "~> 1.2"},
      {:telemetry, "~> 0.4"},
      {:decimal, "~> 1.0"},
      {:ecto, "~> 3.3"},
      {:bypass, "~> 1.0", only: [:test]},
      {:excoveralls, "~> 0.12", only: :test},
      {:mix_audit, "~> 0.1", only: [:dev, :test], runtime: false},
      {:dialyxir, "~> 1.0", only: [:dev, :test], runtime: false},
      {:credo, "~> 1.5.0", only: [:dev, :test], runtime: false},
      {:ex_doc, "~> 0.21", only: :dev, runtime: false}
    ]
  end

Other than this my repo itself does not use :simple_one_for_one

• Dynamic workers are meant to start on demand, why do You need to start it on boot?
  I am trying to address the warning and the warning seems to be telling me to use DynamicSupervisor instead of Supervisor. Hence i am perplexed. It seems that to address the warning i have to substitue what i have now with something that does not serve the same purpose???
• Supervisor may have different strategies, and supervision tree is a tree that can be deep, with multiple levels of supervisors.
  Yes i know this but for my simple use case i thought a simple supervisor and one child process will suffice.