[J3] [EXTERNAL] Re: Custom Memory Allocator

Steidel, Jon L jon.l.steidel at intel.com
Mon Nov 18 13:35:02 EST 2019

Hi Reuben,

In the 5.0 spec on page 158 in section 2.11.13 allocate Directive at lines 1-2 is a Fortran restriction

  List items specified in the allocate directive must not have the ALLOCATABLE attribute unless the directive is associated with an allocate statement.

So, I think if the allocate directive appears immediately before an ALLOCATE statement, list items may be allocatable.  So, I think the following is 

  real, allocatable :: x(:), y(:)
  ! declare and initialize omp_allocator and omp_alloctraits

  !$omp allocate (x, y) allocator (xy_alloc)
  allocate (x(n), y(n))

In this case the allocate statement would use the allocator specified by xy_alloc.  A complete example can be found starting on page 342 of the OpenMP 5.0 
Examples document that is now available at http://www.openmp.org/specifications. 



-----Original Message-----
From: J3 <j3-bounces at mailman.j3-fortran.org> On Behalf Of Reuben D. Budiardja via J3
Sent: Friday, November 15, 2019 7:31 PM
To: Steidel, Jon L via J3 <j3 at mailman.j3-fortran.org>
Cc: Reuben D. Budiardja <reubendb at ornl.gov>
Subject: Re: [J3] [EXTERNAL] Re: Custom Memory Allocator

Hi Jon,

Interesting. I was not aware of this (but then again I am not yet fully familiar with OpenMP 5). However, in the spec it says for Fortran the list item "must not have the ALLOCATABLE attribute" unless associated with "allocate statement".

So I am not sure how this would solve my issue (provided I could find such compiler). Or am I misunderstanding thing?


On 11/15/2019 05:18 PM, Steidel, Jon L via J3 wrote:
> OpenMP 5.0 has the ALLOCATE directive, with the ALLOCATOR clause.  I don't know if you have access to an OpenMP 5.0 compiler (or if there is yet one available), or if this would work for you if you can find such a compiler.
> -jon
> -----Original Message-----
> From: J3 <j3-bounces at mailman.j3-fortran.org> On Behalf Of Reuben D. 
> Budiardja via J3
> Sent: Friday, November 15, 2019 2:30 PM
> To: j3 at mailman.j3-fortran.org
> Cc: Reuben D. Budiardja <reubendb at ornl.gov>
> Subject: [J3] Custom Memory Allocator
> 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

Reuben D. Budiardja
reubendb at ornl.gov | (865) 576-9519
National Center for Computational Sciences Oak Ridge National Laboratory

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