Erlang学习：A non-OTP supervisor for a non-OTP server

参考：http://blog.bot.co.za/en/article/349/an-erlang-otp-tutorial-for-beginners#.UpoXamSOGJY

A non OTP server:

%%%---------------------------------------------------------------------------%%% @doc A simple server that does not use OTP.%%% @author Hans Christian v. Stockhausen <hc at vst.io>%%% @end%%%--------------------------------------------------------------------------- -module(no_otp).                     % module name (same as our erl filename,                                     % i.e. no_otp.erl) %% API-export([                            % the functions we export - our API  start/0,                           % - start new server process  stop/0,                            % - stop server  say_hello/0,                       % - print "Hello" to stdout  get_count/0                        % - reply with number of times the main   ]).                                %   loop was executed %% Callbacks-export([init/0]).                   % exported so we can spawn it in start/0                                     % listed as a separate export here as a                                     % hint to clients not to use it -define(SERVER, ?MODULE).            % SERVER macro is an alias for MODULE,                                     % and expands to 'no_otp' -record(state, {count}).             % record for our server state. Rather                                     % arbitrarily we track how often the                                     % main loop is run - see loop/1  %=============================================================================% API - functions that our clients use to interact with the server%============================================================================= start() ->                           % spawn new process that calls init/0    spawn(?MODULE, init, []).          % the new process' PID is returned stop() ->                            % send the atom stop to the process                             ?SERVER ! stop,                    % to instruct our server to shut down  ok.                                % and return ok to caller say_hello() ->                       % send the atom say_hello to the process  ?SERVER ! say_hello,               % to print "Hello" to sdout  ok. get_count() ->                       % send callers Pid and the atom get_count  ?SERVER ! {self(), get_count},     % to request counter value  receive                            % wait for matching response and return    {count, Value} -> Value          % Value to the caller  end.   %=============================================================================% callback functions - not to be used by clients directly%============================================================================= init() ->                            % invoked by start/0  register(?SERVER, self()),         % register new process PID under no_otp  loop(#state{count=0}).             % start main server loop %=============================================================================% internal functions - note, these functions are not exported%============================================================================= loop(#state{count=Count}) ->         % the main server loop  receive Msg ->                     % when API functions send a message    case Msg of                      % check the atom contained      stop ->                        % if atom is 'stop'        exit(normal);                %   exit the process      say_hello ->                   % if atom is 'say_hello'        io:format("Hello~n");        %   write "Hello" to stdout      {From, get_count} ->           % if Msg is tuple {Pid(), get_count}        From ! {count, Count}        % reply with current counter value    end                              %   in tagged tupple {count, Value}  end,  loop(#state{count = Count + 1}).   % recurse with updated state

A non-OTP supervisor

%%%----------------------------------------------------------------------------%%% @doc A non-OTP supervisor%%% @author Hans Christian v. Stockhausen <hc at vst.io>%%% @end%%%-----------------------------------------------------------------------------module(sup).%% API-export([start_server/0]).%% Callbacks-export([supervise/0]).%%=============================================================================%% API%%=============================================================================start_server() ->  spawn(?MODULE, supervise, []).%%=============================================================================%% Callbacks%%=============================================================================supervise() ->  process_flag(trap_exit, true),    % don't crash us but rather send us a                                    %  message when a linked process dies  Pid = no_otp:start(),             % start our server  link(Pid),                        % and link to it  receive {'EXIT', Pid, Reason} ->  % wait for a message that informs us    case Reason of                  %  that our porcess shut down      normal -> ok;                 % if the reason is 'normal' do nothing      _Other -> start_server()      %  otherwise start all over    end  end.

运行：

Eshell V5.8.5  (abort with ^G)1> c(sup).                                   % compile our supervisor module{ok,sup}2> sup:start_server().                       % start the supervisor<0.39.0>                                     % it got the process ID ..39..3> whereis(no_otp).                          % let's find our no_otp process<0.40.0>                                     % it got ..40..4> no_otp:say_hello().                       % let's try to use the APIHello                                        % worksok5> no_otp:get_count().                       % works too 16> no_otp ! crash.                           % time to crash itcrash=ERROR REPORT===Error in process <0.40.0> with exit value:   {{case_clause,crash},[{no_otp,loop,1}]}   % as expected a case_clause error7> no_otp:get_count().                      % but a new process was started0                                           % as we can see here8> no_otp:stop().                           % now let's stop it 'normally'ok9> whereis(no_otp).                         % and check for a new instanceundefined                                   % but there is none. Correct!10>