在不同的終端窗口上運行Erlang程序時的例外情況

Question

我正在Erlang開發一個簡單的框架來處理2人玩家回合制遊戲。該代碼是下面的：

-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. 

有兩個主要的問題，當運行此代碼：

1. 當我執行add_player（），然後remove_player（），該第二功能崩潰與異常
2. 如果我在一個終端窗口上啓動程序，然後在第二個終端窗口上執行add_player（），則會出現錯誤。我應該怎麼做才能在多個終端窗口上運行它？

任何幫助將不勝感激。

Answer 1

1/ 服務器中沒有環路。當你啓動它時，在一些打印之後，它等待接收語句。

當它收到登錄消息時，它執行操作，然後服務器代碼完成;該進程死亡並且未註冊。所有的變量消失，虛擬機清理內存......

所以，以後，任何向服務器發送消息的進程都會崩潰，因爲您使用的是不再註冊的名稱。

爲了使其工作，您應該保留一個連接的球員列表（例如列表中），並以此列表爲參數調用服務器環路。

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. 

，並調用generate_server由

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

2/ 爲了使用2個不同節點之間的Erlang消息來進行，你需要：

• 共享相同的Erlang coockie
• 發現節點（例如使用netadm）
• 得到服務器的PID或使用註冊如果看不到名字

見例如在http://learnyousomeerlang.com/distribunomicon#alone-in-the-dark

Answer 2

你錯過了一個loop體服務器。您的程序崩潰，因爲服務器只收到一條消息並退出。考慮下面的服務器的另一個版本：

 
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. 

那裏;看起來好多了。