Dear OpenMPI Experts
I am having trouble compiling code with MPI_STARTALL using
OpenMPI 1.4.2 mpif90 built with gcc (4.1.2) and Intel ifort (10.1.017),
when the array of requests is multi-dimensional.
It gives me this error message:
**************************
fortcom: Error: mpiwrap_mod.F90, line 478: There is no matching specific
subroutine for this generic subroutine call. [MPI_STARTALL]
call MPI_STARTALL(nreq,req,ierr)
---------^
**************************
However, if I replace MPI_STARTALL by a loop that calls
MPI_START repeated times, the compilation succeeds.
I wonder if the serialization imposed by the loop may
have some performance impact,
or if MPI_STARTALL just implements the same type of loop.
Another workaround is to declare my array of requests
as a one-dimensional assumed-size array inside my subroutine.
The problem seems to be that MPI_STARTALL doesn't handle
multi-dimensional arrays of requests.
I can live with either workaround above,
but is this supposed to be so?
***
I poked around on the OpenMPI code in ompi/mpi/f90/scripts
and I found out that several OpenMPI Fortran90 subroutines
have code to handle arrays up to rank 7 (the Fortran90 maximum),
mostly for the send and receive buffers.
However, other subroutines and other array arguments, which can also
legitimately be multi-dimensional arrays, are not treated the same way.
In particular, there is only one (assumed-size) dimension for the
array of requests in MPI_STARTALL, for instance.
MPI_WAITALL is another example of restriction,
but there are probably other examples,
most likely on those subroutines that take request and status arrays.
I guess it would be nice if all OpenMPI
subroutines in the Fortran90 bindings would accept
arrays of rank up to 7 on all of their array dummy arguments.
Assuming this doesn't violate the MPI standard, of course.
This would allow more flexibility when writing MPI programs
in Fortran90.
***
More details:
This is the code that fails to compile (np is global in the module):
***********************************
subroutine mpiwrap_startall(req)
integer, dimension(0:np-1,0:1), intent(inout) :: req
integer, parameter :: nreq = 2*np
integer :: ierr
call MPI_STARTALL(nreq,req,ierr)
end subroutine mpiwrap_startall
********************************
This code that compiles:
*****************************
subroutine mpiwrap_startall(req)
integer, dimension(0:np-1,0:1), intent(inout) :: req
integer :: pp, ii
integer :: ierr
do ii=0,1
do pp=0,np-1
call MPI_START(req(ii,pp),ierr)
enddo
enddo
end subroutine mpiwrap_startall
*********************************
This is yet another code that compiles:
*********************************
subroutine mpiwrap_startall(req)
! dummy arguments
integer, dimension(*), intent(inout) :: req
integer, parameter :: nreq = 2*np
integer :: ierr
call MPI_STARTALL(nreq,req,ierr)
end subroutine mpiwrap_startall
*********************************
Many thanks,
Gus Correa
