A very busy server that blocks its clients

busy.erl

-module busy.

-export [loop/0].
-export [test/0].

test() ->
  start_server(),
  {error, server_down} = call(server, die), % Your code will catch this
  start_server(),
  pong = call(server, ping_and_sleep),
  pong = call(server, ping), % Your code will block here forever
  passed.

start_server() ->
  Server = spawn(busy, loop, []),
  register(server, Server).

call(RegName, Request) ->
  Ref = monitor(process, whereis(RegName)),
  RegName ! {request, self(), Ref, Request},
  receive
    {reply, Ref, Reply} ->
      demonitor(Ref, [flush]),
      Reply;
    {'DOWN', Ref, process, Pid, Info} ->
      io:format("Pid ~p Info ~p~n", [Pid, Info]),
      {error, server_down}
  end.

loop() ->
  receive
    {request, From, Ref, ping} ->
        From ! {reply, Ref, pong},
        loop();
    {request, _, _, die} ->
        io:format("Server ~p dying~n", [self()]),
        dying;
    {request, From, Ref, ping_and_sleep} ->
        From ! {reply, Ref, pong},
        receive
            [something, that, will, never, come] ->
                loop()
        end
end.