tcp_server.erl注解

java 代码

%% Copyright (C) 2002, Joe Armstrong
%% File    : tcp_server.erl
%% Author  : Joe Armstrong (joe@sics.se)
%% Purpose : Keeps track of a number of TCP sessions
%% Last modified: 2002-11-17

-module(tcp_server).

-export([start_raw_server/4, start_client/3,
     stop/1, children/1]).

-define(KILL_DELAY, 1000).

%% -export([start_child/3]).

%% start_raw_server(Port, Fun, Max)
%%   This server accepts up to Max connections on Port
%%   The *first* time a connection is made to Port
%%   Then Fun(Socket) is called.
%%   Thereafter messages to the socket result in messsages to the handler.

%% a typical server is usually written like this:

%% To setup a lister

%% start_server(Port) ->
%%     S = self(),
%%     process_flag(trap_exit, true),
%%     tcp_server:start_raw_server(Port,
%%              fun(Socket) -> input_handler(Socket, S) end,
%%              15,
%%                              0)
%%     loop().

%% The loop() process is a central controller that all
%% processes can use to synchronize amongst themselfves if necessary
%% It ends up as the variable "Controller" in the input_handler

%% A typical server is written like this:

%% input_handler(Socket, Controller) ->
%%     receive
%%  {tcp, Socket, Bin} ->
%%      ...
%%      gen_tcp:send(Socket, ...)
%%
%%  {tcp_closed, Socket} ->
%%
%%
%%  Any ->
%%      ...
%%
%%     end.

start_client(Host, Port, Length) ->
     gen_tcp:connect(Host, Port,
             [binary,
              {active, true},
              {packet, 2},
              {packet_size, Length}], 30000).

%% Note when start_raw_server returns, it should be ready to
%% Immediately accept connections
%% 作用
%%      当start_raw_server返回时, 就可以接受连接啦
%% 参数
%%      Port    服务器监听端口
%%      Fun     数据处理函数
%%      Max     最大连接数
%%      Length  最大包的长度
start_raw_server(Port, Fun, Max, Length) ->
    Name = port_name(Port), % 用端口号来命名进程
    case whereis(Name) of
    undefined ->            % 如果端口还未定义的话，则启动
        Self = self(),
        Pid = spawn_link(fun() ->   % 产生一个新进程
                     cold_start(Self, Port, Fun, Max, Length)   % 冷启动
                 end),
        receive
        {Pid, ok} ->
            register(Name, Pid), % 接收到
            {ok, Pid};
        {Pid, Error} ->
            Error
        end;
    _Pid ->             % 如果端口已定义，则报错
        {error, already_started}
    end.

stop(Port) when integer(Port) ->
    Name = port_name(Port),
    case whereis(Name) of
    undefined ->
        not_started;
    Pid ->
        exit(Pid, kill),
        (catch unregister(Name)),
        stopped
    end.

children(Port) when integer(Port) ->
    port_name(Port) ! {children, self()},   %
    receive
    {session_server, Reply} -> Reply
    end.

%% 作用
%%      以端口号做为服务名称
%% 参数
%%      端口号
port_name(Port) when integer(Port) ->
    list_to_atom("portServer" ++ integer_to_list(Port)).

%% 作用
%%      启动服务
%%  参数
%%      Master      所有者
%%      Port        端口
%%      Fun         处理函数
%%      Max         数大连接数
%%      Length      最大包的长度
cold_start(Master, Port, Fun, Max, Length) ->
    process_flag(trap_exit, true),  % 设置退出陷阱
    io:format("Starting a port server on ~p...~n",[Port]),
    % 绑定到端口,进行监听
    case gen_tcp:listen(Port, [binary,
                   %% {dontroute, true},
                   {nodelay,true},
                   {packet_size, Length},
                   {packet, 2},
                   {backlog, 1024},
                   {reuseaddr, true},
                   {active, false}]) of
    {ok, Listen} ->
        %% io:format("Listening on:~p~n",[Listen]),
        Master ! {self(), ok},  % 发送成功消息
        New = start_accept(Listen, Fun), % 开始接受连接
        %% Now we're ready to run
        socket_loop(Listen, New, [], Fun, Max); % 接受连接后,开始网络通信了
    Error ->
        Master ! {self(), Error}
    end.

%% Don't mess with the following code uless you really know what you're
%% doing (and Thanks to Magnus for heping me get it right)
%% 作用
%%      接受连接后，开始运作
socket_loop(Listen, New, Active, Fun, Max) ->
    receive
    {istarted, New} ->
        Active1 = [New|Active], % 参见start_child,把新连接加入到活动列表中
        possibly_start_another(false, Listen, Active1, Fun, Max);
    {'EXIT', New, _Why} ->
        %%io:format("Child exit=~p~n",[Why]),
        possibly_start_another(false, Listen, Active, Fun, Max);
    {'EXIT', Pid, _Why} ->
        %%io:format("Child exit=~p~n",[Why]),
        Active1 = lists:delete(Pid, Active),
        possibly_start_another(New, Listen, Active1, Fun, Max);
    {children, From} ->
        From ! {session_server, Active},
        socket_loop(Listen, New, Active, Fun, Max);
    Other ->
        io:format("Here in loop:~p~n",[Other])
    end.

possibly_start_another(New, Listen, Active, Fun, Max) when pid(New) ->
    socket_loop(Listen, New, Active, Fun, Mzax);
possibly_start_another(false, Listen, Active, Fun, Max) ->
    case length(Active) of
    N when N < Max ->
        New = start_accept(Listen, Fun),
        socket_loop(Listen, New, Active, Fun, Max);
    _ ->
        error_logger:warning_report(
          [{module, ?MODULE},
           {line, ?LINE},
           {message, "Connections maxed out"},
           {maximum, Max},
           {connected, length(Active)},
           {now, now()}]),
        socket_loop(Listen, false, Active, Fun, Max)
    end.

%% 作用
%%      开始接受连接啦
%% 参数
%%      Listen  监听的Socket
%%      Fun     数据处理函数
start_accept(Listen, Fun) ->
    S = self(),
    spawn_link(fun() -> start_child(S, Listen, Fun) end). % 一个进程处理一个连接

start_child(Parent, Listen, Fun) ->
    case gen_tcp:accept(Listen) of  % 接受一个连接
    {ok, Socket} ->
        Parent ! {istarted,self()}, % 参见socket_loop, tell the controller
        inet:setopts(Socket, [{nodelay,true},
                  {packet, 2},
                  {active, true}]), % before we activate socket
        Fun(Socket); % 这里应用了数据处理函数Fun
    _Other ->
        exit(oops)
    end.