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Erlang OTP: Distributed & Fault-Tolerant Systems Programming · 강의

이벤트 처리를 위한 GenEvent

GenEvent를 사용하여 결합도를 낮춘 이벤트 처리 시스템을 만들고 게시자와 구독자가 비동기적으로 상호 작용하도록 하는 방법을 학습합니다.

이벤트 처리를 위한 GenEvent은(는) CoddyKit의 무료 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 강의입니다. 이것은 4개 중 2번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. Erlang OTP: Distributed & Fault-Tolerant Systems Programming 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Why Event Handling?

Imagine you have many parts of your application that need to react to something happening, like a user logging in.

If each part directly calls every other part, your code becomes tightly coupled and hard to change. This is where event handling comes in!

Introducing GenEvent

Erlang's OTP (Open Telecom Platform) provides a powerful behavior called gen_event for building decoupled event handling systems.

  • It implements the publisher-subscriber pattern.
  • Publishers send events without knowing who will receive them.
  • Subscribers (called handlers) register to receive specific events.
  • This promotes loose coupling and makes systems more flexible.

The Event Manager

At the heart of gen_event is an event manager. This is a special Erlang process that acts as a central hub:

  • It receives events from publishers.
  • It dispatches these events to all registered handlers.

You start an event manager just like other OTP behaviors:

-module(event_manager_starter).
-export([start/0]).

start() ->
    % Start a local event manager named 'my_app_events'
    {ok, Pid} = gen_event:start_link({local, my_app_events}),
    io:format("Event manager started with PID: ~p~n", [Pid]),
    ok.

Event Handlers: The Listeners

An event handler is an Erlang module that implements the gen_event behavior. It defines callback functions that the event manager will call when an event occurs.

Think of handlers as specialized listeners, each interested in certain types of events or performing a specific action when an event is received.

Creating a Simple Handler

Here's the basic structure for an event handler module. The key callback is handle_event/2, where you process the incoming event.

-module(my_event_handler).
-behaviour(gen_event).

-export([init/1, handle_event/2, terminate/2]).

init(Args) ->
    io:format("Handler initialized with args: ~p~n", [Args]),
    {ok, []}. % Returns initial state

handle_event(Event, State) ->
    io:format("Handler received event: ~p~n", [Event]),
    % Here you'd process the event
    {ok, State}. % Return new state

terminate(_Args, _State) ->
    io:format("Handler terminating.~n", []),
    ok.

Adding Handlers to the Manager

After starting your event manager and defining your handler, you need to tell the manager about your handler. This is done using gen_event:add_handler/3.

You can add multiple handlers to the same manager, and each will receive the events.

-module(handler_adder).
-export([add_to_manager/1]).

add_to_manager(ManagerName) ->
    % The handler module name (my_event_handler)
    % and any initial arguments for its init/1 function ([] in this case)
    gen_event:add_handler(ManagerName, my_event_handler, []),
    io:format("Handler 'my_event_handler' added to '~p'.~n", [ManagerName]),
    ok.

Notifying the Manager (Publishing Events)

Once handlers are registered, any part of your application can send an event to the manager using gen_event:notify/2. The manager will then forward this event to all active handlers.

The publisher doesn't know (or care) how many handlers there are, or what they do. This is the power of decoupling!

-module(event_publisher).
-export([send_alert/2]).

send_alert(ManagerName, Message) ->
    Event = {alert, Message, os:timestamp()},
    io:format("Publisher sending event: ~p to manager '~p'.~n", [Event, ManagerName]),
    gen_event:notify(ManagerName, Event).

Full GenEvent Demo

Let's put it all together! This runnable example starts a manager, adds a simple handler, and then sends a few events. Watch the handler react!

-module(gen_event_demo).
-export([start/0]).

% --- Inline Handler Module for Demo ---
% In a real app, this would be a separate .erl file.
my_demo_handler() ->
    % Compile and load a temporary handler module
    code:delete(demo_handler_impl),
    code:purge(demo_handler_impl),
    {ok, _} = compile:forms([
        '-module(demo_handler_impl).',
        '-behaviour(gen_event).',
        '-export([init/1, handle_event/2, terminate/2]).',
        'init(Args) -> {ok, Args}.',
        'handle_event(Event, State) ->',
        '    io:format("*** Handler received: ~p~n", [Event]),',
        '    {ok, State}.',
        'terminate(_Args, _State) -> ok.'
    ], []),
    demo_handler_impl.

% --- Main Application Logic ---
start() ->
    ManagerName = my_system_events,
    HandlerModule = my_demo_handler(),

    io:format("--- Starting GenEvent Demo ---~n"),

    % 1. Start the event manager
    {ok, _ManagerPid} = gen_event:start_link({local, ManagerName}),
    io:format("Manager '~p' started.~n", [ManagerName]),

    % 2. Add the handler to the manager
    gen_event:add_handler(ManagerName, HandlerModule, []), 
    io:format("Handler '~p' added.~n", [HandlerModule]),

    % 3. Publish some events
    io:format("Sending first event...~n"),
    gen_event:notify(ManagerName, {user_logged_in, "Alice"}),
    timer:sleep(100), % Give time for event processing

    io:format("Sending second event...~n"),
    gen_event:notify(ManagerName, {sensor_reading, 25.5}),
    timer:sleep(100),

    io:format("Sending third event...~n"),
    gen_event:notify(ManagerName, {error_alert, "Disk_full"}),
    timer:sleep(100),

    % 4. Stop the manager (optional, for clean exit)
    gen_event:stop(ManagerName),
    io:format("--- GenEvent Demo Finished ---~n"),
    ok.

Advanced GenEvent Usage

gen_event is quite flexible:

  • Handler State: Handlers can maintain their own internal state, updated with each event.
  • Multiple Handlers: A single event manager can have many handlers, each processing events independently.
  • Removing Handlers: Handlers can be dynamically removed using gen_event:delete_handler/3.
  • Synchronous Calls: While primarily asynchronous, gen_event:call/2 allows synchronous calls to handlers (though less common for pure eventing).

GenEvent Quick Check

You've learned about GenEvent's core components and how they interact. Let's test your understanding!

Recap: GenEvent Essentials

Great job! You've learned how gen_event helps build flexible, decoupled systems:

  • Event Manager: The central hub that dispatches events.
  • Event Handlers: Modules that subscribe to and process events.
  • Publishers: Send events to the manager using gen_event:notify/2.
  • Decoupling: Key benefit, allowing parts of your system to evolve independently.

Next, you'll explore even more advanced OTP behaviors!

자주 묻는 질문

“이벤트 처리를 위한 GenEvent” 강의는 무료인가요?

네 — “이벤트 처리를 위한 GenEvent” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 강의 전체를 잠금 해제할 수 있습니다. Erlang OTP: Distributed & Fault-Tolerant Systems Programming 강의에는 총 4개의 강의가 포함되어 있습니다.

“이벤트 처리를 위한 GenEvent”에서 뭘 배우나요?

GenEvent를 사용하여 결합도를 낮춘 이벤트 처리 시스템을 만들고 게시자와 구독자가 비동기적으로 상호 작용하도록 하는 방법을 학습합니다. 브라우저에서 직접 실행하는 실습 코드로 Erlang OTP: Distributed & Fault-Tolerant Systems Programming을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.

Erlang OTP: Distributed & Fault-Tolerant Systems Programming을(를) 시작하는 데 경험이 필요한가요?

사전 경험은 필요하지 않습니다. CoddyKit의 Erlang OTP: Distributed & Fault-Tolerant Systems Programming은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 2번째 강의입니다.

“이벤트 처리를 위한 GenEvent” 강의는 얼마나 걸리나요?

대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.

이 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 강의에서 코드를 작성하고 실행할 수 있나요?

네. 모든 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.

이 강의의 모든 강의

  1. 상태 관리를 위한 GenStatem
  2. 이벤트 처리를 위한 GenEvent
  3. 사용자 지정 OTP 동작
  4. 핫 코드 교체와 실시간 업그레이드
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