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63 lines
2.1 KiB
Haskell
63 lines
2.1 KiB
Haskell
-- | This is almost Control.Concurrent.Classy.QSemN, but it also has a function to snapshot the remaining quantity.
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module QSemN where
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import Control.Concurrent.Classy.MVar
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import Control.Monad.Catch (mask_, onException,
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uninterruptibleMask_)
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import Control.Monad.Conc.Class (MonadConc)
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import Data.Maybe
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newtype QSemN m = QSemN (MVar m (Int, [(Int, MVar m ())], [(Int, MVar m ())]))
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newQSemN :: MonadConc m => Int -> m (QSemN m)
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newQSemN initial
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| initial < 0 = fail "newQSemN: Initial quantity must be non-negative"
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| otherwise = QSemN <$> newMVar (initial, [], [])
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remainingQSemN :: MonadConc m => QSemN m -> m Int
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remainingQSemN (QSemN m) = (\(quantity, _, _) -> quantity) <$> readMVar m
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waitQSemN :: MonadConc m => QSemN m -> Int -> m ()
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waitQSemN (QSemN m) sz = mask_ $ do
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(quantity, b1, b2) <- takeMVar m
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let remaining = quantity - sz
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if remaining < 0
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then do
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b <- newEmptyMVar
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putMVar m (quantity, b1, (sz,b):b2)
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wait b
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else
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putMVar m (remaining, b1, b2)
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where
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wait b = takeMVar b `onException` uninterruptibleMask_ (do
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(quantity, b1, b2) <- takeMVar m
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r <- tryTakeMVar b
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r' <- if isJust r
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then signal sz (quantity, b1, b2)
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else putMVar b () >> pure (quantity, b1, b2)
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putMVar m r')
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signalQSemN :: MonadConc m => QSemN m -> Int -> m ()
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signalQSemN (QSemN m) sz = uninterruptibleMask_ $ do
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r <- takeMVar m
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r' <- signal sz r
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putMVar m r'
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signal :: MonadConc m
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=> Int
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-> (Int, [(Int,MVar m ())], [(Int,MVar m ())])
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-> m (Int, [(Int,MVar m ())], [(Int,MVar m ())])
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signal sz0 (i,a1,a2) = loop (sz0 + i) a1 a2 where
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loop 0 bs b2 = pure (0, bs, b2)
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loop sz [] [] = pure (sz, [], [])
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loop sz [] b2 = loop sz (reverse b2) []
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loop sz ((j,b):bs) b2
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| j > sz = do
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r <- isEmptyMVar b
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if r then pure (sz, (j,b):bs, b2)
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else loop sz bs b2
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| otherwise = do
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r <- tryPutMVar b ()
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if r then loop (sz-j) bs b2
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else loop sz bs b2
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