class TimedRateLimiter;
	# not completely reliable if called from multiple threads
	# rate is unit per second
	def initialize rate, max, credit;
		@rate, @max = rate, max;
		0 < rate or fail "invalid rate for TimedRateLimiter";
		0 < max or fail "invalid max for TimedRateLimiter";
		@time = Time.now;
		@tally = if credit < 0; 0 else credit end;
		@lock = Mutex.new;
	end;
	def update;
		time = Time.now;
		@tally += (time - @time) * @rate;
		if @max < @tally; @tally = @max; end;
		@time = time;
	end;
	def consume amt = 1;
		slp = ();
		@lock.synchronize do
			0 <= amt or 
				amt = 0;
			update;
			if @tally < amt;
				slp = Float(amt - @tally) / @rate;
			end;
		end;
		if slp 
			sleep slp;
		end;
		@lock.synchronize do
			@tally -= amt;
		end;
		true;
	end;
	def try_consume amt = 1;
		r = false;
		@lock.synchronize do
			0 <= amt or 
				amt = 0;
			update;
			if amt <= @tally;
				@tally -= amt;
				r = true;
			end;
		end;
		r;
	end;
end;

##</code><code>##

@request_limiter = TimedRateLimiter.new 3, 3, 1;

##</code><code>##

@request_limiter.consume;