Optimized way of getting values from an erlang process loop - erlang

Question

Hi I'm a newbie in Erlang and I just started learning about processes. Here I have a typical process loop:
loop(X,Y,Z) ->
receive
{do} ->
NewX = X+1,
NewY = Y+1,
NewZ = Z+1,
Product = NewX * NewY * NewZ,
% do something
loop(NewX,NewY,NewZ)
end.
How do I get the latest value of Product from a function let's say get_product()? I know that message passing will be the logical option but is there a more optimal way of extracting the value?

Answer 1

Here are methods to communicate between Erlang processes I am aware of, and my (possibly wrong) assessment of theirs relative performance.
Message passing. This method will suit most of your needs. I don't know how it is actually implemented, but from my point of view it should be as fast as putting a pointer into a queue and retrieving it back.
Exterior methods, e.g. sockets, files, pipes. These methods might be faster for communicating between different nodes, depending on a problem you solve, your solution and environment your program will be executed in. Inter-node communication in Erlang is done via TCP connections, so if you want to use self written code to communicate via TCP sockets, you should try really hard to outperform Erlang's implementation.
ETS, Dets. These methods won't be faster than message passing (ETS) or file (Dets) assuming best possible implementation.
NIF. You can write one method to save value in your NIF library and one to retrieve it. This one has a potential to outperform message passing since you can just save a value into a variable and return it back when needed and it has no overhead on pattern matching in receive.
Process dictionary. You can get another process dictionary using erlang:process_info(Pid, dictionary) call, in the Pid process you can put value in that dictionary using put(Key, Value) call.
Also, if you want to speed up your Erlang application take a look at HiPE, it might help.
Before switching from message passing to anything from this list to gain in speed you should measure it first!

Answer 2

I assumed this is what you want:
-module(lab).
-compile(export_all).
start() ->
InitialState = {1,1,1},
Pid = spawn(?MODULE, loop, [InitialState]),
register(server, Pid).
loop(State) ->
{X, Y, Z} = State,
receive
tick ->
NewX = X+1,
NewY = Y+1,
NewZ = Z+1,
NewState = {NewX, NewY, NewZ},
loop(NewState);
{get_product, From} ->
Product = X * Y * Z,
From ! Product,
loop(State);
_ ->
io:format("Unknown message received.~n"),
loop(State)
end.
get_product() ->
server ! {get_product, self()},
receive
Product ->
Product
end.
tick() ->
server ! tick.
From within the Erlang shell:
1> c(lab).
{ok,lab}
2> lab:start().
true
3> lab:get_product().
1
4> lab:tick().
tick
5> lab:get_product().
8
6> lab:tick().
tick
7> lab:tick().
tick
8> lab:get_product().
64