Hi,

I want to handle the following exit example ( String.to_integer(input) is jus an example and can be replaced with raise). This happen when I call My.GenServer.some_method(My.GenServer, "test"). I will be grateful if someone has a suggestion for this.

10:26:42.321 [error] GenServer My.GenServer terminating
** (stop) exited in: Task.await(%Task{owner: #PID<0.124.0>, pid: #PID<0.128.0>, ref: #Reference<0.4181578440.4035444737.94083>}, 5000)
    ** (EXIT) an exception was raised:
        ** (ArgumentError) argument error
            :erlang.binary_to_integer("test")

Here’s the code:

defmodule My.Application do
  use Application

  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    children = [
      worker(My.GenServer, []),
      supervisor(Task.Supervisor, [[name: My.Task.Supervisor, restart: :transient]]),
    ]
    
    opts = [strategy: :one_for_one, name: Test.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

defmodule My.GenServer do
    def start_link do
      GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
    end

    def init(:ok) do
      # Process.flag(:trap_exit, true)
      {:ok, []}
    end

    def some_method(pid, input) do
        GenServer.call(pid, {:some_method, input})
    end

    def handle_call({:some_method, input}, _from, state) do
      # because we don't want to terminate GenServer use Task.async_nolink
      task = Task.Supervisor.async_nolink(My.Task.Supervisor, fn ->
          # raise argument error when passing binary
          String.to_integer(input)
      end)
      {:reply, Task.await(task), state}
    end

    def handle_info({:EXIT, from, reason}, state) do
      IO.inspect "handle_info::exit"
      IO.inspect reason
      {:noreply, state}
    end

    def handle_info({_ref, result}, state) do
      IO.inspect "handle_info::result"
      IO.inspect result
      {:noreply, state}
    end

    def handle_info({:DOWN, _ref, :process, _pid, reason}, state) do
      IO.inspect "handle_info::down"
      IO.inspect reason
      {:noreply, state}
    end

    def handle_info(msg, state) do
      IO.inspect "handle_info"
      IO.inspect msg
      {:noreply, state}
    end
end

I’ve read the docs from here regarding Task.Supervisor.async_link: if you create a task using async_nolink inside an OTP behaviour like GenServer, you should match on the message coming from the task inside your GenServer.handle_info/2 callback.

My problem is that handle_info is not called, I try to debug using observer attaching a trace to My.GenServer and I see that My.GenServer is receiving a :DOWN message:

observer_trace.png856×636 73.3 KB

observer_message.jpg1568×849 87.3 KB

Any solution to this problem ?
Thanks