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 -- Quantity semaphores
13 -----------------------------------------------------------------------------
15 module Control.Concurrent.QSemN
17 newQSemN, -- :: Int -> IO QSemN
18 waitQSemN, -- :: QSemN -> Int -> IO ()
19 signalQSemN -- :: QSemN -> Int -> IO ()
24 import Control.Concurrent.MVar
26 newtype QSemN = QSemN (MVar (Int,[(Int,MVar ())]))
28 newQSemN :: Int -> IO QSemN
30 sem <- newMVar (init,[])
33 waitQSemN :: QSemN -> Int -> IO ()
34 waitQSemN (QSemN sem) sz = do
35 (avail,blocked) <- takeMVar sem -- gain ex. access
36 if (avail - sz) >= 0 then
37 -- discharging 'sz' still leaves the semaphore
38 -- in an 'unblocked' state.
39 putMVar sem (avail-sz,[])
42 putMVar sem (avail, blocked++[(sz,block)])
45 signalQSemN :: QSemN -> Int -> IO ()
46 signalQSemN (QSemN sem) n = do
47 (avail,blocked) <- takeMVar sem
48 (avail',blocked') <- free (avail+n) blocked
49 putMVar sem (avail',blocked')
51 free avail [] = return (avail,[])
52 free avail ((req,block):blocked)
55 free (avail-req) blocked
57 (avail',blocked') <- free avail blocked
58 return (avail',(req,block):blocked')