diff --git a/async.lua b/async.lua
index 77f6f55..50b05f8 100644
--- a/async.lua
+++ b/async.lua
@@ -1,6 +1,11 @@
 --[[
 	simple kernel for async tasks running in the background
 	
+	can "stall" a task by yielding the string "stall"
+		this will suspend the coroutine until the rest of
+		the queue has been processed or stalled
+		and can early-out update_for_time
+
 	todo: 
 		multiple types of callbacks
 			finish, error, step
@@ -15,6 +20,7 @@ async._mt = {__index = async}
 function async:new()
 	return setmetatable({
 		tasks = {},
+		tasks_stalled = {},
 	}, self._mt)
 end
 
@@ -33,7 +39,14 @@ function async:update()
 	--grab task definition
 	local td = table.remove(self.tasks, 1)
 	if not td then
-		return false
+		--have we got stalled tasks to re-try?
+		if #self.tasks_stalled > 0 then
+			--swap queues rather than churning elements
+			self.tasks_stalled, self.tasks = self.tasks, self.tasks_stalled
+			td = table.remove(self.tasks, 1)
+		else
+			return false
+		end
 	end
 	--run a step
 	local co, args, cb, error_cb = td[1], td[2], td[3], td[4]
@@ -54,23 +67,61 @@ function async:update()
 	--check done
 	if coroutine.status(co) == "dead" then
 		--done? run callback with result
-		cb(a, b, c, d, e, f, g, h)
+		if cb then
+			cb(a, b, c, d, e, f, g, h)
+		end
 	else
-		--if not done, re-add
-		table.insert(self.tasks, td)
+		--if not completed, re-add to the appropriate queue
+		if a == "stall" then
+			--add to stalled queue as signalled stall
+			table.insert(self.tasks_stalled, td)
+		else
+			table.insert(self.tasks, td)
+		end
 	end
 
 	return true
 end
 
 --update tasks for some amount of time
-function async:update_for_time(t)
+function async:update_for_time(t, early_out_stalls)
 	local now = love.timer.getTime()
 	while love.timer.getTime() - now < t do
 		if not self:update() then
 			break
 		end
+		--all stalled?
+		if early_out_stalls and #self.tasks == 0 then
+			break
+		end
 	end
 end
 
+--add a function to run after a certain delay (in seconds)
+function async:add_timeout(f, delay)
+	local trigger_time = love.timer.getTime() + delay
+	self:call(function()
+		while love.timer.getTime() < trigger_time do
+			coroutine.yield("stall")
+		end
+		f()
+	end)
+end
+
+--add a function to run repeatedly every delay (in seconds)
+--note: not super useful currently unless you plan to destroy the async object
+--		as there's no way to remove tasks :)
+function async:add_interval(f, delay)
+	local trigger_time = love.timer.getTime() + delay
+	self:call(function()
+		while true do
+			while love.timer.getTime() < trigger_time do
+				coroutine.yield("stall")
+			end
+			f()
+			trigger_time = trigger_time + delay
+		end
+	end)
+end
+
 return async
\ No newline at end of file