Critical Patterns

OTP GenServer (REQUIRED)

-module(counter). -behaviour(gen_server). -export([start_link/0, increment/0, get/0]). -export([init/1, handle_call/3, handle_cast/2]).

start_link() -> gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

init([]) -> {ok, 0}.

handle_call(get, _From, State) -> {reply, State, State}.

handle_cast(increment, State) -> {noreply, State + 1}.

Supervisor (REQUIRED)

-module(my_sup). -behaviour(supervisor). -export([start_link/0, init/1]).

start_link() -> supervisor:start_link({local, ?MODULE}, ?MODULE, []).

init([]) -> SupFlags = #{strategy => one_for_one, intensity => 5, period => 10}, Children = [ #{id => worker, start => {my_worker, start_link, []}} ], {ok, {SupFlags, Children}}.

Decision Tree

Need request/response? → Use gen_server call Need fire-and-forget? → Use gen_server cast Need supervision? → Use supervisor behavior Need state machine? → Use gen_statem Need event handling? → Use gen_event

Commands

erl # Start REPL erlc module.erl # Compile rebar3 compile # Build project rebar3 shell # Interactive shell

Resources

• Concurrent Programming: concurrent-programming.md

• Fault Tolerance: fault-tolerance.md

• OTP Patterns: otp-patterns.md