{-# LANGUAGE CPP #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE NamedFieldPuns #-}
module CRDT.LamportClock
( Pid (..)
, Clock (..)
, LamportTime (..)
, getTime
, LocalTime
, Process (..)
, LamportClock
, runLamportClock
, getRealLocalTime
, getMacAddress
) 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 (StateT)
import Control.Monad.Trans (lift)
import Data.Time.Clock.POSIX (getPOSIXTime)
import Data.Word (Word64)
import Numeric.Natural (Natural)
import MacAddress (getMacAddress)
type LocalTime = Natural
data LamportTime = LamportTime LocalTime Pid
deriving (Eq, Ord)
instance Show LamportTime where
show (LamportTime time (Pid pid)) = show time ++ '.' : show pid
newtype Pid = Pid Word64
deriving (Eq, Ord, Show)
class Monad m => Process m where
getPid :: m Pid
getRealLocalTime :: IO LocalTime
getRealLocalTime = round . (* 10000000) <$> getPOSIXTime
class Process m => Clock m where
getTimes
:: Natural
-> m LamportTime
advance :: LocalTime -> m ()
getTime :: Clock m => m LamportTime
getTime = getTimes 1
newtype LamportClock a = LamportClock (ReaderT (TVar LocalTime) IO a)
deriving (Applicative, Functor, Monad, MonadIO)
runLamportClock :: TVar LocalTime -> LamportClock a -> IO a
runLamportClock var (LamportClock action) = runReaderT action var
instance Process LamportClock where
getPid = Pid <$> liftIO getMacAddress
instance Clock LamportClock where
advance time = LamportClock $ do
timeVar <- ask
lift $ atomically $ modifyTVar' timeVar $ max time
getTimes n' = LamportTime <$> getTimes' <*> getPid
where
n = max n' 1
getTimes' = LamportClock $ do
timeVar <- ask
lift $ do
realTime <- getRealLocalTime
atomically $ do
timeCur <- readTVar timeVar
let timeRangeStart = max realTime (timeCur + 1)
writeTVar timeVar $ timeRangeStart + n - 1
pure timeRangeStart
instance Process m => Process (ReaderT r m) where
getPid = lift getPid
instance Process m => Process (StateT s m) where
getPid = lift getPid
instance Clock m => Clock (ReaderT r m) where
advance = lift . advance
getTimes = lift . getTimes
instance Clock m => Clock (StateT s m) where
advance = lift . advance
getTimes = lift . getTimes