1 -----------------------------------------------------------------------------
3 -- Module : Control.Concurrent.QSemN
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable (concurrency)
11 -- Quantity semaphores in which each thread may wait for an arbitrary
14 -----------------------------------------------------------------------------
16 module Control.Concurrent.QSemN
17 ( -- * General Quantity Semaphores
19 newQSemN, -- :: Int -> IO QSemN
20 waitQSemN, -- :: QSemN -> Int -> IO ()
21 signalQSemN -- :: QSemN -> Int -> IO ()
26 import Control.Concurrent.MVar
28 -- |A 'QSemN' is a quantity semaphore, in which the available
29 -- \"quantity\" may be signalled or waited for in arbitrary amounts.
30 newtype QSemN = QSemN (MVar (Int,[(Int,MVar ())]))
32 -- |Build a new 'QSemN' with a supplied initial quantity.
33 newQSemN :: Int -> IO QSemN
35 sem <- newMVar (init,[])
38 -- |Wait for the specified quantity to become available
39 waitQSemN :: QSemN -> Int -> IO ()
40 waitQSemN (QSemN sem) sz = do
41 (avail,blocked) <- takeMVar sem -- gain ex. access
42 if (avail - sz) >= 0 then
43 -- discharging 'sz' still leaves the semaphore
44 -- in an 'unblocked' state.
45 putMVar sem (avail-sz,blocked)
48 putMVar sem (avail, blocked++[(sz,block)])
51 -- |Signal that a given quantity is now available from the 'QSemN'.
52 signalQSemN :: QSemN -> Int -> IO ()
53 signalQSemN (QSemN sem) n = do
54 (avail,blocked) <- takeMVar sem
55 (avail',blocked') <- free (avail+n) blocked
56 putMVar sem (avail',blocked')
58 free avail [] = return (avail,[])
59 free avail ((req,block):blocked)
62 free (avail-req) blocked
64 (avail',blocked') <- free avail blocked
65 return (avail',(req,block):blocked')