Remove Control.Parallel*, now in package parallel
[packages/random.git] / Control / Concurrent / QSemN.hs
1 -----------------------------------------------------------------------------
2 -- |
3 -- Module : Control.Concurrent.QSemN
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
6 --
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable (concurrency)
10 --
11 -- Quantity semaphores in which each thread may wait for an arbitrary
12 -- \"amount\".
13 --
14 -----------------------------------------------------------------------------
15
16 module Control.Concurrent.QSemN
17 ( -- * General Quantity Semaphores
18 QSemN, -- abstract
19 newQSemN, -- :: Int -> IO QSemN
20 waitQSemN, -- :: QSemN -> Int -> IO ()
21 signalQSemN -- :: QSemN -> Int -> IO ()
22 ) where
23
24 import Prelude
25
26 import Control.Concurrent.MVar
27 import Data.Typeable
28
29 #include "Typeable.h"
30
31 -- |A 'QSemN' is a quantity semaphore, in which the available
32 -- \"quantity\" may be signalled or waited for in arbitrary amounts.
33 newtype QSemN = QSemN (MVar (Int,[(Int,MVar ())]))
34
35 INSTANCE_TYPEABLE0(QSemN,qSemNTc,"QSemN")
36
37 -- |Build a new 'QSemN' with a supplied initial quantity.
38 newQSemN :: Int -> IO QSemN
39 newQSemN init = do
40 sem <- newMVar (init,[])
41 return (QSemN sem)
42
43 -- |Wait for the specified quantity to become available
44 waitQSemN :: QSemN -> Int -> IO ()
45 waitQSemN (QSemN sem) sz = do
46 (avail,blocked) <- takeMVar sem -- gain ex. access
47 if (avail - sz) >= 0 then
48 -- discharging 'sz' still leaves the semaphore
49 -- in an 'unblocked' state.
50 putMVar sem (avail-sz,blocked)
51 else do
52 block <- newEmptyMVar
53 putMVar sem (avail, blocked++[(sz,block)])
54 takeMVar block
55
56 -- |Signal that a given quantity is now available from the 'QSemN'.
57 signalQSemN :: QSemN -> Int -> IO ()
58 signalQSemN (QSemN sem) n = do
59 (avail,blocked) <- takeMVar sem
60 (avail',blocked') <- free (avail+n) blocked
61 putMVar sem (avail',blocked')
62 where
63 free avail [] = return (avail,[])
64 free avail ((req,block):blocked)
65 | avail >= req = do
66 putMVar block ()
67 free (avail-req) blocked
68 | otherwise = do
69 (avail',blocked') <- free avail blocked
70 return (avail',(req,block):blocked')