Commit chapter 12 stuff from last night.

pe/chapter12.erl

@@ -0,0 +1,32 @@
+-module(chapter12).
+-compile(exportall).
+-export([start/2, registrar/0]).
+
+registrar(Client, {Name, Fun}) ->
+    case whereis(Name) of
+	undefined ->
+	    Pid = spawn(Fun),
+	    register(Name, Pid),
+	    Client ! {ok, Name, Pid};
+	Pid -> Client ! {error, exists, Pid}
+    end.
+
+registrar() ->
+    receive
+	{Client, {Name, Fun}} ->
+	    registrar(Client, {Name, Fun}),
+	    registrar();
+	X -> io:format("Spurious message ~w received~n", [X])
+    end.
+
+start(AnAtom, Fun) ->
+    %% start the registrar if it's not been started.
+    case whereis(registrar_proc) of
+	undefined ->
+	    Pid = spawn(chapter12, registrar, []),
+	    register(registrar_proc, Pid);
+	_ -> void
+    end,
+    registrar_proc ! {self(), {AnAtom, Fun}},
+    receive X -> X end.
+	    

pe/processes.erl

@@ -0,0 +1,29 @@
+-module(processes).
+-export([max/1]).
+
+%% max(N)
+%%
+%% Create N processes then destroy them
+%% See how much time this takes
+max(N) ->
+    Max = erlang:system_info(process_limit),
+    RealN = if N > Max -> Max; true -> N end,
+    io:format("Max allowed processes: ~p~n", [Max]),
+    statistics(runtime),
+    statistics(wall_clock),
+    L = for(1, RealN, fun() -> spawn(fun() -> wait() end) end),
+    {_, Time1} = statistics(runtime),
+    {_, Time2} = statistics(wall_clock),
+    lists:foreach(fun(Pid) -> Pid ! die end, L),    
+    U1 = Time1 * 1000 / RealN,
+    U2 = Time2 * 1000 / RealN,
+    io:format("Process spawn time=~p (~p) microseconds~n", [U1, U2]).
+
+wait() ->
+    receive
+	die->
+	    void
+    end.
+
+for(N, N, F) -> [F()];
+for(I, N, F) -> [F()|for(I+1, N, F)].