GenServer call inside macro - macros

Question

I defined a macro like this:
defmodule Test do
defmacro __using__ do
quote do
require Test
import Test
end
end
defmacro my_macro do
quote do
Gernserver.call() # generic server call from other module
end
end
end
I have this code inside a lib which I am building. When testing this lib in a different application I get a compile error on the file which has the use Test.
Error: exited in: GenServer.call ... exit no process (on the line of the my_macro call, more specifically on the genserver call). As if the genserver was not running, and it is not because it is compile time.
Adding a simple Application.ensure_all_started(:lib_name) to the using macro seems to fix the problem. But then again, at compile time the code shouldn't be running, am I right ? Or is here something I am not seeing ? Maybe I can not use genserver calls on a macro ?
Thanks.

Answer 1

You are calling every in your TestScheduler during compilation stage.
One should either put all the schedule initialization code inside a function, that would be called explicitly during run stage, or simply
introduce a new GenServer, add it to supervised list (to make Elixir to run it automatically on app start,) and perform this every initialization in it’s start_link (or any other function that would be called later explicitly):
defmodule Test.Scheduler do
use GenServer
use Cronex.Scheduler
def start_link ... do
every :minute do
IO.puts "every minute job"
end
every :minute do
IO.puts "every minute job 2"
end
end
end
Another way round (if you want to keep the file above as clean as possible,) would be to collect data in every macro, and to spawn all the calls during run stage.
To become more familiar with stages, put the following code into /tmp/test.ex:
defmodule A do
IO.puts "Here “every” macro was called: compilation"
def a do
IO.puts "Is not called during compilation stage"
end
end
IO.puts "=== compilation finished ==="
A.a
And issue elixir /tmp/test.ex:
Here “every” macro was called: compilation
=== compilation finished ===
Is not called during compilation stage