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Concurrency Patterns in Erlang

The Request-Response Pattern

Building a Simple Server

Code: Echo Server Example

-module(echo_server).
-export([start/0, loop/0]).

start() ->
    spawn(echo_server, loop, []).

loop() ->
    receive
        {FromPid, Message} ->
            FromPid ! {self(), echoed, Message},
            loop();
        _ ->
            io:format("Server received unknown message.~n"),
            loop()
    end.

Code: Echo Client Interaction

-module(echo_client).
-export([run/0]).

run() ->
    ServerPid = echo_server:start(),
    io:format("Server started with PID: ~p~n", [ServerPid]),

    Request = "Hello Erlang!",
    ServerPid ! {self(), Request},
    io:format("Client sent: ~p to server ~p~n", [Request, ServerPid]),

    receive
        {_ServerPid, echoed, Response} ->
            io:format("Client received reply: ~p~n", [Response]);
        _ ->
            io:format("Client received unexpected message.~n")
    after 5000 ->
        io:format("Client timed out waiting for reply.~n")
    end.

Running the Echo System

The Asynchronous Pattern

Code: Asynchronous Logger Process

-module(async_logger).
-export([start/0, loop/0]).

start() ->
    spawn(async_logger, loop, []).

loop() ->
    receive
        {log, Message} ->
            io:format("LOG: ~p~n", [Message]),
            loop();
        _ ->
            io:format("Logger received unknown message.~n"),
            loop()
    end.

Code: Asynchronous Logger Client

-module(logger_client).
-export([run/0]).

run() ->
    LoggerPid = async_logger:start(),
    io:format("Logger started with PID: ~p~n", [LoggerPid]),

    LoggerPid ! {log, "User X logged in."},
    io:format("Client sent first log. Continuing...~n"),

    timer:sleep(10), % Give logger a moment to process
    LoggerPid ! {log, "User Y viewed profile."},
    io:format("Client sent second log. Task complete.~n").

Concurrency Pattern Check

Recap: Basic Concurrency Patterns