module CRDT.LamportClock
( Pid (..)
, Clock (..)
, LamportTime (..)
, LocalTime
, Process (..)
, LamportClockSim (..)
, ProcessSim (..)
, runLamportClockSim
, runProcessSim
, LamportClock
, runLamportClock
, getRealLocalTime
) where
import Control.Concurrent.STM (TVar, atomically, modifyTVar',
readTVar, writeTVar)
import Control.Monad.IO.Class (MonadIO, liftIO)
import Control.Monad.Reader (ReaderT, ask, runReaderT)
import Control.Monad.State.Strict (State, evalState, modify, state)
import Control.Monad.Trans (lift)
import Data.Binary (decode)
import qualified Data.ByteString.Lazy as BSL
import Data.Map.Strict (Map)
import qualified Data.Map.Strict as Map
import Data.Maybe (fromMaybe)
import Data.Time.Clock.POSIX (getPOSIXTime)
import Data.Word (Word64)
import Network.Info (MAC (MAC), getNetworkInterfaces, mac)
import Numeric (showHex)
import Numeric.Natural (Natural)
import Safe (headDef)
type LocalTime = Natural
data LamportTime = LamportTime !LocalTime !Pid
deriving (Eq, Ord)
instance Show LamportTime where
show (LamportTime time (Pid pid)) = showHex time "" ++ '-' : showHex pid ""
newtype Pid = Pid Word64
deriving (Eq, Ord, Show)
newtype LamportClockSim a = LamportClockSim (State (Map Pid LocalTime) a)
deriving (Applicative, Functor, Monad)
newtype ProcessSim a = ProcessSim (ReaderT Pid LamportClockSim a)
deriving (Applicative, Functor, Monad)
class Monad m => Process m where
getPid :: m Pid
runLamportClockSim :: LamportClockSim a -> a
runLamportClockSim (LamportClockSim action) = evalState action mempty
runProcessSim :: Pid -> ProcessSim a -> LamportClockSim a
runProcessSim pid (ProcessSim action) = runReaderT action pid
preIncrementAt :: Pid -> LamportClockSim LocalTime
preIncrementAt pid =
LamportClockSim . state $ \m -> let
lt' = succ . fromMaybe 0 $ Map.lookup pid m
in (lt', Map.insert pid lt' m)
getRealLocalTime :: IO LocalTime
getRealLocalTime = round . (* 10000000) <$> getPOSIXTime
getPidByMac :: IO Pid
getPidByMac = Pid . decodeMac <$> getMac
where
getMac :: IO MAC
getMac =
headDef (error "Can't get any non-zero MAC address of this machine")
. filter (/= minBound)
. map mac
<$> getNetworkInterfaces
decodeMac :: MAC -> Word64
decodeMac (MAC b5 b4 b3 b2 b1 b0) =
decode $ BSL.pack [0, 0, b5, b4, b3, b2, b1, b0]
class Process m => Clock m where
getTime :: m LamportTime
advance :: LocalTime -> m ()
instance Process ProcessSim where
getPid = ProcessSim ask
instance Clock ProcessSim where
getTime = ProcessSim $ do
pid <- ask
time <- lift $ preIncrementAt pid
pure $ LamportTime time pid
advance time = ProcessSim $ do
pid <- ask
lift . LamportClockSim . modify $ Map.insertWith max pid time
newtype LamportClock a = LamportClock (ReaderT (TVar LocalTime) IO a)
deriving (Applicative, Functor, Monad, MonadIO)
runLamportClock :: TVar LocalTime -> LamportClock a -> IO a
runLamportClock var (LamportClock action) = runReaderT action var
instance Process LamportClock where
getPid = liftIO getPidByMac
instance Clock LamportClock where
advance time = LamportClock $ do
timeVar <- ask
lift $ atomically $ modifyTVar' timeVar $ max time
getTime = LamportClock $ do
timeVar <- ask
lift $ do
realTime <- getRealLocalTime
time1 <- atomically $ do
time0 <- readTVar timeVar
let time1 = max realTime (time0 + 1)
writeTVar timeVar time1
pure time1
pid <- getPidByMac
pure $ LamportTime time1 pid