Finalizers finalized

[Manuel M T Chakravarty]

Ross Paterson <ross at soi.city.ac.uk> wrote,

> On Fri, Jan 17, 2003 at 10:23:27AM +1100, Manuel M T Chakravarty wrote:
> > Ross Paterson <ross at soi.city.ac.uk> wrote,
> > 
> > > I'd also like to see the addition of
> > > 
> > > 	mallocForeignPtrArray :: Storable a => Int -> IO (ForeignPtr a)
> > > 
> > > to ForeignPtr, to save people from rolling their own.  (Maybe the realloc
> > > and 0 versions too?)
> > 
> > The reason I didn't answer to this earlier is that I wanted
> > to see how many people say that they support this addition.
> > To be honest, I never needed a function like this.  Did
> > anybody else?
> 
> Only me, it seems.  But surely if both mallocForeignPtr and mallocArray
> are useful, this is too.
>
> If you don't want to do explicit deallocation, mallocForeignPtr is
> attractive (and handled specially by GHC).  Sooner or later there are
> going to be arrays, and then if there's no such function you'll have to
> write your own.

Yes, I think you are right that an orthogonality argument
can be made here.  So, let's add the function.  I assume
from the silence on this topic that nobody has an serious
objections to adding this function.
`mallocForeignPtrArray0' should then also be added, as you
say.

I am not so sure about a realloc version.  It, at least,
requires some care, as realloc may return a pointer different
from the original.  (In other words, there is no guarantee
that realloc works in-place.)  I just noticed that the spec
doesn't mention this; so, I'll add it.  We should also
include the special cases that the C library covers:

* If `realloc' is passed a `nullPtr', it works like
  `malloc'.

* If the size requested from `reallocBytes' is 0, it works
  like `free'.

Finally, I am not sure whether we really want to allow that
`reallocBytes' may be used on `alloca'ed memory, which the
spec currently explicitly admits.


Proposed changes
~~~~~~~~~~~~~~~~

Add to `ForeignPtr':

  mallocForeignPtrArray  :: Storable a => Int -> IO (ForeignPtr a)
  mallocForeignPtrArray0 :: Storable a => Int -> IO (ForeignPtr a)

Refine spec of `MarshalAlloc' as follows:

* realloc may return a pointer other than the one passed in.
  State special cases for passing `nullPtr' and size of 0,
  respectively, to `realloc' as stated above.

[I will already apply these changes.]


Open questions (feedback requested)
~~~~~~~~~~~~~~

* Shall we remove the sentence allowing `reallocBytes' on
  `alloca'ed memory?

* Shall we provide reallocForeignPtrArray and
  reallocForeignPtrArray0? 

[I will not apply these changes until after further
discussion.] 

Cheers,
Manuel