Question

我已经开始学习Erlang了，我已经开始使用邮箱和服务器，我的代码遇到了一个我不理解的错误

start()->
Counter = spawn(fun counter/0),
client(Counter).

counter(N) ->
receive
    {get_state, P} -> P!N;
    {inc_state} -> N+1
end.

client(P) ->
N!get_state,
    timer:sleep(100 + rand:uniform(900)),
N!inc_state,
    timer:sleep(100 + rand:uniform(900)),
done.

我在N上得到未绑定的错误而在P.上未使用

Answer 1

-module(counter).

-compile([export_all]).

    start()->
        Counter = spawn(fun counter/0),
        client(Counter).

    % you have started your counter without parameter, (this is the meaning of
    % counter/0) this intermediate function call the counter with the init value 0.
    counter() -> counter(0).

counter(10) ->
    io:format("counter has reach 10, it stops~n");
counter(N) ->
    NewCount = receive
        {get_state, P} ->
            % send the answer
            P ! N,
            % and keep the state unchanged
            N;
        {inc_state} ->
            N+1
    end,
    % never forget to do a recursive loop if you want that your process keep alive!
    counter(NewCount).

client(stop) ->
    io:format("client has not receive any answer, it stops~n");
client(P) ->
    % the pid of your server is P, and you have to respect your message definition,
    % what is expected by the server
    % in your code you are using N instead, which is undefined (unbound),
    % and you don't use P: this is the reason of the error and warning messages.
    P ! {get_state,self()},
    timer:sleep(100 + rand:uniform(900)),
    % add this to show that the state is incrementing
    Continue = receive
        State ->
            io:format("state is ~p~n",[State]),
            P
        after 1000 ->
            stop
    end,
    P ! {inc_state},
    timer:sleep(100 + rand:uniform(900)),
    % recursive loop otherwise it will stop at the first step, leaving a counter process alive.
    % my proposal to stop these processes.
    client(Continue).

变量N是未绑定的，P未使用，如何解决？

1 个答案: