SHMEM_AND(3) Open MPI SHMEM_AND(3)
NAME
shmem_int_and_to_all(3), shmem_int4_and_to_all(3),
shmem_int8_and_to_all(3), shmem_long_and_to_all(3), shmem_long-
long_and_to_all(3), shmem_short_and_to_all(3) - Performs a bitwise AND
operation on symmetric arrays over the active set of PEs.
SYNOPSIS
C or C++:
#include <mpp/shmem.h>
void shmem_int_and_to_all(int *target, const int *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
int *pWrk, long *pSync);
void shmem_long_and_to_all(long *target, const long *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
long *pWrk, long *pSync);
void shmem_longlong_and_to_all(long long *target,
const long long *source, int nreduce, int PE_start, int logPE_stride,
int PE_size, long long *pWrk, long *pSync);
void shmem_short_and_to_all(short *target, const short *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
short *pWrk, long *pSync);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER pSync(SHMEM_REDUCE_SYNC_SIZE)
INTEGER nreduce, PE_start, logPE_stride, PE_size
CALL SHMEM_INT4_AND_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_INT8_AND_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
DESCRIPTION
The shared memory (SHMEM) reduction routines compute one or more reduc-
tions across symmetric arrays on multiple virtual PEs. A reduction per-
forms an associative binary operation across a set of values. For a
list of other SHMEM reduction routines, see intro_shmem(3).
The nreduce argument determines the number of separate reductions to
perform. The source array on all PEs in the active set provides one el-
ement for each reduction. The results of the reductions are placed in
the target array on all PEs in the active set. The active set is de-
fined by the PE_start, logPE_stride, PE_size triplet.
The source and target arrays may be the same array, but they may not be
overlapping arrays. As with all SHMEM collective routines, each of
these routines assumes that only PEs in the active set call the rou-
tine. 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, of length nreduce elements, to receive the
result of the reduction operations. The data type of target
varies with the version of the reduction routine being called.
When calling from C/C++, refer to the SYNOPSIS section for data
type information. When calling from Fortran, the target data
types are as follows:
shmem_int8_and_to_all: Integer, with an element size of 8 bytes
shmem_int4_and_to_all: Integer, with an element size of 4 bytes
source A symmetric array, of length nreduce elements, that contains one
element for each separate reduction operation. The source argu-
ment must have the same data type as target.
nreduce
The number of elements in the target and source arrays. nreduce
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 in-
teger. If you are using Fortran, it must be a default integer
value.
pWrk A symmetric work array. The pWrk argument must have the same
data type as target. In C/C++, this contains max(nreduce/2 + 1,
_SHMEM_REDUCE_MIN_WRKDATA_SIZE) elements. In Fortran, this con-
tains max(nreduce/2 + 1, SHMEM_REDUCE_MIN_WRKDATA_SIZE) ele-
ments.
pSync A symmetric work array. In C/C++, pSync must be of type long and
size _SHMEM_REDUCE_SYNC_SIZE. In Fortran, pSync must be of type
integer and size SHMEM_REDUCE_SYNC_SIZE. If you are using For-
tran, 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 the reduction routine.
The values of arguments nreduce, 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 pWrk and pSync work arrays, must be passed to all
PEs in the active set.
Before any PE calls a reduction 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 pWrk and pSync arrays on
all PEs in the active set are not still in use from a prior call to a
collective SHMEM routine. The target array on all PEs in the active set
is ready to accept the results of the reduction.
Upon return from a reduction 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.
NOTES
The terms collective, symmetric, and cache aligned are defined in in-
tro_shmem(3). All SHMEM reduction routines reset the values in pSync
before they return, so a particular pSync buffer need only be initial-
ized 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 reduction routine. Be careful to avoid the following situations:
If the pSync array is initialized at run time, some type of synchro-
nization is needed to ensure that all PEs in the working set have ini-
tialized pSync before any of them enter a SHMEM routine called with the
pSync synchronization array. A pSync or pWrk array can be reused in a
subsequent reduction routine call only if none of the PEs in the active
set are still processing a prior reduction routine call that used the
same pSync or pWrk arrays. In general, this can be assured only by do-
ing some type of synchronization. However, in the special case of re-
duction routines being called with the same active set, you can allo-
cate two pSync and pWrk arrays and alternate between them on successive
calls.
EXAMPLES
Example 1: This Fortran example statically initializes the pSync array
and finds the logical AND of the integer variable FOO across all even
PEs.
INCLUDE "mpp/shmem.fh"
INTEGER PSYNC(SHMEM_REDUCE_SYNC_SIZE)
DATA PSYNC /SHMEM_REDUCE_SYNC_SIZE*SHMEM_SYNC_VALUE/
PARAMETER (NR=1)
REAL PWRK(MAX(NR/2+1, SHMEM_REDUCE_MIN_WRKDATA_SIZE))
INTEGER FOO, FOOAND
COMMON /COM/ FOO, FOOAND, PWRK
INTRINSIC MY_PE
IF ( MOD(MY_PE(),2) .EQ. 0) THEN
CALL SHMEM_INT8_AND_TO_ALL(FOOAND, FOO, NR, 0, 1, N$PES/2,
& PWRK, PSYNC)
PRINT *, 'Result on PE ', MY_PE(), ' is ', FOOAND
ENDIF
Example 2: Consider the following C call:
shmem_int_and_to_all( target, source, 3, 0, 0, 8, pwrk, psync );
The preceding call is more efficient, but semantically equivalent to,
the combination of the following calls:
shmem_int_and_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
pwrk1, psync1);
shmem_int_and_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
pwrk2, psync2);
shmem_int_and_to_all(&(target[2]), &(source[2]), 1, 0, 0, 8,
pwrk1, psync1);
Note that two sets of pWrk and pSync arrays are used alternately be-
cause no synchronization is done between calls.
SEE ALSO
f90(1), intro_shmem(3)
4.1.2 Nov 24, 2021 SHMEM_AND(3)
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