erlang學習： 基於gen_server的echoserver及監控模組

第一版基礎上，將echoserver融入OTP:gen_server框架
同時引入OPT:supervisor行為包，實現對 echoserver的監控模組

當 echoserver退出後，監控模組master可以重啟之。

erlang的監控樹絕對是精華所在，解決了分散式開發的一個重要的問題域

-module(es2).
-behavior(gen_server).

-export([start_link/0, stop/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
-export([server_loop/2, handle_connect/3]).

start_link() ->
	gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

stop() ->
	gen_server:cast(?MODULE, stop).

init([]) ->
	process_flag(trap_exit, true),
	io:format("~p starting, ~p~n", [?MODULE, self()]),
	{ok, ListenSocket} = gen_tcp:listen(1234, [binary, {reuseaddr, true}, {active, false}]),
	register(echoserver, spawn(?MODULE, server_loop, [ListenSocket, 0])), 
	{ok, 0}.

terminate(_Reason, N) ->
	io:format("~p stopping, ~p~n", [?MODULE, self()]),
	ok.

handle_call(_Request, _From, _State) ->
	{reply, 0, _State}.

handle_cast(stop, N) ->
	echoserver ! {quit},
	{stop, normal, N};
handle_cast(_Msg, N) ->
	{noreply, N}.

handle_info(_Info, N) ->
	{noreply, N}.

code_change(Old, N, Extra) ->
	{ok, N}.


server_loop(ListenSocket, Count) ->
	% 阻塞，等待連線
	receive
		{quit} ->
			io:format("echoserver will stop~n"),
			gen_tcp:close(ListenSocket);
		{'EXIT', Pid, _Reason } ->
			io:format("Child ~p exit~n", [Pid]),
			server_loop(ListenSocket, Count);
		_ ->
			%io:format("recv ~p~n", Reason)
			true
	after 10 -> 
		 case gen_tcp:accept(ListenSocket, 3000) of
		 	{ok, Socket} ->
				% 建立程式?
				spawn(?MODULE, handle_connect, [Socket, [], Count]),
				server_loop(ListenSocket, Count+1);
			{error, timeout} ->
				server_loop(ListenSocket, Count);
			{error, Reason} ->
				io:format("accept failed~n"),
				gen_tcp:close(ListenSocket)
		end
	end.

handle_connect(Socket, BinaryList, Count) ->
	io:format("handle_connect ~p~n", [self()]),	
	case gen_tcp:recv(Socket, 0) of
		{ok, Binary} ->
			% 繼續接收資料
			case gen_tcp:send(Socket, Binary) of
				ok ->
					handle_connect(Socket, BinaryList, Count);
				{error, Reason} -> 
					io:format("send failed~n"),
					gen_tcp:close(Socket)
			end;
		{error, timeout} ->
			io:format("recv timeout~n"),
			gen_tcp:close(Socket);
		{error, closed} ->
			% 直到對端關閉
			io:format("peer closed~n"),
			gen_tcp:close(Socket)
	end.

-module(master).
-behavior(supervisor).

-export([start/0, stop/0, start_monitor/0]).
-export([init/1]).

%% 從shell執行的時候呼叫此函式
start() ->
	%% 建立master程式
	register(master, spawn(?MODULE, start_monitor, [])).

stop() ->
	master ! {quit}.	

start_monitor() ->
	io:format("master started: ~p~n", [self()]),
	%% 建立監控子程式，註冊為monitor，並執行 init/1
	{ok, Pid} = supervisor:start_link({local, monitor}, ?MODULE, []),
	%unlink(Pid),
	wait().

%% monitor程式執行init/1，啟動所有被監控的子程式，並監控這些程式
init(FileName) ->
	io:format("enter init, ~s, ~p~n", [FileName, self()]),
	%% 執行 es2:start_link
	ChildSpec = {es, {es2, start_link, []}, permanent, 2000, worker, [es2]},
	%% 監控規範：被監控程式退出後，重啟之，重啟次數100，重啟間隔10ms
	{ok, {{one_for_one, 100, 10}, [ChildSpec]}}.

%% master程式迴圈等待退出訊息
wait() ->
	receive
		{quit} ->
			io:format("recv quit msg~n");
			%%master程式退出，從而導致monitor及所有monitor的子程式都退出
		{'EXIT', Pid, Reason} ->
			io:format("Child ~p exit~n", [Pid]),
			wait()
	end.