--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable
+-- Portability : non-portable (concurrency)
--
--- Quantity semaphores
+-- Quantity semaphores in which each thread may wait for an arbitrary
+-- \"amount\".
--
-----------------------------------------------------------------------------
module Control.Concurrent.QSemN
- ( QSemN, -- abstract
+ ( -- * General Quantity Semaphores
+ QSemN, -- abstract
newQSemN, -- :: Int -> IO QSemN
waitQSemN, -- :: QSemN -> Int -> IO ()
signalQSemN -- :: QSemN -> Int -> IO ()
import Control.Concurrent.MVar
+-- |A 'QSemN' is a quantity semaphore, in which the available
+-- \"quantity\" may be signalled or waited for in arbitrary amounts.
newtype QSemN = QSemN (MVar (Int,[(Int,MVar ())]))
+-- |Build a new 'QSemN' with a supplied initial quantity.
newQSemN :: Int -> IO QSemN
newQSemN init = do
sem <- newMVar (init,[])
return (QSemN sem)
+-- |Wait for the specified quantity to become available
waitQSemN :: QSemN -> Int -> IO ()
waitQSemN (QSemN sem) sz = do
(avail,blocked) <- takeMVar sem -- gain ex. access
putMVar sem (avail, blocked++[(sz,block)])
takeMVar block
+-- |Signal that a given quantity is now available from the 'QSemN'.
signalQSemN :: QSemN -> Int -> IO ()
signalQSemN (QSemN sem) n = do
(avail,blocked) <- takeMVar sem