Hi Gerald,
Gerald Pfeifer wrote:
On Sun, 31 Aug 2014, Tobias Burnus wrote:
I have committed the attached patch. Comment and suggestions are welcome!
I applied the small follow-up below.
What I am struggling to understand, though, is the following piece:
Full experimental support of Fortran 2008's coarrays with
<code>-fcoarray=lib</code> except for locking and allocatable/pointer
components of derived-type coarrays.
Does this mean it is only supported when -fcoarray=lib is provided?
If so, I'd say that more explicitly.
No, not quite. Let' me expand a bit: Coarrays permit to run programs in
parallel following a distributed memory model. All variables which are
coarrays have an additional (array) index designating the (remote)
processor index ("image index"). gfortran handles this parallelization
by generating calls to a communication library (libcaf_single,
libcaf_mpi, libcaf_armci, ...). (The option -fcoarray=single assumes
that only a single process exists [boring!] and requires no
communication library.)
As just written, with -fcoarray=lib, one generates library calls for the
communication with remote processes ("images"). However, the
implementation is not yet complete. And the biggest omission is the
support to access allocatable or pointer components of coarrays. Namely,
either to pull data from a remote image/process in the form:
lhs = coarray[remote_index]%allocatable_component
or to push data to a remote image, e.g.
coarray[remote_index]%pointer_component = 5
As that's the main missing feature, I thought it should be listed in the
release notes.
When accessing data for the local process, it uses the normal code and,
hence, it automatically works with -fcoarray=single. Trying to access
code from a remote process will give a compile-time error with a
sorry-not-yet-implemented error.
And perhaps split off the second half into something like "(Only
locking and... are not provided yet)".
Locking is meanwhile supported (except for a corner case).
What is "full experimental support", by the way? Just "experimental"?
Well, except for some corner cases – and in particular the the listed
one – all features are supported. Thus, there is full support of
coarrays as defined in Fortran 2008. But it is only experimental as
there are known and unknown bugs.
I hope, it is now clearer what was meant by the original wording.
Tobias
