Thanks Simon,
great stuff; I like the introduction of these 'native code finalizers',
they've
been sorely missed at times.
You don't say, but will there be a dynamic check to catch such re-entries?
--sigbjorn
On 1/14/2009 04:14, Simon Marlow wrote:
By popular demand, GHC 6.10.2 will support finalizers that are
actually guaranteed to run, and run promptly. There aren't any API
changes: this happens for finalizers created using newForeignPtr as
normal.
However, there's a catch. Previously it was possible to call back
into Haskell from a finalizer (finalizers are C functions), by using
foreign import "wrapper" or foreign export. According to the FFI
spec, whether this is allowed or not is "system dependent". In GHC
6.10.1 and earlier it was allowed, but in 6.10.2 and later it is not.
The reason being that C finalizers are now executed directly by the
GC, when the runtime is not in a position to handle callbacks.
You can still have fully-fledged Haskell finalizers if you want: we
have Foreign.Concurrent.newForeignPtr for that purpose. But those
finalizers are not subject to the same promptness guarantees that you
get with C finalizers - they run in a separate thread, and are not
guaranteed to be run at program exit.
We'll make sure this is documented prominently in the 6.10.2 release
notes, but I thought a heads-up would be a good idea right now as it
turns out that there are existing libraries (e.g. LLVM) that will be
affected.
Cheers,
Simon
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