dejafu/Test/DejaFu/Deterministic/Schedule.hs

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-- | Deterministic scheduling for concurrent computations.
module Test.DejaFu.Deterministic.Schedule
( Scheduler
, ThreadId
, NonEmpty(..)
-- * Pre-emptive
, randomSched
, roundRobinSched
-- * Non pre-emptive
, randomSchedNP
, roundRobinSchedNP
-- * Utilities
, makeNP
, toList
) where
import Data.List.Extra
import System.Random (RandomGen, randomR)
2015-01-31 18:50:54 +03:00
import Test.DejaFu.Deterministic.Internal
-- | A simple random scheduler which, at every step, picks a random
-- thread to run.
randomSched :: RandomGen g => Scheduler g
randomSched g _ threads = (threads' !! choice, g') where
(choice, g') = randomR (0, length threads' - 1) g
threads' = toList threads
-- | A random scheduler which doesn't pre-empt the running
-- thread. That is, if the last thread scheduled is still runnable,
-- run that, otherwise schedule randomly.
randomSchedNP :: RandomGen g => Scheduler g
randomSchedNP = makeNP randomSched
-- | A round-robin scheduler which, at every step, schedules the
-- thread with the next 'ThreadId'.
roundRobinSched :: Scheduler ()
roundRobinSched _ prior threads
| prior >= maximum threads' = (minimum threads', ())
| otherwise = (minimum $ filter (>prior) threads', ())
where
threads' = toList threads
-- | A round-robin scheduler which doesn't pre-empt the running
-- thread.
roundRobinSchedNP :: Scheduler ()
roundRobinSchedNP = makeNP roundRobinSched
-- | Turn a potentially pre-emptive scheduler into a non-preemptive
-- one.
makeNP :: Scheduler s -> Scheduler s
makeNP sched = newsched where
newsched s prior threads
| prior `elem` toList threads = (prior, s)
| otherwise = sched s prior threads