content: {-
  Copyright (c) 2014-2015, Johan Nordlander, Jonas Duregård, Michał Pałka,
                           Patrik Jansson and Josef Svenningsson
  All rights reserved.
  
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  modification, are permitted provided that the following conditions are met:
  
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       this list of conditions and the following disclaimer.
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  -}
  
  {-# LANGUAGE RankNTypes #-}
  module Main where
  
  import Test.QuickCheck.Random
  import ARSim
  import System.Random
  
  r1 pqe          = do sequence_ $ replicate 10 $ rte_send pqe (1::Int)
  
  -- producer adds numbers to the queue.
  producer        = do pqe <- providedQueueElement
                       runnable Concurrent [Init] (r1 pqe)
                       return (seal pqe)
  
  r2 rqe irv      = do Ok x <- rte_receive rqe
                       Ok v <- rte_irvRead irv
                       rte_irvWrite irv (v+x)
                       return ()
  
  -- consumer runs its runnable each time an element is added to the queue.
  -- The runnable takes an element from the queue and adds its value to
  -- its accumulator irv. It has two kinds of race conditions:
  -- * The queue should be empty, but sending messages to it
  --     does not trigger r2 when r2 is already Pending.
  -- * Different instances of r2 clash when they concurrently update
  --     the irv.
  consumer        = component $
                    do irv <- interRunnableVariable (0 :: Int)
                       rqe <- requiredQueueElement 10
                       runnable Concurrent [ReceiveQ rqe] (r2 rqe irv)
                       return (seal rqe)
  
  -- Fixed version of consumer, which eliminates the second race condition.
  consumerEx      = component $
                    do ex <- exclusiveArea
                       irv <- interRunnableVariable (0 :: Int)
                       rqe <- requiredQueueElement 10
                       let r2 = do Ok x <- rte_receive rqe
                                   rte_enter ex
                                   Ok v <- rte_irvRead irv
                                   rte_irvWrite irv (v+x)
                                   rte_exit ex
                                   return ()
                       runnable Concurrent [ReceiveQ rqe] r2
                       return (seal rqe)
  
  -- Version of consumer that fixes both race conditions.
  consumerFix     = component $
                    do ex <- exclusiveArea
                       irv <- interRunnableVariable (0 :: Int)
                       rqe <- requiredQueueElement 10
                       let r2 = do
                              cx <- rte_receive rqe
                              case cx of
                                Ok x -> do
                                  rte_enter ex
                                  Ok v <- rte_irvRead irv
                                  rte_irvWrite irv (v+x)
                                  rte_exit ex
                                  r2
                                NO_DATA -> return ()
                       runnable Concurrent [ReceiveQ rqe] r2
                       return (seal rqe)
  
  test :: AR c (RQ Int ()) -> AR c ()
  test consumerx  = do pqe <- component producer
                       rqe <- consumerx
                       connect pqe rqe
  
  -- Run the buggy version with the randomised scheduler
  main            = mainRand consumer
  
  mainRand :: (forall c. AR c (RQ Int ())) -> IO ()
  mainRand consumerx  = do rng <- newQCGen
                           putStrLn $ "Using seed: " ++ show rng
                           putTrace $ fst $ simulationRand rng (test consumerx)
  
  --
  main1            = putTrace $ fst $ simulationHead (test consumer)
  