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{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE FlexibleContexts #-}
module Data.CyclicBuffer {- TODO: export list -} where
import Control.Concurrent.STM
import Control.Monad
import Data.Word
import Data.Array.MArray
import Data.Maybe
data CyclicBuffer a = CyclicBuffer
{ vwflgs :: TArray Word32 Bool -- TODO: Use TVar. TArray Word32 (TVar Bool)
-- This would allow updating by external code.
-- The TVar could be returned from dequeue
, pktq :: TArray Word32 (Maybe a)
, seqno :: TVar Word32
, qsize :: Word32
, buffend :: TVar Word32 -- on incoming, highest packet number handled + 1
, dropCnt :: TVar Word32
, totalCnt :: TVar Word32
}
cyclicBufferViewList :: CyclicBuffer a -> STM [(Word32,a)]
cyclicBufferViewList p = do
let f (n,Nothing) = Nothing
f (n,Just x) = Just (n,x)
catMaybes . map f <$> getAssocs (pktq p)
getCapacity :: Applicative m => CyclicBuffer t -> m Word32
getCapacity (CyclicBuffer { qsize }) = pure qsize
getTotal :: CyclicBuffer t -> STM Word32
getTotal (CyclicBuffer { totalCnt }) = readTVar totalCnt
getDropped :: CyclicBuffer t -> STM Word32
getDropped (CyclicBuffer { dropCnt }) = readTVar dropCnt
getNextSequenceNum :: CyclicBuffer t -> STM Word32
getNextSequenceNum (CyclicBuffer { seqno }) = readTVar seqno
-- | Create a new CyclicBuffer with Overwrite on Wrap.
new :: Word32 -- ^ Capacity of queue.
-> Word32 -- ^ Initial sequence number.
-> STM (CyclicBuffer a)
new capacity seqstart = do
let cap = if capacity `mod` 2 == 0 then capacity else capacity + 1
q <- newArray (0,cap - 1) Nothing
flgs <- newArray (0,cap - 1) False
seqv <- newTVar seqstart
bufe <- newTVar 0
dropped <- newTVar 0
total <- newTVar 0
return CyclicBuffer
{ vwflgs = flgs
, pktq = q
, seqno = seqv
, qsize = cap
, buffend = bufe
, dropCnt = dropped
, totalCnt = total
}
observeOutOfBand :: CyclicBuffer a -> Word32-> STM ()
observeOutOfBand CyclicBuffer { seqno, qsize, buffend } no = do
low <- readTVar seqno
let proj = no - low
-- Ignore packet if out of range.
when ( proj < qsize) $ do
modifyTVar' buffend (\be -> if be - low <= proj then no + 1 else be)
-- | Retry until the next expected packet is enqueued. Then return it.
dequeue :: CyclicBuffer a -> STM a
dequeue CyclicBuffer { pktq, seqno, qsize } = do
i0 <- readTVar seqno
let i = i0 `mod` qsize
x <- maybe retry return =<< readArray pktq i
writeArray pktq i Nothing
modifyTVar' seqno succ
return x
-- | Like dequeue, but just marks as viewed rather than removing
markButNotDequeue :: CyclicBuffer a -> STM a
markButNotDequeue CyclicBuffer { vwflgs, pktq, seqno, qsize } = do
i0 <- readTVar seqno
let i = i0 `mod` qsize
x <- maybe retry return =<< readArray pktq i
writeArray vwflgs i True
modifyTVar' seqno succ
return x
-- | Enqueue a packet. If the capacity is exceeded, packets are
-- dropped and the drop count increased accordingly.
-- TODO: We no longer really support "out of order"
-- So perhaps drop the num parameter
enqueue :: CyclicBuffer a -- ^ The cyclic buffer(queue)
-> Word32 -- ^ Sequence number of the packet.
-> a -- ^ The packet.
-> STM ()
enqueue CyclicBuffer{vwflgs, pktq, seqno, qsize, buffend, dropCnt, totalCnt} no x = do
low <- readTVar seqno
let proj = no - low
let i = no `mod` qsize
when (proj >= qsize) $ do
viewed <- readArray vwflgs i
when (not viewed) $
modifyTVar' dropCnt (+1)
writeArray pktq i (Just x)
writeArray vwflgs i False -- mark as not viewed
modifyTVar' totalCnt (+1)
writeTVar seqno (no+1)
modifyTVar' buffend (\be -> if be - low <= proj then no + 1 else be)
return ()
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