gen_server_consumer.erl

process(Data) ->
  gen_server:cast(?SERVER, {process, Data});

...

handle_cast({process, Data}, {}) ->
  do_some_funky_stuff(Data),
  reader:pop(self);
  {ok, {}}

gen_server_queu.erl

pop(Reader) ->
  gen_server:cast(?SERVER, {pop, Reader});

push(Data) ->
  gen_server:cast(?SERVER, {push, Data});

...

handle_cast({pop, Reader}, {[], Readers}) ->
  {ok, {[], [Reader | Readers]}};

handle_cast({pop, Reader}, {[Data | R], []}) ->
  consumer:process(Reader, Data),
  {ok, {R, []}};


handle_cast({pop, Reader}, {[Data | R], [First | Rdrs]}) ->
  consumer:process(First, Data),
  {ok, {R, [Reader | Rdrs]}};

handle_cast({push, Data}, {Dates, []}) ->
  {ok, {[Data| Dates], []}};

handle_cast({push, Data}, {[], [First | Rdrs]}) ->
  consumer:process(First, Data),
  {ok, {[], Rdrs}};