Elixir developer `iex` does not load module that uses macro, when it is compiled

Questions / Help
1

Hello friends, I do not think this problem of mine exists in production build ( I did not test it), but in developer mode iex -S mix.

imagine you have this module

defmodule PluginWorker do
  use Worker, concurrency: 1
  
  def perform(event: event, type: :start) do
    ....
  end
end

If I run my iex, and call it inside the function_exported? it returns true.

but when I use it like this:

  @impl true
  # The task completed successfully
  def handle_info({ref, _answer}, %{ref: ref} = state) do
 
    Process.demonitor(ref, [:flush])
    
    # HERE
    function_exported?(PluginWorker, :worker?, 0)
    |> IO.inspect(label: "=-==-=-=>") # false

    Queue.new(%{
      worker: PluginWorker,
      error: %{type: :continuously, max_try: 5, delay: 1000}
    })

    {:noreply, %{state | ref: nil}, {:continue, :start_service_restoring}}
  end

As you see it returns false my question is, how can have this builded in iex developer env and test, and the other problem is, it is a problem in production build? like release

Test mode

In test mode I am forced to call some modules in test_helper.exs file before testing, because without it inside my tests they are no be compiled before

for example:

ExUnit.start()

# Help to compile workers
MishkaInstallerTest.Support.MisWorkerOne.worker?()
WorkerTwo.worker?()
WorkerThree.worker?()
PluginWorker.worker?()

Thank you in advance

2

In dev and test modes the system is running in interactive mode, so the module may not be available before you try to use it. You can use ensure_loaded!/1 before function_exported?/3 to force the BEAM to load it. You wouldn’t have this problem in production because all modules are loaded at start-up in embedded mode.

Code loading on the Erlang VM

1 Like
3

Thank you, so I need to limit it just to use in dev and test (Mix.env()), because the Code.ensure_loaded speed is very low Should I use `Code.ensure_loaded?/1`? - #5 by shahryarjb, when you are using it more than 1 time

4

I think you can use it in the module declaration just above the handle callback, then it’s only run once during compilation

1 Like
5

Yes after your help, I put it like this

defmodule MishkaInstaller.PluginsManagement.Event do
  use GuardedStruct
  use GenServer
  ...
  import MnesiaAssistant, only: [er: 1, erl_fields: 4]

  if Mix.env() in [:dev, :test] do
    Code.ensure_loaded(PluginWorker)
  end

 def ... do
    ....
 end
1 Like
6

Great!

Just 2 things to keep in mind.

You don’t need to test for the environment.

If the module is already loaded, this works as no-op. If the module was not yet loaded, it tries to load it.

Maybe use the ! version so the compiler fails in case the module isn’t found, otherwise you’ll only find out at runtime like you saw in your failing tests.

2 Likes