Hi Damian, hi Steve,
enabling coarray-support by default has implications we need to consider. The
memory footprint of a coarray enabled program is larger than the one of a
non-coarray one. This is simply because the coarray token needs to be stored
somewhere.
Furthermore, I just yesterday figured, that with -fcoarray=single the space for
the token was allocated. I.e. every data structure, that could possibly be
stored in a coarray and had allocatable components in it, wasted another 8 byte
for an unused pointer.
So when we default to having coarray support enabled, some work needs to be
done, to remove such inefficiencies. Given there are only a few developers,
that work on coarrays, this may take some time.
What we can of course do, is to switch on the coarray mode, when we detect the
first coarray construct and no longer need the user to do it. I hope this does
not have to many implications and causes only a hand full of bugs.
For the time being, I propose to first give the new coarray implementation some
time to mature and test. There will be bugs, because nobody is perfect.
@Steve caf_shmem does not use MPI. It is a shared memory, single node, multi
process approach. Just to prevent any misunderstanding.
Thanks for all the testing.
Regards,
Andre
On Tue, 24 Jun 2025 11:13:52 -0700
Steve Kargl <s...@troutmask.apl.washington.edu> wrote:
> Damian,
>
> I submitted a patch a long time ago to make -fcoarray=single the
> default behavior. The patch made -fcoarray=none a NOP. With
> inclusion of a shmem implementation of the runtime parts, this
> might be the way to go. I'll leave that decision to Andre, Thomas,
> and Nicolas.
>
> I believe that the gfortran contributors have not considered
> coarray as an optional add-on. The problem for gfortran is
> that it runs on dozens of CPUs and dozens upon dozens of
> operating systems. The few gfortran contributors simply cannot
> ensure that opencoarray+mpich or opencoarray+openmpi runs on
> all of the possible combinations of hardware and OS's. Andre
> has hinted that he expects some rough edges on non-linux system.
> I'll find out this weekend when I give his patch a spin on
> FreeBSD. Hopefully, a windows10/11 user can test the patch.
>
--
Andre Vehreschild * Email: vehre ad gmx dot de
