在不同的终端窗口上运行Erlang程序时的异常

Question

我正在用Erlang开发一个简单的框架来处理2人回合制游戏。 代码如下：

-module(game).
-export([start_server/0,generate_server/0,add_player/0,remove_player/0]).


generate_server() ->
Table_num = 0,
Player_num = 0,
io:format("Server generated...~n", []),
io:format("The current number of tables is ~w~n", [Table_num]),
io:format("The current number of players is ~w~n", [Player_num]),
receive
    login ->
        io:format("A new player has connected!~n", []),
        New = Player_num + 1,
        io:format("The current number of players is ~w~n", [New]);
    logout ->
        io:format("You have beeen succesfully disconnected~n", [])
end.



start_server() ->
    io:format("Welcome player!~nInitializing game...~n", []),
    io:format("Generating server...~n", []),
    register(server,spawn(game, generate_server, [])).


add_player() ->
    server ! login.


remove_player() ->
    server ! logout.

运行此代码时，有两个主要问题：

1. 当我执行add_player（）然后执行remove_player（）时，第二个函数崩溃，但出现异常
2. 如果我在一个终端窗口上启动程序，然后在第二个终端窗口上执行add_player（），则会收到错误消息。 我应该怎么做才能在多个终端窗口上运行它？

任何帮助将不胜感激。

Answer 1

1 /您的服务器中没有环路。 当您启动它时，在进行一些打印后，它会等待receive语句。

收到登录消息后，将执行操作，然后完成服务器代码。 该进程死亡，并且未注册。 所有变量消失，虚拟机清理内存...

因此，稍后，由于您使用的名称不再注册，因此向服务器发送消息的任何进程都将崩溃。

为了使它起作用，您应该保留一个已连接播放器的列表（例如在列表中），并使用该列表作为参数来调用服务器循环。

generate_server(Tlist,Plist) ->
io:format("The current number of tables is ~w~n", [length(Tlist)]),
io:format("The current number of players is ~w~n", [length(Plist)]),
receive
    {login,Name} ->
        io:format("A new player ~p has connected!~n", [Name]),
        generate_server(Tlist,[Name|Plist]);
    {logout,Name} ->
        io:format("You have beeen succesfully disconnected~n", []),
        generate_server(Tlist,lists:delete(Name,Plist))
end.

而对generate_server的调用是由

register(server,spawn(game, generate_server, [[],[]]))

2 /为了在2个不同的节点之间使用erlang消息，您需要：

• 共享相同的Erlang Coockie
• 发现节点（例如使用netadm）
• 获取服务器pid或使用golbal注册名称

请参见http://learnyousomeerlang.com/distribunomicon#alone-in-the-dark中的示例

Answer 2

您错过了服务器的loop主体。 由于服务器仅收到一条消息并退出，因此程序崩溃。 请考虑以下服务器的另一个版本：

generate_server() ->
    Table_num = 0,
    Player_num = 0,
    io:format("Server generated...~n", []),
    io:format("The current number of tables is ~w~n", [Table_num]),
    io:format("The current number of players is ~w~n", [Player_num]),
    loop([]).

loop(Players)->
    receive
        {From,{login,PlayerId}} ->
            io:format("A new player has connected!~n", []),
            io:format("The current number of players is ~w~n", [New]),
            NewPlayers = case lists:member(PlayerId,Players) of
                            true ->
                                From ! {login_failed,exists},
                                Players;
                            false -> 
                                From ! {login_success,true},
                                [PlayerId|Players]
                        end,
            loop(NewPlayers);
        {From,{logout,PlayerId}} ->
            NewPlayers = case lists:member(PlayerId,Players) of
                            true ->
                                From ! {logout,ok},
                                Players -- [PlayerId];
                            false -> 
                                From ! {logout,failed},
                                Players
                        end,
            loop(NewPlayers);
        _ -> loop(Players)
    end.

那里; 看起来好多了。