Erlang/OTP gen_server simplified API, basics

gistfile1.md

Client side API

Start a gen_server programmatically

gen_server:start(ModuleName, Arguments, Options) -> {ok, Pid} | {error, Reason}

gen_server:start(ServerName, ModuleName, Arguments, Options) -> {ok, Pid} | {error, Reason}

(Also gen_server:star_link/3 and gen_server:start_link/4 variants)

Synchronous calls

gen_server:call(PidOrName, Message) -> ReplyMessage

gen_server:call(PidOrName, Message, Timeout)

Asynchronous call (cast)

gen_server:cast(PidOrName, Message)

Server API, most important callbacks

Callback module declaration

-module(your_module_name).
-behaviour(gen_server).

Essential callbacks

init(Arguments) -> {ok, InitialState} | {stop, Reason}

handle_call(Message, From, CurrentState) -> {reply, ReplyMessage, NewState} | {noreply, NewState} | {stop, Reason, NewState}

handle_cast(Message, CurrentState) -> {noreply, NewState} | {stop, NewState}

handle_info(Message, CurrentState) -> {noreply, NewState} | {stop, NewState}

terminate(Reason, State) -> ReturnValueIgnored