example gen_server

gs.erl

-module(gs).
-behaviour(gen_server).

-export([start/0, stop/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
         terminate/2, code_change/3]).

-record(state, {count}).

start() ->
    gen_server:start({local, ?MODULE}, ?MODULE, [], [{debug,[trace]}]).

stop() ->
    gen_server:cast(?MODULE, stop).

init([]) ->
    gen_server:cast(self(), step1),
    {ok, #state{count=0}}.

handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

handle_cast(step1, #state{count=3}=State) ->
    {stop,normal,State};
handle_cast(step1, State) ->
    gen_server:cast(self(), step2),
    {noreply, State};
handle_cast(step2, State) ->
    gen_server:cast(self(), step3),
    {noreply, State};
handle_cast(step3, State) ->
    gen_server:cast(self(), step4),
    {noreply, State};
handle_cast(step4, State) ->
    gen_server:cast(self(), step5),
    {noreply, State};
handle_cast(step5, #state{count=Count}=State) ->
    gen_server:cast(self(), step1),
    {noreply, State#state{count=Count+1}};
handle_cast(stop, State) ->
    {stop,normal,State};
handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info(_Info, State) ->
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.