#ifdef __GLASGOW_HASKELL__
#endif
module Control.Concurrent.QSemN
(
QSemN,
newQSemN,
waitQSemN,
signalQSemN
) where
import Prelude
import Control.Concurrent.MVar
import Control.Exception ( mask_ )
import Data.Typeable
#include "Typeable.h"
newtype QSemN = QSemN (MVar (Int,[(Int,MVar ())])) deriving Eq
INSTANCE_TYPEABLE0(QSemN,qSemNTc,"QSemN")
newQSemN :: Int -> IO QSemN
newQSemN initial =
if initial < 0
then fail "newQSemN: Initial quantity must be non-negative"
else do sem <- newMVar (initial, [])
return (QSemN sem)
waitQSemN :: QSemN -> Int -> IO ()
waitQSemN (QSemN sem) sz = mask_ $ do
(avail,blocked) <- takeMVar sem
let remaining = avail sz
if remaining >= 0 then
putMVar sem (remaining,blocked)
else do
b <- newEmptyMVar
putMVar sem (avail, blocked++[(sz,b)])
takeMVar b
signalQSemN :: QSemN -> Int -> IO ()
signalQSemN (QSemN sem) n = mask_ $ do
(avail,blocked) <- takeMVar sem
(avail',blocked') <- free (avail+n) blocked
avail' `seq` putMVar sem (avail',blocked')
where
free avail [] = return (avail,[])
free avail ((req,b):blocked)
| avail >= req = do
putMVar b ()
free (availreq) blocked
| otherwise = do
(avail',blocked') <- free avail blocked
return (avail',(req,b):blocked')
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