gistfile1.hrl

-module(counter_with_locks).
-compile(export_all).


start_counter() ->
	Pid = spawn(?MODULE, counter_loop, [0]),
	register(counter, Pid).

counter_loop(N) ->
	receive 
		{lock, Pid} -> counter_locked(Pid, N);
		value -> io:format("Value = ~w~n", [N])
	end.

counter_locked(Pid, N) ->
	receive 
		{inc, Pid} -> counter_locked(Pid, N+1);
		{unlock, Pid} -> counter_loop(N)
	end.

proc() ->
	Pid = self(),
	counter ! {lock, Pid},
	counter ! {inc, Pid},
	counter ! {unlock, Pid},
	receive
		{halt, Parent} -> Parent ! {halted, Pid}
	end.


sync([]) -> ok;
sync([Pid|Pids]) ->
	Pid ! {halt, self()},
	receive 
		{halted, Pid} -> sync(Pids)
	end.

run() ->
	start_counter(),
	N = lists:seq(1, 1000000),
	Pids = lists:map(fun(_) -> spawn(fun proc/0) end, N),
	sync(Pids),
	counter ! value,
	ok.