Question

所以我试图在两个客户端和erlang中的服务器之间建立一个聊天系统。我在进入网络时注册每个进程。但是当客户端请求与另一个客户端聊天时，它会进入findUser（）函数，并在目标用户名存在时在注册列表中查找。但由于某种原因，每个客户端用户名都没有被添加到它看起来的相同注册列表中。如何让所有新注册的进程进入同一列表？

服务器端：

-module(hw5server).
-export([start/0, checkUser/2, append/2, findUser/2]).

start() -> spawn(fun loop/0).

findUser(RequestorPid, Receiver) ->
    Reqmessage = io:format("~p would like to chat with you. Press 1 to accept or 2 to decline: ", [RequestorPid]),
    Pid2 = whereis(erlang:list_to_atom(Receiver)),
    Pid2 ! {Pid2, Reqmessage}.  ////////////MY ERROR!!!!

checkUser(Client,Username) ->
    case {lists:member(Username, [userList])} of
            {true} -> Message1 = io:format("Username taken.~n"),
                      Client ! {Message1};
            {false} -> append([userList], Username),
                       Message = io:format("You have been connected!~n"),
                       register(erlang:list_to_atom(Username), Client), //Registers the Client.
                       Client ! {Message}
    end.

append([List|T],User) -> [List|append(T,User)];
append([],User) -> User.

loop() ->
    receive
    {Client, Message} ->
            io:format("Server: received a message!~p~n",[Message]),
            Client ! {Message},
            loop()
    end.

客户端：

-module(hw5client).
-export([start/1,goOnline/2, loop/1, requestChatWith/2]).

start(Server) ->
    %Server = hw5server:start().
    spawn(hw5client, loop, [Server]),
    loop(Server).

goOnline(Client_Node,Username) ->
    hw5server:checkUser(Client_Node, Username),
    Request = io:get_line("Enter 1 to request chat or 2 to go offline: "),
    case {Request} of
            {"1\n"} -> Target = io:get_line("Please enter recipient's username: "),
                       requestChatWith(Client_Node, Target)
            end.

requestChatWith(Client_Node,Recipient) ->
    hw5server:findUser(Client_Node,Recipient).

loop(Server) ->
            Online = io:get_line("Enter 1 to go online: "),
            case {Online} of
                    {"1\n"} -> Name = io:get_line("Please enter a username: "),
                               goOnline(self(), Name)
            end,
            receive
            {_, Message} ->
                    io:format("~p",[Message]),
                    loop(Server)
end.

Answer 1

由于Erlang不维护任何类型的全局状态，因此userList变量将在checkUser/2结束时销毁。

如果要将列表存储在内存中，则需要某种方法来保存列表。 Erlang的内置ets（http://www.erlang.org/doc/man/ets.html）是一个开始寻找的好地方（还有dets和mnesia）。

您也可以在客户端和checkUser/2函数之间传递列表。

Answer 2

我是dethtron5000写的第二个，但是我想指出这是OTP gen_server试图解决的确切情况。您可以将userList保持在请求之间的状态，并使用gen_server API来处理实例化和传入消息。

查找注册过程Erlang

2 个答案: