gen_server:call - how to send message - erlang

Question

Now Im playing with the gen_server
I have two modules - one is Gen Server mod, second - logic module
and would like to send the message to the PID through the gen_server:call
here is the snip of code:
lookup_by_date(FromTime, ToTime) ->
gen_server:call({global, ?MODULE}, {lookup_by_date,FromTime,ToTime}).
here is the handle_call func:
handle_call({lookup_by_date, FromTime, ToTime}, _From, _State) ->
FromSec = calendar:datetime_to_gregorian_seconds(FromTime),
ToSec = calendar:datetime_to_gregorian_seconds(ToTime),
Pid = spawn(fun()-> logic:handler() end),
{reply, Pid !{lookup_by_date, FromSec, ToSec}, _State};
aand the logic mod code:
lookup_by_date(FromTime, ToTime) -> lookup_by_date(FromTime, ToTime, ets:first(auth), []).
lookup_by_date(_FromTime, _ToTime, '$end_of_table', Acc) -> {reply, Acc, ok};
lookup_by_date(FromTime, ToTime, Key, Acc) ->
case ets:lookup(auth, Key) of
[{Login, Pass, TTL, Unix, Unix2}] ->
F = calendar:datetime_to_gregorian_seconds(Unix2),
T = calendar:datetime_to_gregorian_seconds(Unix2),
if
F >= FromTime, T =< ToTime -> NewAcc = [{Login, Pass, TTL, Unix, Unix2}|Acc],
N = ets:next(auth, Key),
lookup_by_date(FromTime, ToTime, N, NewAcc);
true -> N = ets:next(auth, Key),
lookup_by_date(FromTime, ToTime, N, Acc)
end
end.
handler() ->
receive
{lookup_by_date, FromTime, ToTime}->
lookup_by_date(FromTime, ToTime),
handler();
Other->
io:format("Error message for ~p~n" ,[Other]),
handler()
end.
but i am getting the error (actually not an error)
2> c(cache_server).
{ok,cache_server}
3> c(logic).
{ok,logic}
4> cache_server:start([{ttl, 15000}]).
{ok,<0.73.0>}
5> cache_server:insert(test, root, 15000).
{auth,test,root,15000,1484309726435,
{{2017,1,13},{14,15,11}}}
6> cache_server:lookup_by_date({{2017,1,13},{14,15,11}},{{2017,1,13},{14,15,11}}).
{lookup_by_date,63651536111,63651536111}
I am receiving data from - {reply, Pid !{lookup_by_date, FromSec, ToSec}, _State};
but dont receive data from the "logic:lookup_by_date" function
Is there anyway you show me the right direction because Im stuck a little bit.
Thx...

Answer 1

In your code, the reply to the gen_server call is:
Pid !{lookup_by_date, FromSec, ToSec}
In Erlang messages are asynchronous, they are just sent to the process, so this code doesn't wait for a response, and it simply returns, immediatly, the message you are sending. It is why you get the reply {lookup_by_date, FromSec, ToSec}.
In your case you don't have to spawn a process, but simply call the lookup_by_date function:
handle_call({lookup_by_date, FromTime, ToTime}, _From, _State) ->
FromSec = calendar:datetime_to_gregorian_seconds(FromTime),
ToSec = calendar:datetime_to_gregorian_seconds(ToTime),
{reply, logic:lookup_by_date(FromSec, ToSec), _State};
Note: Your gen_server doesn't use the result, its state is not modified by the request, so you could directly call the function lookup_by_date and include the time conversion in it.