Erlang 增加健壮性后的完整示例

由 Loen 创建，路飞 最后一次修改 2016-08-12 增加健壮性后的完整示例让我们改进 Messager 程序以增加该程序的健壮性： %%% Message passing utility. %%% User interface:%%% login(Name)%%% One user at a time can log in from each Erlang node in the%%% system messenger: and choose a suitable Name. If the Name%%% is already logged in at another node or if someone else is%%% already logged in at the same node, login will be rejected%%% with a suitable error message.%%% logoff()%%% Logs off anybody at that node%%% message(ToName, Message)%%% sends Message to ToName. Error messages if the user of this %%% function is not logged on or if ToName is not logged on at%%% any node.%%%%%% One node in the network of Erlang nodes runs a server which maintains%%% data about the logged on users. The server is registered as "messenger"%%% Each node where there is a user logged on runs a client process registered%%% as "mess_client" %%%%%% Protocol between the client processes and the server%%% ----------------------------------------------------%%% %%% To server: {ClientPid, logon, UserName}%%% Reply {messenger, stop, user_exists_at_other_node} stops the client%%% Reply {messenger, logged_on} logon was successful%%%%%% When the client terminates for some reason%%% To server: {'EXIT', ClientPid, Reason}%%%%%% To server: {ClientPid, message_to, ToName, Message} send a message%%% Reply: {messenger, stop, you_are_not_logged_on} stops the client%%% Reply: {messenger, receiver_not_found} no user with this name logged on%%% Reply: {messenger, sent} Message has been sent (but no guarantee)%%%%%% To client: {message_from, Name, Message},%%%%%% Protocol between the "commands" and the client%%% ---------------------------------------------- %%%%%% Started: messenger:client(Server_Node, Name)%%% To client: logoff%%% To client: {message_to, ToName, Message}%%%%%% Configuration: change the server_node() function to return the%%% name of the node where the messenger server runs-module(messenger).-export([start_server/0, server/0, logon/1, logoff/0, message/2, client/2]).%%% Change the function below to return the name of the node where the%%% messenger server runsserver_node() -> messenger@super.%%% This is the server process for the "messenger"%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]server() -> process_flag(trap_exit, true), server([]).server(User_List) -> receive {From, logon, Name} -> New_User_List = server_logon(From, Name, User_List), server(New_User_List); {'EXIT', From, _} -> New_User_List = server_logoff(From, User_List), server(New_User_List); {From, message_to, To, Message} -> server_transfer(From, To, Message, User_List), io:format("list is now: ~p~n", [User_List]), server(User_List) end.%%% Start the serverstart_server() -> register(messenger, spawn(messenger, server, [])).%%% Server adds a new user to the user listserver_logon(From, Name, User_List) -> %% check if logged on anywhere else case lists:keymember(Name, 2, User_List) of true -> From ! {messenger, stop, user_exists_at_other_node}, %reject logon User_List; false -> From ! {messenger, logged_on}, link(From), [{From, Name} | User_List] %add user to the list end.%%% Server deletes a user from the user listserver_logoff(From, User_List) -> lists:keydelete(From, 1, User_List).%%% Server transfers a message between userserver_transfer(From, To, Message, User_List) -> %% check that the user is logged on and who he is case lists:keysearch(From, 1, User_List) of false -> From ! {messenger, stop, you_are_not_logged_on}; {value, {_, Name}} -> server_transfer(From, Name, To, Message, User_List) end.%%% If the user exists, send the messageserver_transfer(From, Name, To, Message, User_List) -> %% Find the receiver and send the message case lists:keysearch(To, 2, User_List) of false -> From ! {messenger, receiver_not_found}; {value, {ToPid, To}} -> ToPid ! {message_from, Name, Message}, From ! {messenger, sent} end.%%% User Commandslogon(Name) -> case whereis(mess_client) of undefined -> register(mess_client, spawn(messenger, client, [server_node(), Name])); _ -> already_logged_on end.logoff() -> mess_client ! logoff.message(ToName, Message) -> case whereis(mess_client) of % Test if the client is running undefined -> not_logged_on; _ -> mess_client ! {message_to, ToName, Message}, okend.%%% The client process which runs on each user nodeclient(Server_Node, Name) -> {messenger, Server_Node} ! {self(), logon, Name}, await_result(), client(Server_Node).client(Server_Node) -> receive logoff -> exit(normal);