Hello,
Fortran 2008 has a build in parallelization (Coarray [Fortran], CAF)
[1]. gfortran did the first steps to a communication-library version
[2]. The library will be based MPI.
There are two issues I like to discuss in this email:
a) configuring and building
b) Test-suite support
Let's start with (b) which is more important for me. The current scheme
is that the user somehow compiles the communication library (libcaf) [2]
and then builds and links doing something like:
mpif90 -fcoarray=lib fortran.f90 -lcaf_mpi
or alternatively
gfortran -fcoarray=lib fortran.f90 -lcaf_mpi
-I/usr/lib64/mpi/gcc/openmpi/include -L/usr/lib64/mpi/gcc/openmpi/lib64
-lmpi
with some -I<dir>, -L<dir> -l<libs> are added. (Cf. "mpif90 -show" of
some MPI implementations.) The resulting program is then run using, e.g.,
mpiexec -n 3 ./a.out
Alternatively, it could be just "-lcaf_single" which is run like normal
("./a.out").
Thus, one needs some means to add link and compile options - and a means
to add an (optional) run command. Those one would probably pass via
environment variables.
One would then either only run the tests if the environment variable is
set - or if "libcaf_single.a" is installed by default (cf. below), one
could default to linking that version if no environment variable is set.
Then "make check-gfortran" could then always run the CAF library checks
- otherwise, only conditionally.
What do you think? Do you have comments how this should be done? I also
wouldn't mind if someone could help as I am not really comfortable with
the test-suite setup nor do I know Lisp well.
Regarding (a): As mentioned above, one could consider compiling, linking
and installing "libcaf_single" by default. libgfortran/caf/single.c is a
simple stub library which essentially does nothing; the only purpose is
to be able to (re)link -fcoarray=lib compile program without recompiling
and for testing and debugging purpose (e.g. for the testsuite?). If one
wants to seriously use a serial program: -fcoarray=single produces much
faster code.
Additionally, there is libgfortran/caf/mpi.c which is an MPI
implementation in a very early stage. (Currently, MPI v2 is required;
however, the plan is to move to an MPI v1 implementation - maybe using
optionally also MPI v2.)
Thus, the first question is: Should one build and install single.c
(libcaf_single.a) by default? (Might also relate to (a), namely how the
test suite is handled.)
And the second question is: Should one be able to configure and build
mpi.c (libcaf_mpi.a) by some means? I think users interested in could
also do the procedure of [2] - or let their admin do it. (For Linux
distributions one would run into the problem that they typically offer
several MPI implementations, e.g. Open MPI and MPICH2, which couldn't be
handled that way.)
(In any case, only static libraries should be created; the libraries
could then be installed in $PREFIX/$lib/gcc/$target/$version/, where
already libgcc.a etc. are located.)
Tobias
[1] http://gcc.gnu.org/wiki/Coarray
[2] http://gcc.gnu.org/wiki/CoarrayLib
PS: At some point there will be also a shared-memory version - maybe for
GCC 4.8.
PPS: Tiny example program - to be compiled with -fcoarray=single -- or
with -fcoarray=lib as described in [2]:
program coarray_example
print *, 'This is image ', this_image(), ' of ', num_images()
end program coarray_example
