| Copyright | (c) The University of Glasgow 2003 |
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) |
| Maintainer | ffi@haskell.org |
| Stability | provisional |
| Portability | non-portable (requires concurrency) |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
Foreign.Concurrent
Description
FFI datatypes and operations that use or require concurrency (GHC only).
Synopsis
- newForeignPtr :: Ptr a -> IO () -> IO (ForeignPtr a)
- addForeignPtrFinalizer :: ForeignPtr a -> IO () -> IO ()
Concurrency-based ForeignPtr operations
These functions generalize their namesakes in the portable
Foreign.ForeignPtr module by allowing arbitrary IO actions
as finalizers. These finalizers necessarily run in a separate
thread, cf. Destructors, Finalizers and Synchronization,
by Hans Boehm, POPL, 2003.
newForeignPtr :: Ptr a -> IO () -> IO (ForeignPtr a) #
Turns a plain memory reference into a foreign object by
associating a finalizer - given by the monadic operation - with the
reference. The storage manager will start the finalizer, in a
separate thread, some time after the last reference to the
ForeignPtr is dropped. There is no guarantee of promptness, and
in fact there is no guarantee that the finalizer will eventually
run at all.
Note that references from a finalizer do not necessarily prevent
another object from being finalized. If A's finalizer refers to B
(perhaps using touchForeignPtr, then the only guarantee is that
B's finalizer will never be started before A's. If both A and B
are unreachable, then both finalizers will start together. See
touchForeignPtr for more on finalizer ordering.
addForeignPtrFinalizer :: ForeignPtr a -> IO () -> IO () #
This function adds a finalizer to the given ForeignPtr. The
finalizer will run before all other finalizers for the same
object which have already been registered.
This is a variant of Foreign.ForeignPtr.addForeignPtrFinalizer,
where the finalizer is an arbitrary IO action. When it is
invoked, the finalizer will run in a new thread.
NB. Be very careful with these finalizers. One common trap is that
if a finalizer references another finalized value, it does not
prevent that value from being finalized. In particular, Handles
are finalized objects, so a finalizer should not refer to a Handle
(including stdout, stdin or stderr).