1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
4 -- Module : GHC.ForeignPtr
5 -- Copyright : (c) The University of Glasgow, 1992-2003
6 -- License : see libraries/base/LICENSE
8 -- Maintainer : cvs-ghc@haskell.org
9 -- Stability : internal
10 -- Portability : non-portable (GHC extensions)
12 -- GHC's implementation of the 'ForeignPtr' data type.
14 -----------------------------------------------------------------------------
23 mallocForeignPtrBytes,
24 addForeignPtrFinalizer,
26 unsafeForeignPtrToPtr,
29 addForeignPtrConcFinalizer,
32 import Control.Monad ( sequence_ )
34 import Foreign.Storable
37 import GHC.List ( null )
40 import GHC.Ptr ( Ptr(..) )
44 -- |The type 'ForeignPtr' represents references to objects that are
45 -- maintained in a foreign language, i.e., that are not part of the
46 -- data structures usually managed by the Haskell storage manager.
47 -- The essential difference between 'ForeignPtr's and vanilla memory
48 -- references of type @Ptr a@ is that the former may be associated
49 -- with /finalisers/. A finaliser is a routine that is invoked when
50 -- the Haskell storage manager detects that - within the Haskell heap
51 -- and stack - there are no more references left that are pointing to
52 -- the 'ForeignPtr'. Typically, the finaliser will, then, invoke
53 -- routines in the foreign language that free the resources bound by
54 -- the foreign object.
56 -- The 'ForeignPtr' is parameterised in the same way as 'Ptr'. The
57 -- type argument of 'ForeignPtr' should normally be an instance of
61 = ForeignPtr ForeignObj# !(IORef [IO ()])
62 | MallocPtr (MutableByteArray# RealWorld) !(IORef [IO ()])
64 instance Eq (ForeignPtr a) where
65 p == q = unsafeForeignPtrToPtr p == unsafeForeignPtrToPtr q
67 instance Ord (ForeignPtr a) where
68 compare p q = compare (unsafeForeignPtrToPtr p) (unsafeForeignPtrToPtr q)
70 instance Show (ForeignPtr a) where
71 showsPrec p f = showsPrec p (unsafeForeignPtrToPtr f)
74 INSTANCE_TYPEABLE1(ForeignPtr,foreignPtrTc,"ForeignPtr")
76 -- |A Finaliser is represented as a pointer to a foreign function that, at
77 -- finalisation time, gets as an argument a plain pointer variant of the
78 -- foreign pointer that the finalizer is associated with.
80 type FinalizerPtr a = FunPtr (Ptr a -> IO ())
82 newForeignPtr :: Ptr a -> FinalizerPtr a -> IO (ForeignPtr a)
83 -- ^Turns a plain memory reference into a foreign pointer, and
84 -- associates a finaliser with the reference. The finaliser will be executed
85 -- after the last reference to the foreign object is dropped. Note that there
86 -- is no guarantee on how soon the finaliser is executed after the last
87 -- reference was dropped; this depends on the details of the Haskell storage
88 -- manager. The only guarantee is that the finaliser runs before the program
90 newForeignPtr p finalizer
91 = do fObj <- newForeignPtr_ p
92 addForeignPtrFinalizer fObj finalizer
95 newConcForeignPtr :: Ptr a -> IO () -> IO (ForeignPtr a)
96 -- ^Turns a plain memory reference into a foreign object
97 -- by associating a finaliser - given by the monadic operation
98 -- - with the reference. The finaliser will be executed after
99 -- the last reference to the foreign object is dropped. Note
100 -- that there is no guarantee on how soon the finaliser is
101 -- executed after the last reference was dropped; this depends
102 -- on the details of the Haskell storage manager. The only
103 -- guarantee is that the finaliser runs before the program
106 -- The finalizer, when invoked, will run in a separate thread.
108 newConcForeignPtr p finalizer
109 = do fObj <- newForeignPtr_ p
110 addForeignPtrConcFinalizer fObj finalizer
113 mallocForeignPtr :: Storable a => IO (ForeignPtr a)
114 -- ^ allocates some memory and returns a ForeignPtr to it. The memory
115 -- will be released automatically when the ForeignPtr is discarded.
117 -- @mallocForeignPtr@ is equivalent to
119 -- > do { p <- malloc; newForeignPtr p free }
121 -- although it may be implemented differently internally. You may not
122 -- assume that the memory returned by 'mallocForeignPtr' has been
123 -- allocated with C's @malloc()@.
124 mallocForeignPtr = doMalloc undefined
125 where doMalloc :: Storable a => a -> IO (ForeignPtr a)
129 case newPinnedByteArray# size s of { (# s, mbarr# #) ->
130 (# s, MallocPtr mbarr# r #)
132 where (I# size) = sizeOf a
134 -- | similar to 'mallocForeignPtr', except that the size of the memory required
135 -- is given explicitly as a number of bytes.
136 mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
137 mallocForeignPtrBytes (I# size) = do
140 case newPinnedByteArray# size s of { (# s, mbarr# #) ->
141 (# s, MallocPtr mbarr# r #)
144 addForeignPtrFinalizer :: ForeignPtr a -> FinalizerPtr a -> IO ()
145 -- ^This function adds a finaliser to the given foreign object. The
146 -- finalizer will run /before/ all other finalizers for the same
147 -- object which have already been registered.
148 addForeignPtrFinalizer fptr finalizer =
149 addForeignPtrConcFinalizer fptr
150 (mkFinalizer finalizer (unsafeForeignPtrToPtr fptr))
152 addForeignPtrConcFinalizer :: ForeignPtr a -> IO () -> IO ()
153 -- ^This function adds a finaliser to the given @ForeignPtr@. The
154 -- finalizer will run /before/ all other finalizers for the same
155 -- object which have already been registered.
157 -- This is a variant of @addForeignPtrFinalizer@, where the finalizer
158 -- is an arbitrary @IO@ action. When it is invoked, the finalizer
159 -- will run in a new thread.
161 addForeignPtrConcFinalizer f@(ForeignPtr fo r) finalizer = do
163 writeIORef r (finalizer : fs)
166 let p = unsafeForeignPtrToPtr f in
167 case mkWeak# fo () (foreignPtrFinalizer r p) s of
168 (# s1, w #) -> (# s1, () #)
170 addForeignPtrConcFinalizer f@(MallocPtr fo r) finalizer = do
172 writeIORef r (finalizer : fs)
175 let p = unsafeForeignPtrToPtr f in
176 case mkWeak# fo () (foreignPtrFinalizer r p) s of
177 (# s1, w #) -> (# s1, () #)
180 foreign import ccall "dynamic"
181 mkFinalizer :: FinalizerPtr a -> Ptr a -> IO ()
183 foreignPtrFinalizer :: IORef [IO ()] -> Ptr a -> IO ()
184 foreignPtrFinalizer r p = do
188 newForeignPtr_ :: Ptr a -> IO (ForeignPtr a)
189 -- ^Turns a plain memory reference into a foreign pointer that may be
190 -- associated with finalizers by using 'addForeignPtrFinalizer'.
191 newForeignPtr_ (Ptr obj) = do
194 case mkForeignObj# obj s# of
195 (# s1#, fo# #) -> (# s1#, ForeignPtr fo# r #)
197 touchForeignPtr :: ForeignPtr a -> IO ()
198 -- ^This function ensures that the foreign object in
199 -- question is alive at the given place in the sequence of IO
200 -- actions. In particular 'withForeignPtr'
201 -- does a 'touchForeignPtr' after it
202 -- executes the user action.
204 -- This function can be used to express liveness
205 -- dependencies between 'ForeignPtr's: for
206 -- example, if the finalizer for one
207 -- 'ForeignPtr' touches a second
208 -- 'ForeignPtr', then it is ensured that the
209 -- second 'ForeignPtr' will stay alive at
210 -- least as long as the first. This can be useful when you
211 -- want to manipulate /interior pointers/ to
212 -- a foreign structure: you can use
213 -- 'touchForeignObj' to express the
214 -- requirement that the exterior pointer must not be finalized
215 -- until the interior pointer is no longer referenced.
216 touchForeignPtr (ForeignPtr fo r)
217 = IO $ \s -> case touch# fo s of s -> (# s, () #)
218 touchForeignPtr (MallocPtr fo r)
219 = IO $ \s -> case touch# fo s of s -> (# s, () #)
221 unsafeForeignPtrToPtr :: ForeignPtr a -> Ptr a
222 -- ^This function extracts the pointer component of a foreign
223 -- pointer. This is a potentially dangerous operations, as if the
224 -- argument to 'unsafeForeignPtrToPtr' is the last usage
225 -- occurence of the given foreign pointer, then its finaliser(s) will
226 -- be run, which potentially invalidates the plain pointer just
227 -- obtained. Hence, 'touchForeignPtr' must be used
228 -- wherever it has to be guaranteed that the pointer lives on - i.e.,
229 -- has another usage occurrence.
231 -- To avoid subtle coding errors, hand written marshalling code
232 -- should preferably use 'withForeignPtr' rather
233 -- than combinations of 'unsafeForeignPtrToPtr' and
234 -- 'touchForeignPtr'. However, the later routines
235 -- are occasionally preferred in tool generated marshalling code.
236 unsafeForeignPtrToPtr (ForeignPtr fo r) = Ptr (foreignObjToAddr# fo)
237 unsafeForeignPtrToPtr (MallocPtr fo r) = Ptr (byteArrayContents# (unsafeCoerce# fo))
239 castForeignPtr :: ForeignPtr a -> ForeignPtr b
240 -- ^This function casts a 'ForeignPtr'
241 -- parameterised by one type into another type.
242 castForeignPtr f = unsafeCoerce# f