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Table of Contents
shmem_collect4(3), shmem_collect8(3), shmem_collect32(3), shmem_collect64(3),
shmem_fcollect(3), shmem_fcollect4(3), shmem_fcollect8(3), shmem_fcollect32(3),
shmem_fcollect64(3) - Concatenates blocks of data from multiple processing
elements (PEs) to an array in every PE
C or C++:
#include <mpp/shmem.h>
void shmem_collect32(void *target, const void *source,
size_t nelems, int PE_start, int logPE_stride, int PE_size,
long *pSync);
void shmem_collect64(void *target, const void *source,
size_t nelems, int PE_start, int logPE_stride, int PE_size,
long *pSync);
void shmem_fcollect32(void *target, const void *source,
size_t nelems, int PE_start, int logPE_stride, int PE_size,
long *pSync);
void shmem_fcollect64(void *target, const void *source,
size_t nelems, int PE_start, int logPE_stride, int PE_size,
long *pSync);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER nelems
INTEGER PE_start, logPE_stride, PE_size
INTEGER pSync(SHMEM_COLLECT_SYNC_SIZE)
CALL SHMEM_COLLECT4(target, source, nelems, PE_start,
& logPE_stride, PE_size, pSync)
CALL SHMEM_COLLECT8(target, source, nelems, PE_start,
& logPE_stride, PE_size, pSync)
CALL SHMEM_FCOLLECT4(target, source, nelems, PE_start,
& logPE_stride, PE_size, pSync)
CALL SHMEM_FCOLLECT8(target, source, nelems, PE_start,
& logPE_stride, PE_size, pSync)
The shared memory (SHMEM) collect and fcollect routines concatenate
nelems 64-bit or 32-bit data items from the source array into the target
array, over the set of PEs defined by PE_start, log2PE_stride, and PE_size,
in processor number order. The resultant target array contains the contribution
from PE PE_start first, then the contribution from PE PE_start + PE_stride
second, and so on. The collected result is written to the target array for
all PEs in the active set.
The fcollect routines require that nelems be
the same value in all participating PEs, while the collect routines allow
nelems to vary from PE to PE.
The resulting target array is as follows:
----------------------------------------------------------
source(1..nelems)
from PE (PE_start + 0 * (2**logPE_stride))
----------------------------------------------------------
source(1..nelems)
from PE (PE_start + 1 * (2**logPE_stride))
----------------------------------------------------------
...
----------------------------------------------------------
source(1..nelems) from
PE (PE_start + (PE_size - 1) * (2**logPE_stride))
----------------------------------------------------------
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 results.
The arguments
are as follows:
- target
- A symmetric array. The target argument must be large
enough to accept the concatenation of the source arrays on all PEs. The
data types are as follows:
- [shmem_collect8, shmem_collect64, shmem_fcollect8,
and
- shmem_fcollect64] any data type with an element size of 64 bits. Fortran
derived types, Fortran character type, and C/C++ structures are not permitted.
- [shmem_collect4, shmem_collect32, shmem_fcollect4, and
- shmem_fcollect32]
any data type with an element size of 32 bits. Fortran derived types, Fortran
character type, and C/C++ structures are not permitted.
- source
- A symmetric
data object that can be of any type permissible for the target argument.
- nelems
- The number of elements in the source array. nelems 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. logPE_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 int and size _SHMEM_COLLECT_SYNC_SIZE. In
Fortran, pSync must be of type integer and size SHMEM_COLLECT_SYNC_SIZE.
If you are using Fortran, it must be a default integer value. 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_start, logPE_stride, and
PE_size must be equal on all PEs in the active set. The same target and
source arrays and the same pSync work array must be passed to all PEs in
the active set.
Upon return from a collective routine, the following are
true for the local PE: The target array is updated. The values in the pSync
array are restored to the original values.
The terms collective and
symmetric are defined in intro_shmem(3). All SHMEM collective routines reset
the values in pSync before they return, so a particular pSync buffer need
only be initialized the first time it is used.
You must ensure that the
pSync array is not being updated on any PE in the active set while any
of the PEs participate in processing of a SHMEM collective 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 can be reused on a subsequent
SHMEM collective routine only if none of the PEs in the active set are
still processing a prior SHMEM collective routine call that used the same
pSync array. In general, this may 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.
The collective routines operate on active
PE sets that have a non-power-of-two PE_size with some performance degradation.
They operate with no performance degradation when nelems is a non-power-of-two
value.
C/C++:
for (i=0; i < _SHMEM_COLLECT_SYNC_SIZE; i++) {
pSync[i] = _SHMEM_SYNC_VALUE;
}
shmem_barrier_all(); /* Wait for all PEs to initialize pSync */
shmem_collect32(target, source, 64, pe_start, logPE_stride,
pe_size, pSync);
Fortran:
INTEGER PSYNC(SHMEM_COLLECT_SYNC_SIZE)
DATA PSYNC /SHMEM_COLLECT_SYNC_SIZE*SHMEM_SYNC_VALUE/
CALL SHMEM_COLLECT4(TARGET, SOURCE, 64, PE_START,
& LOGPE_STRIDE, PE_SIZE, PSYNC)
intro_shmem(3)
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