Newbie - First program - controlling nuclear reactors

Hi everyone, I'm used to programming in several languages so in general I'm comfortable coding, but not completely knowledgeable in lua. Anyway I figured a good way to learn some computer-craft was to replace my complicated redstone setup controlling multiple nuclear reactors, with a computer-craft system. I figured a good way to do this would be each reactor would have a computer, which would do two things, it would monitor for messages from a master computer and perform actions based on those messages, and also monitor the state of the reactor, and notify the master controller if something occurs, like a temperature spike. Likewise, the master will listen to messages from the individual reactor computers - say it get's sent an "I'm too hot" message, and then depending on the settings of the master controller it could send a response instruction, like shut down the reactor permanently, or shut down for 5 mins and start up again and so on. So I got coding on the side of the individual reactor computers, a program I'm calling "reactor_slave".

My code is below. We define the monitoring function that sends a message to the master first, then the function that istens and responds to the master's messages, then define some variables for the reactor, and then I figured the parallel.waitForAny function would allow me to run these two functions, responding to master messages, and sending messages to master, at the same time:

--Continually checks the reactor's temperature.
function checkReactor()
while true do
  if rs.getInput(tempSide) and rs.getOutput(reactorSide) then
		 print("The reactor has a severely high temperature.")
   print("Alerting the control computer...")
   rednet.send(masterID, "TooHot")
  elseif rs.getInput(tempSide) and rs.getOutput(reactorSide) == false then
   print("The reactor is very hot, however it has already been turned off.")
   end
end
end

--Checks for messages from the controller & responds.
function checkMessages()
while true do
  senderID, message = rednet.recieve()
  if senderID == masterID then  
   if message == indshutdown or message == "ALLSHUTDOWN" then
  
							   print("Recieved an order from controller to shutdown, shutting down")
	  
	rs.setOutput(reactorSide, false)
	  
	print("Shutdown the reactor.")
	
		  elseif message == indstartup or message == "ALLSTARTUP" then
				  print("Recieved an order from controller to start up.")
	rs.setOutput(reactorSide, true)
	print("Started up the reactor.")
   end
  end
end
end
--Variables
for individual reactor.
reactorSide = "back"
tempSide = "left"
masterID = 8
indstartup = "startupbreed"
indshutdown = "shutdownbreed"
--Script Body.
rednet.open("top")
rs.setOutput(reactorOutput, false)
parallel.waitForAny(checkReactor, checkMessages)

However if I run this code I get an error to do with the waitForAny function:

parallel:22:reactor_server:6: Too long without yielding.

What am I doing wrong? And how can I simultaneously check reactor status and send messages of status, and also check and do reactions based on messages recieved from the master computer?

Thanks,
Ben.

Your checkReactor function doesn't yield at all. Throw an os.pullEvent("redstone") at the end to wait for redstone changes for each iteration.