%%% $Id: runavg.erl,v 1.1 2013/04/17 01:02:33 leavens Exp leavens $ %%%------------------------------------------------------------------- %%% @author Gary T. Leavens %%% @doc A simple example of the use of Erlang's gen_server module. %%% This tracks a running average of 3 floats. Floats are sent to %%% the server by using the function note/1. %%% The current average can be obtained by calling average/0. %%% @end %%%------------------------------------------------------------------- -module(runavg). -behaviour(gen_server). %% API -export([start_link/0, note/1, average/0]). %% gen_server callbacks -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]). -define(SERVER, ?MODULE). % the state is a tuple of 3 floats, with the leftmost being the oldest % starting out as {0.0, 0.0, 0.0} %%%=================================================================== %%% API %%%=================================================================== note(Measurement) -> gen_server:call(?MODULE, {note, Measurement}). average() -> gen_server:call(?MODULE, average). %%-------------------------------------------------------------------- %% @doc %% Starts the server %% %% @spec start_link() -> {ok, Pid} | ignore | {error, Error} %% @end %%-------------------------------------------------------------------- start_link() -> gen_server:start_link({local, ?SERVER}, ?MODULE, [], []). %%%=================================================================== %%% gen_server callbacks %%%=================================================================== %%-------------------------------------------------------------------- %% @private %% @doc %% Initializes the server %% %% @spec init(Args) -> {ok, State} | %% {ok, State, Timeout} | %% ignore | %% {stop, Reason} %% @end %%-------------------------------------------------------------------- init([]) -> {ok, {0.0, 0.0, 0.0}}. %%-------------------------------------------------------------------- %% @private %% @doc %% Handling call messages %% %% @spec handle_call(Request, From, State) -> %% {reply, Reply, State} | %% {reply, Reply, State, Timeout} | %% {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, Reply, State} | %% {stop, Reason, State} %% @end %%-------------------------------------------------------------------- handle_call({note,Measurement}, _From, {_M1,M2,M3}) -> Reply = ok, {reply, Reply, {M2,M3,Measurement}}; handle_call(average, _From, {M1,M2,M3}) -> Avg = (M1+M2+M3)/3.0, {reply, Avg, {M1,M2,M3}}. %%-------------------------------------------------------------------- %% @private %% @doc %% Handling cast messages %% %% @spec handle_cast(Msg, State) -> {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, State} %% @end %%-------------------------------------------------------------------- handle_cast({note,Measurement}, {_M1,M2,M3}) -> {noreply, {M2,M3,Measurement}}. %%-------------------------------------------------------------------- %% @private %% @doc %% Handling all non call/cast messages %% %% @spec handle_info(Info, State) -> {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, State} %% @end %%-------------------------------------------------------------------- handle_info(_Info, State) -> {noreply, State}. %%-------------------------------------------------------------------- %% @private %% @doc %% This function is called by a gen_server when it is about to %% terminate. It should be the opposite of Module:init/1 and do any %% necessary cleaning up. When it returns, the gen_server terminates %% with Reason. The return value is ignored. %% %% @spec terminate(Reason, State) -> void() %% @end %%-------------------------------------------------------------------- terminate(_Reason, _State) -> ok. %%-------------------------------------------------------------------- %% @private %% @doc %% Convert process state when code is changed %% %% @spec code_change(OldVsn, State, Extra) -> {ok, NewState} %% @end %%-------------------------------------------------------------------- code_change(_OldVsn, State, _Extra) -> {ok, State}.