send message to gen_server before init

Question

I am new to erlang, I having following code:

-module (test_srv).
-behaviour (gen_server).
-export ([start_link/0, init/1, handle_info/2]).

start_link() ->
  gen_server:start_link(?MODULE, [], []).

init([]) ->
  self() ! asdasd,
  {ok, new_state}.

handle_info(Msg, State) ->
  io:format("server got ~p , now state is ~p~n", [Msg, State]),
  {noreply, State}.

I test in erl shell:

1> {_, P} = test_srv:start_link().
server got asdasd , now state is new_state

The problem is, When send a message to server when the server is not initialised and not readly, how dose gen_server handle the message? I have following guesses:

gen_server handle the message immediately, and send the message to handle_info callback, but will lose initialised state in init callback
gen_server store the message if not server initialised, and send message after server initialised.

I wanna to know how erlang or gen_server handle this problem? what is the principle of handle message?

Dogbert Dogbert · Accepted Answer · 2016-10-14T04:47:35

I'm guessing by server is not initialised you mean the rest of the init function being executed. In that case your second guess is correct. It's guaranteed that the handle_info will be executed after init has returned. Since the gen_server is a single process, and you're already executing init, the messages sent to itself from init will only be processed by gen_server after init has finished executing.

send message to gen_server before init

1 Answers