Erlang-实现进程环

M是消息传递数目，N进程数量，Msg是传递的消息

-module(exe3_2).
-export([start/3,stop/0]).

start(M,N,Msg) ->register(ring,spawn(fun()->ring_service(M,N,Msg) end)).

stop() -> ring!stop.

ring_service(M,N,Msg) ->
    Ring=ring_node(N,[]),%Ring是进程环
    send_msg(M,Msg,Ring),
    receive
        stop -> stop_ring(Ring)
    end.

stop_ring([]) ->ok;
stop_ring([H|T]) ->H!stop,
                 stop_ring(T).

send_msg(0,_Msg,_Ring) ->ok;
send_msg(M,Msg,[H|T]) ->H ! {msg,M,Msg},
                        send_msg(M-1,Msg,T ++ [H]).

ring_node(N,Ring) when N>0
                    ->Next_Pid = spawn(fun() ->loop() end),
                    ring_node(N-1,[Next_Pid|Ring]);
ring_node(0,Ring) ->lists:reverse(Ring).

loop() ->
        receive
            {msg,M,Msg} ->
                io:format("~w:~w:~w~n",[self(),M,Msg]),
                loop();
            stop ->true
        end.