[J3] Custom Memory Allocator

[Steve Lionel]

No, there is no way to do this and if you try playing games with the
descriptor you may be in for big trouble later when the Fortran run-time
wants to deallocate the memory, as it isn't using the C descriptor for that.

My advice is that if you want to use a custom allocator, use POINTER and
CFI_establish (or C_F_POINTER on the Fortran side.) Admittedly you will be
giving up some of the advantages of allocatables.

Steve

On Fri, Nov 15, 2019 at 2:30 PM Reuben D. Budiardja via J3 <
j3 at mailman.j3-fortran.org> wrote:

> Hello,
>
> I am wondering if there is a standard-conformance way to allocate
> allocatable array with a custom memory allocator, e.g. via third-party
> provided C-library.
>
> At first I looked into passing the allocatable into a bind(c) subroutine
> and use the C descriptor from the C side. But sec 18.6 and 18.7 prevent
> using any custom allocator other than using CFI_allocate().
>
> Real-world use case examples: we need to use CUDA memory allocator
> cudaMallocManaged() to use CUDA Unified Memory, and cudaHostAlloc() to
> use page-locked memory on the system.
>
> I suppose the hack-ish way is to swap the base_address member of C
> descriptor to the address given cudaMallocManaged() (and free-up the
> original address from CFI_allocate()).
>
> I wondered if for further enhancement on C interoperability we may
> consider allowing custom allocator into the standard.
>
> I'd be interested in any feedback.
>
> Best,
> Reuben
>
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