SHMEM_BROADCAST(3) Open MPI SHMEM_BROADCAST(3)
NAME
shmem_broadcast4(3), shmem_broadcast8(3), shmem_broadcast32(3),
shmem_broadcast64(3) - Copy a data object from a designated PE to a
target location on all other PEs of the active set.
SYNOPSIS
C or C++:
#include <mpp/shmem.h>
void shmem_broadcast32(void *target, const void *source,
size_t nelems, int PE_root, int PE_start, int logPE_stride,
int PE_size, long *pSync);
void shmem_broadcast64(void *target, const void *source,
size_t nelems, int PE_root, int PE_start, int logPE_stride,
int PE_size, long *pSync);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER nelems, PE_root, PE_start, logPE_stride, PE_size
INTEGER pSync(SHMEM_BCAST_SYNC_SIZE)
CALL SHMEM_BROADCAST4(target, source, nelems, PE_root,
& PE_start, logPE_stride, PE_size, fIpSync)
CALL SHMEM_BROADCAST8(target, source, nelems, PE_root,
& PE_start, logPE_stride, PE_size, pSync)
CALL SHMEM_BROADCAST32(target, source, nelems,
& PE_root, PE_start, logPE_stride, PE_size, pSync)
CALL SHMEM_BROADCAST64(target, source, nelems,
& PE_root, PE_start, logPE_stride, PE_size, pSync)
DESCRIPTION
The broadcast routines write the data at address source of the PE spec-
ified by PE_root to address target on all other PEs in the active set.
The active set of PEs is defined by the triplet PE_start, logPE_stride
and PE_size. The data is not copied to the target address on the PE
specified by PE_root. Before returning, the broadcast routines ensure
that the elements of the pSync array are restored to their initial val-
ues.
As with all SHMEM collective routines, each of these routines assumes
that only PEs in the active set call the routine. If a PE not in the
active set calls a SHMEM collective routine, undefined behavior re-
sults.
The arguments are as follows:
target A symmetric data object with one of the following data types:
shmem_broadcast8, shmem_broadcast64: Any noncharacter type that
has an element size of 64 bits. No Fortran derived types
or C/C++ structures are allowed.
shmem_broadcast32: Any noncharacter type that has an element
size
of 32 bits. No Fortran derived types or C/C++ structures
are allowed.
shmem_broadcast4: Any noncharacter type that has an element size
of 32 bits.
source A symmetric data object that can be of any data type that is
permissible for the target argument.
nelems The number of elements in source. For shmem_broadcast32 and
shmem_broadcast4, this is the number of 32-bit halfwords. nelems
must be of type integer. If you are using Fortran, it must be a
default integer value.
PE_root
Zero-based ordinal of the PE, with respect to the active set,
from which the data is copied. Must be greater than or equal to
0 and less than PE_size. PE_root must be of type integer. 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 inte-
ger. 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 in-
teger. 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_BCAST_SYNC_SIZE. In Fortran, pSync must be of type
integer and size SHMEM_BCAST_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().
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 broadcast routine, you must ensure that the fol-
lowing 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 broadcast
routine. The target array on all PEs in the active set is ready to ac-
cept the broadcast data.
Upon return from a broadcast routine, the following are true for the
local PE: If the current PE is not the root PE, the target data object
is updated. The values in the pSync array are restored to the original
values.
NOTES
The terms collective and symmetric are defined in intro_shmem(3).
All SHMEM broadcast 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 synchro-
nization 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 broadcast 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
In the following examples, the call to shmem_broadcast64 copies source
on PE 4 to target on PEs 5, 6, and 7.
C/C++ example:
for (i=0; i < _SHMEM_BCAST_SYNC_SIZE; i++) {
pSync[i] = _SHMEM_SYNC_VALUE;
}
shmem_barrier_all(); /* Wait for all PEs to initialize pSync */
shmem_broadcast64(target, source, nelems, 0, 4, 0, 4, pSync);
Fortran example:
INTEGER PSYNC(SHMEM_BCAST_SYNC_SIZE)
INTEGER TARGET, SOURCE, NELEMS, PE_ROOT, PE_START,
& LOGPE_STRIDE, PE_SIZE, PSYNC
COMMON /COM/ TARGET, SOURCE
DATA PSYNC /SHMEM_BCAST_SYNC_SIZE*SHMEM_SYNC_VALUE/
CALL SHMEM_BROADCAST64(TARGET, SOURCE, NELEMS, 0, 4, 0, 4,
& PSYNC)
SEE ALSO
intro_shmem(3)
4.1.2 Nov 24, 2021 SHMEM_BROADCAST(3)
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