non working supervisor

defmodule App do
  use GenServer

  def start_link([]) do
    GenServer.start_link(__MODULE__, [])
  end

  def init(state) do
     {:ok, state}
  end

  def get_state(pid) do
     GenServer.call(pid, :get_state)
  end

  def set_state(pid,state) do
     GenServer.call(pid, {:set_state, state})
  end


  def handle_call(:get_state, _from, state) do
     {:reply, state, state}
  end


  def handle_call({:set_state, new_state}, _from, state)do
    {:reply,state,[new_state | state]}
  end
   
end

defmodule App.Supervisor do
  use Supervisor

  def start_link([])do
    Supervisor.start_link(__MODULE__, [])
  end

  def init(_) do
     children = [
        {App, []}
     ]
  Supervisor.init(children, strategy: :one_for_one)
  end
end





App.Supervisor.start_link([])

{:ok, pid} = App.start_link([])

Process.exit(pid, :kill)

pid = Process.whereis(App)

IO.inspect pid

defmodule App do
  use GenServer

  def start_link([]) do
    # give the genserver a name, so you can `whereis` it later
    GenServer.start_link(__MODULE__, [], name: :the_app_process)
  end

  def init(state) do
     {:ok, state}
  end

  def get_state(pid) do
     GenServer.call(pid, :get_state)
  end

  def set_state(pid,state) do
     GenServer.call(pid, {:set_state, state})
  end


  def handle_call(:get_state, _from, state) do
     {:reply, state, state}
  end


  def handle_call({:set_state, new_state}, _from, state)do
    {:reply,state,[new_state | state]}
  end
   
end

defmodule App.Supervisor do
  use Supervisor

  def start_link([])do
    Supervisor.start_link(__MODULE__, [])
  end

  def init(_) do
     children = [
        {App, []}
     ]
    Supervisor.init(children, strategy: :one_for_one)
  end
end





App.Supervisor.start_link([])
app_pid = Process.whereis(:the_app_process)
Process.exit(app_pid, :kill)
Process.whereis(:the_app_process)

# {:ok, pid} = App.start_link([])
# Process.exit(pid, :kill)
# pid = Process.whereis(App)
# IO.inspect pid