From the MPI 3.1 standard (page 338)
Rationale. The C bindings of MPI_ALLOC_MEM and MPI_FREE_MEM are similar
to the bindings for the malloc and free C library calls: a call to
MPI_Alloc_mem(: : :, &base) should be paired with a call to
MPI_Free_mem(base) (one
less level of indirection). Both arguments are declared to be of same type
void* so as to facilitate type casting. The Fortran binding is
consistent with the C
bindings: the Fortran MPI_ALLOC_MEM call returns in baseptr the
TYPE(C_PTR)
pointer or the (integer valued) address of the allocated memory. The
base argument
of MPI_FREE_MEM is a choice argument, which passes (a reference to)
the variable
stored at that location. (End of rationale.)
at first glance, i also thought type should have been char ** instead of
char *, but it is not a typo nor a mistake
Cheers,
Gilles
On 10/27/2016 5:13 PM, Bader, Reinhold wrote:
I've had a look at the OpenMPI 1.10.3 sources, and the trouble appears
to me to be that the MPI wrappers declare
the argument
TYPE(C_PTR), INTENT(OUT) :: baseptr
inside the BIND(C) interface on the Fortran side (for OpenMPI this
would, for example be ompi_win_allocate_f), and
the C implementation has "char *baseptr" as parameter. This is
incorrect, it needs to be
char **baseptr
I believe this actually points to a design weakness of the C-side
interface. For establishment of a C pointer, usually
functions that return such a pointer are defined (e.g. malloc()). If a
formal parameter is desired, this should be
a pointer-to-pointer entity, i.e. it would have been better to define
the MPI_Win_allocate prototype as
int MPI_Win_allocate(MPI_Aint size, int disp_unit, MPI_Info info,
MPI_comm comm, *void **baseptr*, MPI_Win win);
Note that the C example pretends that this is the case – it passes the
address of the pointer to
MPI_Win_allocate, not the pointer itself.
Cheers
--
Dr. Reinhold Bader
Leibniz Supercomputing Centre (http://www.lrz.de) / HPC Systems and
Services
Tel.: 0049 89 35831 8825 Fax: 8625
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