1 -----------------------------------------------------------------------------
3 -- Module : Control.Concurrent.QSemN
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/core/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable
11 -- $Id: QSemN.hs,v 1.2 2002/04/24 16:31:37 simonmar Exp $
13 -- Quantity semaphores
15 -----------------------------------------------------------------------------
17 module Control.Concurrent.QSemN
19 newQSemN, -- :: Int -> IO QSemN
20 waitQSemN, -- :: QSemN -> Int -> IO ()
21 signalQSemN -- :: QSemN -> Int -> IO ()
26 import Control.Concurrent.MVar
28 newtype QSemN = QSemN (MVar (Int,[(Int,MVar ())]))
30 newQSemN :: Int -> IO QSemN
32 sem <- newMVar (init,[])
35 waitQSemN :: QSemN -> Int -> IO ()
36 waitQSemN (QSemN sem) sz = do
37 (avail,blocked) <- takeMVar sem -- gain ex. access
38 if (avail - sz) >= 0 then
39 -- discharging 'sz' still leaves the semaphore
40 -- in an 'unblocked' state.
41 putMVar sem (avail-sz,[])
44 putMVar sem (avail, blocked++[(sz,block)])
47 signalQSemN :: QSemN -> Int -> IO ()
48 signalQSemN (QSemN sem) n = do
49 (avail,blocked) <- takeMVar sem
50 (avail',blocked') <- free (avail+n) blocked
51 putMVar sem (avail',blocked')
53 free avail [] = return (avail,[])
54 free avail ((req,block):blocked)
57 free (avail-req) blocked
59 (avail',blocked') <- free avail blocked
60 return (avail',(req,block):blocked')