-----------------------------------------------------------------------------
---
+-- |
-- Module : Control.Concurrent.QSemN
-- Copyright : (c) The University of Glasgow 2001
--- License : BSD-style (see the file libraries/core/LICENSE)
+-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable
---
--- $Id: QSemN.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
+-- 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 Prelude
import Control.Concurrent.MVar
+import Data.Typeable
+#include "Typeable.h"
+
+-- |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 ())]))
+INSTANCE_TYPEABLE0(QSemN,qSemNTc,"QSemN")
+
+-- |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
if (avail - sz) >= 0 then
-- discharging 'sz' still leaves the semaphore
-- in an 'unblocked' state.
- putMVar sem (avail-sz,[])
+ putMVar sem (avail-sz,blocked)
else do
block <- newEmptyMVar
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