Erlang Concurrency

%% Basic process spawning
simple_spawn() ->
    Pid = spawn(fun() ->
        io:format("Hello from process ~p~n", [self()])
    end),
    Pid.

%% Spawn with arguments
spawn_with_args(Message) ->
    spawn(fun() ->
        io:format("Message: ~p~n", [Message])
    end).

%% Spawn and register
spawn_registered() ->
    Pid = spawn(fun() -> loop() end),
    register(my_process, Pid),
    Pid.

loop() ->
    receive
        stop -> ok;
        Msg ->
            io:format("Received: ~p~n", [Msg]),
            loop()
    end.

%% Spawn link (linked processes)
spawn_linked() ->
    spawn_link(fun() ->
        timer:sleep(1000),
        io:format("Linked process done~n")
    end).

%% Spawn monitor
spawn_monitored() ->
    {Pid, Ref} = spawn_monitor(fun() ->
        timer:sleep(500),
        exit(normal)
    end),
    {Pid, Ref}.

%% Process pools
create_pool(N) ->
    [spawn(fun() -> worker_loop() end) || _ <- lists:seq(1, N)].

worker_loop() ->
    receive
        {work, Data, From} ->
            Result = process_data(Data),
            From ! {result, Result},
            worker_loop();
        stop ->
            ok
    end.

process_data(Data) -> Data * 2.

%% Parallel map
pmap(F, List) ->
    Parent = self(),
    Pids = [spawn(fun() ->
        Parent ! {self(), F(X)}
    end) || X <- List],
    [receive {Pid, Result} -> Result end || Pid <- Pids].


%% Fork-join pattern
fork_join(Tasks) ->
    Self = self(),
    Pids = [spawn(fun() ->
        Result = Task(),
        Self ! {self(), Result}
    end) || Task <- Tasks],
    [receive {Pid, Result} -> Result end || Pid <- Pids].

%% Send and receive
send_message() ->
    Pid = spawn(fun() ->
        receive
            {From, Msg} ->
                io:format("Received: ~p~n", [Msg]),
                From ! {reply, "Acknowledged"}
        end
    end),
    Pid ! {self(), "Hello"},
    receive
        {reply, Response} ->
            io:format("Response: ~p~n", [Response])
    after 5000 ->
        io:format("Timeout~n")
    end.

%% Request-response pattern
request(Pid, Request) ->
    Ref = make_ref(),
    Pid ! {self(), Ref, Request},
    receive
        {Ref, Response} -> {ok, Response}
    after 5000 ->
        {error, timeout}
    end.

server_loop() ->
    receive
        {From, Ref, {add, A, B}} ->
            From ! {Ref, A + B},
            server_loop();
        {From, Ref, {multiply, A, B}} ->
            From ! {Ref, A * B},
            server_loop();
        stop -> ok
    end.

%% Publish-subscribe
start_pubsub() ->
    spawn(fun() -> pubsub_loop([]) end).

pubsub_loop(Subscribers) ->
    receive
        {subscribe, Pid} ->
            pubsub_loop([Pid | Subscribers]);
        {unsubscribe, Pid} ->
            pubsub_loop(lists:delete(Pid, Subscribers));
        {publish, Message} ->
            [Pid ! {message, Message} || Pid <- Subscribers],
            pubsub_loop(Subscribers)
    end.

%% Pipeline pattern
pipeline(Data, Functions) ->
    lists:foldl(fun(F, Acc) -> F(Acc) end, Data, Functions).

concurrent_pipeline(Data, Stages) ->
    Self = self(),
    lists:foldl(fun(Stage, AccData) ->
        Pid = spawn(fun() ->
            Result = Stage(AccData),
            Self ! {result, Result}
        end),
        receive {result, R} -> R end
    end, Data, Stages).

%% Process linking
link_example() ->
    process_flag(trap_exit, true),
    Pid = spawn_link(fun() ->
        timer:sleep(1000),
        exit(normal)
    end),
    receive
        {'EXIT', Pid, Reason} ->
            io:format("Process exited: ~p~n", [Reason])
    end.

%% Monitoring
monitor_example() ->
    Pid = spawn(fun() ->
        timer:sleep(500),
        exit(normal)
    end),
    Ref = monitor(process, Pid),
    receive
        {'DOWN', Ref, process, Pid, Reason} ->
            io:format("Process down: ~p~n", [Reason])
    end.

%% Supervisor pattern
supervisor() ->
    process_flag(trap_exit, true),
    Worker = spawn_link(fun() -> worker() end),
    supervisor_loop(Worker).

supervisor_loop(Worker) ->
    receive
        {'EXIT', Worker, _Reason} ->
            NewWorker = spawn_link(fun() -> worker() end),
            supervisor_loop(NewWorker)
    end.

worker() ->
    receive
        crash -> exit(crashed);
        work -> worker()
    end.