Programming Erlang, Problem 8.11

ring.erl

-module(ring).
-export([body/2]).

for(N,N,F) -> [F()];
for(I,N,F) -> [F()|for(I+1,N,F)].

for1(N,N,F) -> [F(N)];
for1(I,N,F) -> [F(I)|for1(I+1,N,F)].

baton() ->
	receive
		{set, Next, Incr} ->
			baton(Next,Incr);
		{baton,_J,_M} ->
			io:format("I don't know the next one.~n"),
			baton()
	end.

baton(Next,false) ->
	receive
		Any ->
			% io:format(" -"),
			Next ! Any,
			baton(Next,false)
	end;
baton(Next,true) ->
	receive
		{baton,Caller,M,M} ->
			% io:format(" +|~n"),
			Caller ! done;
		{baton,Caller,J,M} ->
			% io:format(" +~n"),
			Next ! {baton,Caller,J+1,M},
			baton(Next,true)
	end.

body(N,M) ->
	statistics(runtime),
	statistics(wall_clock),
	Batons = for(1,N,fun() -> spawn(fun baton/0) end),
	for1(1,N,
		 fun(I) ->
				 Ith = lists:nth(I,Batons),
				 Next = lists:nth((I rem N)+1,Batons),
				 Ith ! {set,Next,I==N}
         end),

    [First|_] = Batons,
	{_, Time1} = statistics(runtime),
	{_, Time2} = statistics(wall_clock),
	io:format("Preparation time=~p (~p) msec~n", [Time1, Time2]),

	statistics(runtime),
	statistics(wall_clock),
    First ! {baton,self(),1,M},
	receive
		done ->
			{_, Time3} = statistics(runtime),
			{_, Time4} = statistics(wall_clock),
			io:format("Process time=~p (~p) msec~n", [Time3, Time4])
	end.

ring2.erl

-module(ring).
-export([body/2]).

for(N,N,F) -> [F()];
for(I,N,F) -> [F()|for(I+1,N,F)].

for1(N,N,F) -> [F(N)];
for1(I,N,F) -> [F(I)|for1(I+1,N,F)].

baton() ->
	receive
		{set, Next, Caller, Incr} ->
			baton(Next,Caller,Incr);
		{baton,_J,_M} ->
			io:format("I don't know the next one.~n"),
			baton()
	end.

baton(Next,Caller,false) ->
	receive
		Any ->
			% io:format(" -"),
			Next ! Any,
			baton(Next,Caller,false)
	end;
baton(Next,Caller,true) ->
	receive
		{baton,M,M} ->
			% io:format(" +|~n"),
			Caller ! done;
		{baton,J,M} ->
			% io:format(" +~n"),
			Next ! {baton,J+1,M},
			baton(Next,Caller,true)
	end.

body(N,M) ->
	statistics(runtime),
	statistics(wall_clock),
	Batons = for(1,N,fun() -> spawn(fun baton/0) end),
	Caller = self(),
	for1(1,N,
		 fun(I) ->
				 Ith = lists:nth(I,Batons),
				 Next = lists:nth((I rem N)+1,Batons),
				 Ith ! {set,Next,Caller,I==N}
         end),

    [First|_] = Batons,
	{_, Time1} = statistics(runtime),
	{_, Time2} = statistics(wall_clock),
	io:format("Preparation time=~p (~p) msec~n", [Time1, Time2]),

	statistics(runtime),
	statistics(wall_clock),
    First ! {baton,1,M},
	receive
		done ->
			{_, Time3} = statistics(runtime),
			{_, Time4} = statistics(wall_clock),
			io:format("Process time=~p (~p) msec~n", [Time3, Time4])
	end.