有意思的一段代码：
1 %%% Message passing utility.
2 %%% User interface:
3 %%% logon(Name)
4 %%% One user at a time can log in from each Erlang node in the
5 %%% system messenger: and choose a suitable Name. If the Name
6 %%% is already logged in at another node or if someone else is
7 %%% already logged in at the same node, login will be rejected
8 %%% with a suitable error message.
9 %%% logoff()
10 %%% Logs off anybody at that node
11 %%% message(ToName, Message)
12 %%% sends Message to ToName. Error messages if the user of this
13 %%% function is not logged on or if ToName is not logged on at
14 %%% any node.
15 %%%
16 %%% One node in the network of Erlang nodes runs a server which maintains
17 %%% data about the logged on users. The server is registered as "messenger"
18 %%% Each node where there is a user logged on runs a client process registered
19 %%% as "mess_client"
20 %%%
21 %%% Protocol between the client processes and the server
22 %%% ----------------------------------------------------
23 %%%
24 %%% To server: {ClientPid, logon, UserName}
25 %%% Reply {messenger, stop, user_exists_at_other_node} stops the client
26 %%% Reply {messenger, logged_on} logon was successful
27 %%%
28 %%% To server: {ClientPid, logoff}
29 %%% Reply: {messenger, logged_off}
30 %%%
31 %%% To server: {ClientPid, logoff}
32 %%% Reply: no reply
33 %%%
34 %%% To server: {ClientPid, message_to, ToName, Message} send a message
35 %%% Reply: {messenger, stop, you_are_not_logged_on} stops the client
36 %%% Reply: {messenger, receiver_not_found} no user with this name logged on
37 %%% Reply: {messenger, sent} Message has been sent (but no guarantee)
38 %%%
39 %%% To client: {message_from, Name, Message},
40 %%%
41 %%% Protocol between the "commands" and the client
42 %%% ----------------------------------------------
43 %%%
44 %%% Started: messenger:client(Server_Node, Name)
45 %%% To client: logoff
46 %%% To client: {message_to, ToName, Message}
47 %%%
48 %%% Configuration: change the server_node() function to return the
49 %%% name of the node where the messenger server runs
50
51 -module(messenger).
52 -export([start_server/0, server/1, logon/1, logoff/0, message/2, client/2]).
53
54 %%% Change the function below to return the name of the node where the
55 %%% messenger server runs
56 server_node() ->
57 % [email protected]
58 [email protected]
59 % erlang:node().
60
61 %%% This is the server process for the "messenger"
62 %%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]
63 server(User_List) ->
64 receive
65 {From, logon, Name} ->
66 New_User_List = server_logon(From, Name, User_List),
67 server(New_User_List);
68 {From, logoff} ->
69 New_User_List = server_logoff(From, User_List),
70 server(New_User_List);
71 {From, message_to, To, Message} ->
72 73 server_transfer(From, To, Message, User_List),
74 io:format("list is now: ~p~n", [User_List]),
75 server(User_List)
76 end.
77
78 %%% Start the server
79 start_server() ->
80 register(messenger, spawn(messenger, server, [[]])).
81
82 %%% Server adds a new user to the user list
83 server_logon(From, Name, User_List) ->
84 %% check if logged on anywhere else
85 case lists:keymember(Name, 2, User_List) of
86 true ->
87 From ! {messenger, stop, user_exists_at_other_node}, %reject logon
88 User_List;
89 false ->
90 From ! {messenger, logged_on},
91 [{From, Name} | User_List]
92 end.
93
94 %%% Server deletes a user from the user list
95 server_logoff(From, User_List) ->
96 lists:keydelete(From, 1, User_List).
97
98 %add user to the list
99 %%% Server transfers a message between user
100 server_transfer(From, To, Message, User_List) ->
101 %% check that the user is logged on and who he is
102 case lists:keysearch(From, 1, User_List) of
103 false ->
104 From ! {messenger, stop, you_are_not_logged_on};
105 {value, {From, Name}} ->
106 server_transfer(From, Name, To, Message, User_List)
107 end.
108
109 %%% If the user exists, send the message
110 server_transfer(From, Name, To, Message, User_List) ->
111 %% Find the receiver and send the message
112 case lists:keysearch(To, 2, User_List) of
113 false ->
114 From ! {messenger, receiver_not_found};
115 {value, {ToPid, To}} ->
116 ToPid ! {message_from, Name, Message},
117 From ! {messenger, sent}
118 end.
119
120 %%% User Commands
121 logon(Name) ->
122 case whereis(mess_client) of
123 undefined ->
124 125 register(mess_client,
126 spawn(messenger, client, [server_node(), Name]));
127 _ -> already_logged_on
128 end.
129
130 logoff() ->
131 mess_client ! logoff.
132
133 message(ToName, Message) ->
134 case whereis(mess_client) of % Test if the client is running
135 undefined ->
136 not_logged_on;
137 _ -> mess_client ! {message_to, ToName, Message},
138 139 ok
140 end.
141
142 %%% The client process which runs on each server node
143 client(Server_Node, Name) ->
144 {messenger, Server_Node} ! {self(), logon, Name},
145 await_result(),
146 client(Server_Node).
147
148 client(Server_Node) ->
149 150 receive
151 logoff ->
152 {messenger, Server_Node} ! {self(), logoff},
153 exit(normal);
154 {message_to, ToName, Message} ->
155156 {messenger, Server_Node} ! {self(), message_to, ToName, Message},
157 await_result();
158 {message_from, FromName, Message} ->
159 io:format("Message from ~p: ~p~n", [FromName, Message])
160 end,
161 client(Server_Node).
162
163 %%% wait for a response from the server
164 await_result() ->
165 receive
166 {messenger, stop, Why} -> % Stop the client
167 io:format("~p~n", [Why]),
168 exit(normal);
169 {messenger, What} -> % Normal response
170 io:format("~p~n", [What])
171 end.
其中
server_node()代码必须全局固定。
这是服务端：
([email protected])131>
([email protected])131> messenger:start_server().
true
([email protected])132>
([email protected])132>
([email protected])132> messenger:logon(frank).
logged_on
true
([email protected])133>
([email protected])133>
([email protected])135> messenger:message(mini, "123.123.123.").
list is now: [{<10396.45.0>,mini},{<0.333.0>,frank}]
sent
ok
([email protected])136>
([email protected])136>
这是客户端：
([email protected])2> messenger:logon(mini). true logged_on ([email protected])3> ([email protected])3> ([email protected])6> ([email protected])6> ([email protected])6> Message from frank: "123.123.123." ([email protected])6>
ending 。。。。。。
时间： 2024-08-26 07:41:18