Heavy work when starting DinamicSupervisor

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1

Hello, I don’t find any common approach to start heavy work or children’s processes after DynamicSupervisor started. When we restart application or DynamicSupervisor is crash, we need to start DynamicSupervisor children’s processes or do heavy work as the handle_continue function when we use GenServer. In our project, we use start_link for this:

defmodule SomeDynamicSupervisor do

  use DynamicSupervisor
  alias SomeGenServer

  def start_link(_) do
    with link <- DynamicSupervisor.start_link(__MODULE__, %{}, name: __MODULE__) do
      Task.async(fn -> start_child_processors() end)
      link
    end
  end

  def init(_) do
    DynamicSupervisor.init(strategy: :one_for_one, max_restarts: 10)
  end

  def start_child_processors do
    SomeLogic.list_of_ids()
    |> Enum.each(&init_processor/1)
  end

  def init_processor(some_id) do
   
    opts = [name: NameGenerator.processor_registry_name(some_id)]

    DynamicSupervisor.start_child(__MODULE__, %{
      id: "#{SomeGenServer}_#{some_id}",
      start: {SomeGenServer, :start_link, [opts]}
    })
  end
end

What pitfalls does this approach have? Perhaps there is a better way. Can anyone share it with me?

2

Why would you use a DynamicSupervisor is instead of a static/normal one here? It feels like a normal supervisor would suite your need better.

1 Like
3

I need to create processes dynamically. But it’s not matter. My question what the best practice to start a bunch of children processes when we start DynamicSupervisor.

4

I would nest the DynamicSupervisor under another Supervisor with the strategy :rest_for_one and also add a setup Task after the DynamicSupervisor in that supervisor.

Supervisor(strategy: :rest_for_one)
  |----> DynamicSupervisor
  |----> SetupTask / GenServer

If your DynamicSupervisor crash it will be detected by the Supervisor.

  • It will kill the SetupTask / GenServer
  • restart DynamicSupervisor
  • restart your SetupTask / GenServer
1 Like
5

Great, we also considered this option. But we wanted to make it a little easier for understanding and putted the warm-up function to DynamicSupervisor. Also, DynamicSupervisor started by application.ex so supervisor up it if it fails and DynamicSupervisor run warm-up function itself. One best thing that start_link guaranteed that DynamicSupervisor is up.

6

Ordering for supervisor children is guaranteed. If the process to start your task is after the DynamicSupervisor child then it will only run once the DynamicSupervisor is indeed successfully started. You’re not making this simpler, by trying to mush together different responsibilities.

2 Likes
7

Yes, maybe you are right that we need to share responsibility like suggest @kwando:

Supervisor(strategy: :rest_for_one)
  |----> DynamicSupervisor
  |----> SetupTask / GenServer