4d75b31446f6d00ab375508db7d11bc8971b83e8
[packages/base.git] / System / Mem / Weak.hs
1 -----------------------------------------------------------------------------
2 -- |
3 -- Module : System.Mem.Weak
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/core/LICENSE)
6 --
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable
10 --
11 -- Weak references, weak pairs, weak pointers, and finalizers.
12 --
13 -----------------------------------------------------------------------------
14
15 module System.Mem.Weak (
16 Weak, -- abstract
17 -- instance Eq (Weak v)
18
19 mkWeak, -- :: k -> v -> Maybe (IO ()) -> IO (Weak v)
20 deRefWeak, -- :: Weak v -> IO (Maybe v)
21 finalize, -- :: Weak v -> IO ()
22 -- replaceFinaliser -- :: Weak v -> IO () -> IO ()
23
24 mkWeakPtr, -- :: k -> Maybe (IO ()) -> IO (Weak k)
25 mkWeakPair, -- :: k -> v -> Maybe (IO ()) -> IO (Weak (k,v))
26 addFinalizer -- :: key -> IO () -> IO ()
27 ) where
28
29 import Prelude
30
31 import Data.Dynamic
32
33 #ifdef __GLASGOW_HASKELL__
34 import GHC.Base
35 import GHC.IOBase
36 import GHC.Weak
37
38 #include "Dynamic.h"
39 INSTANCE_TYPEABLE1(Weak,weakTc,"Weak")
40
41 deRefWeak :: Weak v -> IO (Maybe v)
42 deRefWeak (Weak w) = IO $ \s ->
43 case deRefWeak# w s of
44 (# s1, flag, p #) -> case flag of
45 0# -> (# s1, Nothing #)
46 _ -> (# s1, Just p #)
47
48 mkWeakPair :: k -> v -> Maybe (IO ()) -> IO (Weak (k,v))
49 mkWeakPair key val finalizer = mkWeak key (key,val) finalizer
50
51 finalize :: Weak v -> IO ()
52 finalize (Weak w) = IO $ \s ->
53 case finalizeWeak# w s of
54 (# s1, 0#, _ #) -> (# s1, () #) -- already dead, or no finaliser
55 (# s1, _, f #) -> f s1
56 #endif
57