How do i call handle_call outside module?

Questions / Help
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1

I have defined a module GS where genserver will be used and I need to create tables. I have the whole logic of the program In another module named base. How do I inherit handle_call in my genserver GS module ?

GS MODULE:

defmodule GS do
  use GenServer
  @name gen
  # client
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, [], opts ++ [name: gen])
  end

  def creating_tables(tables_list) do
    GenServer.call(@name, {:creating_tables, tables_list})
  end

  # server
  def init(initial_state) do
    {:ok, initial_state}
  end
end

BASE MODULE

defmodule Base do
  def handle_call({:creating_tables}, _from, state_tables_list) do
    tables = Enum.map(state_tables_list, fn table -> create(table) end)
    {:reply, tables, state_tables_list}
  end

  defp create(table) do
    try do
      :ets.new(table, [:named_table, :bag])
    rescue
      ArgumentError -> table
    end
  end
end
2

Why do you want to extract this function from the GS module? Do you want to create an extended genserver?

I think handle_call has to be in the genserver module as it is a callback implementation.
If you want, you can extract the logic of the table creation in another module and use it in your genserver.

3

Thanks for such a prompt response. Actually, I will have other features in my Base module which i want to affiliate with other genserver. Keeping them under ‘GS’ will make it crowded.

4

I will be happy to help. I need more infos.
Why it is a Base? What is the role of this module?

5

So Base is like a Base table in database where tables can be created or deleted and also can add or delete data from it. GS will be a genserver module where i can create multiple tables concurrently and later in my program add data to tables concurrently.

6

In this case, keep the handle_call function in GS. The Base module is a TableCreator (surely, you can find a better name)

defmodule TableCreator do
   def create_tables(tables) when is_list(tables) do
      tables |> Enum.map(fn table -> create(table) end)
   end

  defp create(table) do
    try do
      :ets.new(table, [:named_table, :bag])
    rescue
      ArgumentError -> table
    end
  end
end

and in the genserver module the function handle_call would be

def handle_call({:creating_tables}, _from, state_tables_list) do
    tables = TableCreator.create_tables(state_tables_list)
    {:reply, tables, state_tables_list}
  end

i hope it helps :wink:

3 Likes
7

So, Basically i must have to use handle call inside my GenServer.

8

I agree with @Laetitia and will add that handle_call and the tuple it returns is your contract with GenServer. That logic belongs in the GenServer callback module. But you can certainly call out to shared logic in another module in the body of the function.

I’d also caution you about bottlenecking your system. You seem to want to make it easy to create multiple ets tables. Those are owned by a process for lifecycle management purposes and you’re not making them public (nor are you accepting a parameter to do so) so all access will have to go through a single GenServer, which only handles a single message at a time.

1 Like
9

Yes, I agree, and thanks a lot for such valuable feedback. Actually, I will make each :ets table a separate table. So, all the entries to a single table are handled by a separate process. I was wrong initially when I stated that each would have a separate process. Thanks for correcting me.

10

You must define handle_call/3 in the module you give to GenServer.start_link/3.

Your code:

 GenServer.start_link(__MODULE__, [], opts ++ [name: gen])

Here you give __MODULE__, so you give GS.

1 Like