Provided by: openmpi-doc_2.1.1-8_all 
NAME
shmem_alltoall32(3), shmem_alltoall64(3), shmem_alltoalls32(3), shmem_alltoalls64(3) -
collective routine where each PE exchanges a fixed amount of data with all other PEs in
the Active set
SYNOPSIS
C or C++:
#include <mpp/shmem.h>
void shmem_alltoall32(void *target, const void *source,
size_t nelems, int PE_start, int logPE_stride,
int PE_size, long *pSync);
void shmem_alltoall64(void *target, const void *source,
size_t nelems, int PE_start, int logPE_stride,
int PE_size, long *pSync);
void shmem_alltoalls32(void *target, const void *source,
ptrdiff_t dst, ptrdiff_t sst,
size_t nelems, int PE_start, int logPE_stride,
int PE_size, long *pSync);
void shmem_alltoalls64(void *target, const void *source,
ptrdiff_t dst, ptrdiff_t sst,
size_t nelems, int PE_start, int logPE_stride,
int PE_size, long *pSync);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER dst, sst, nelems, PE_root, PE_start, logPE_stride, PE_size
INTEGER pSync(SHMEM_ALLTOALL_SYNC_SIZE)
CALL SHMEM_ALLTOALL32(target, source, nelems,
& PE_start, logPE_stride, PE_size, fIpSync)
CALL SHMEM_ALLTOALL64(target, source, nelems,
& PE_start, logPE_stride, PE_size, pSync)
CALL SHMEM_ALLTOALLS32(target, source, dst, sst, nelems,
& PE_start, logPE_stride, PE_size, pSync)
CALL SHMEM_ALLTOALLS64(target, source, dst, sst, nelems,
& PE_start, logPE_stride, PE_size, pSync)
DESCRIPTION
The shmem_alltoalls routines are collective routines. Each PE in the Active set exchanges
nelems strided data elements of size 32 bits (for shmem_alltoalls32) or 64 bits (for
shmem_alltoalls64) with all other PEs in the set. Both strides, dst and sst, must be
greater than or equal to 1. The sst*jth block sent from PE i to PE j is placed in the
dst*ith block of the dest data object on PE j. As with all OpenSHMEM collective routines,
these routines assume that only PEs in the Active set call the routine. If a PE not in the
Active set calls an OpenSHMEM collective routine, undefined behavior results. The values
of arguments dst, sst, nelems, PE_start, logPE_stride, and PE_size must be equal on all
PEs in the Active set. The same dest and source data objects, and the same pSync work
array must be passed to all PEs in the Active set. Before any PE calls to a
shmem_alltoalls routine, the following conditions must exist (synchronization via a
barrier or some other method is often needed to ensure this): The pSync array on all PEs
in the Active set is not still in use from a prior call to a shmem_alltoalls routine. The
dest data object on all PEs in the Active set is ready to accept the shmem_alltoalls data.
Upon return from a shmem_alltoalls routine, the following is true for the local PE: Its
dest symmetric data object is completely updated and the data has been copied out of the
source data object. The values in the pSync array are restored to the original values.
The arguments are as follows:
A symmetric data object with one of the following data types:
shmem_alltoall32: Any noncharacter type that
has an element size of 32 bits. No Fortran derived types or C/C++ structures
are allowed.
shmem_alltoall64: Any noncharacter type that has an element size
of 64 bits. No Fortran derived types or C/C++ structures are allowed.
target A symmetric data object large enough to receive the combined total of nelems
elements from each PE in the Active set.
source A symmetric data object that contains nelems elements of data for each PE in the
Active set, ordered according to destination PE.
dst The stride between consecutive elements of the dest data object. The stride is
scaled by the element size. A value of 1 indicates contiguous data. dst must be of
type ptrdiff_t. If you are using Fortran, it must be a default integer value.
sst The stride between consecutive elements of the source data object. The stride is
scaled by the element size. A value of 1 indicates contiguous data. sst must be of
type ptrdiff_t. If you are using Fortran, it must be a default integer value.
nelems The number of elements to exchange for each PE. nelems must be of type size_t for
C/C++. If you are using Fortran, it must be a default integer value
PE_start
The lowest virtual PE number of the active set of PEs. PE_start must be of type
integer. If you are using Fortran, it must be a default integer value.
logPE_stride
The log (base 2) of the stride between consecutive virtual PE numbers in the active
set. log_PE_stride must be of type integer. If you are using Fortran, it must be a
default integer value.
PE_size
The number of PEs in the active set. PE_size must be of type integer. If you are
using Fortran, it must be a default integer value.
pSync A symmetric work array. In C/C++, pSync must be of type long and size
_SHMEM_ALLTOALL_SYNC_SIZE. In Fortran, pSync must be of type integer and size
SHMEM_ALLTOALL_SYNC_SIZE. Every element of this array must be initialized with the
value _SHMEM_SYNC_VALUE (in C/C++) or SHMEM_SYNC_VALUE (in Fortran) before any of
the PEs in the active set enter shmem_barrier().
Upon return from a shmem_alltoalls routine, the following is true for the local PE: Its
dest symmetric data object is completely updated and the data has been copied out of the
source data object. The values in the pSync array are restored to the original values.
The values of arguments PE_root, PE_start, logPE_stride, and PE_size must be equal on all
PEs in the active set. The same target and source data objects and the same pSync work
array must be passed to all PEs in the active set.
Before any PE calls a alltoall routine, you must ensure that the following conditions
exist (synchronization via a barrier or some other method is often needed to ensure this):
The pSync array on all PEs in the active set is not still in use from a prior call to a
alltoall routine. The target array on all PEs in the active set is ready to accept the
alltoall data.
NOTES
The terms collective and symmetric are defined in intro_shmem(3).
All SHMEM alltoall routines restore pSync to its original contents. Multiple calls to
SHMEM routines that use the same pSync array do not require that pSync be reinitialized
after the first call.
You must ensure the that the pSync array is not being updated by any PE in the active set
while any of the PEs participates in processing of a SHMEM broadcast routine. Be careful
to avoid these situations: If the pSync array is initialized at run time, some type of
synchronization is needed to ensure that all PEs in the working set have initialized pSync
before any of them enter a SHMEM routine called with the pSync synchronization array. A
pSync array may be reused on a subsequent SHMEM broadcast routine only if none of the PEs
in the active set are still processing a prior SHMEM alltoall routine call that used the
same pSync array. In general, this can be ensured only by doing some type of
synchronization. However, in the special case of SHMEM routines being called with the
same active set, you can allocate two pSync arrays and alternate between them on
successive calls.
EXAMPLES
C/C++ example:
#include <shmem.h>
#include <stdio.h>
long pSync[SHMEM_ALLTOALL_SYNC_SIZE];
int main(void)
{
int64_t *source, *dest;
int i, count, pe;
shmem_init();
count = 2;
dest = (int64_t*) shmem_malloc(count * shmem_n_pes() * sizeof(int64_t));
source = (int64_t*) shmem_malloc(count * shmem_n_pes() * sizeof(int64_t));
/* assign source values */
for (pe=0; pe <shmem_n_pes(); pe++){
for (i=0; i<count; i++){
source[(pe*count)+i] = shmem_my_pe() + pe;
dest[(pe*count)+i] = 9999;
}
}
for (i=0; i< SHMEM_ALLTOALLS_SYNC_SIZE; i++) {
pSync[i] = SHMEM_SYNC_VALUE;
}
/* wait for all PEs to initialize pSync */
shmem_barrier_all();
/* alltoalls on all PES */
shmem_alltoalls64(dest, source, 1, 1, count, 0, 0, shmem_n_pes(), pSync);
/* verify results */
for (pe=0; pe<shmem_n_pes(); pe++) {
for (i=0; i<count; i++){
if (dest[(pe*count)+i] != shmem_my_pe() + pe) {
printf("[%d] ERROR: dest[%d]=%ld, should be %d0,
shmem_my_pe(),(pe*count)+i,dest[(pe*count)+i],
shmem_n_pes() + pe);
}
}
}
shmem_barrier_all();
shmem_free(dest);
shmem_free(source);
shmem_finalize();
return 0;
}
SEE ALSO
intro_shmem(3)