Ubuntu Manpage: shmem_int_or_to_all(3), shmem_int4_or_to_all(3), shmem_int8_or_to

Provided by: openmpi-doc_1.10.2-8ubuntu1_all

NAME

       shmem_int_or_to_all(3),          shmem_int4_or_to_all(3),         shmem_int8_or_to_all(3),
       shmem_long_or_to_all(3), shmem_longlong_or_to_all(3), shmem_short_or_to_all(3) -  Performs
       a bitwise OR function reduction across a set of processing elements (PEs)

SYNOPSIS

       C or C++:
       #include <mpp/shmem.h>

       void shmem_int_or_to_all(int *target, int *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         int *pWrk, long *pSync);

       void shmem_long_or_to_all(long *target, long *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         long *pWrk, long *pSync);

       void shmem_longlong_or_to_all(long long *target,
         long long *source, int nreduce, int PE_start, int logPE_stride,
         int PE_size, long long *pWrk, long *pSync);

       void shmem_short_or_to_all(short *target, 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_OR_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_INT8_OR_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

DESCRIPTION

The shared memory (SHMEM) reduction routines compute one or more reductions across
symmetric arrays on multiple virtual PEs. A reduction performs an associative binary
operation across a set of values. For a list of other SHMEM reduction routines, see
intro_shmem(3).

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 nreduce argument determines the number of separate reductions to perform. The source
array on all PEs in the active set provides one element 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 defined 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.

The arguments are as follows:

target A symmetric array of length nreduce elements to receive the results 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_or_to_all Integer, with an element size of 8 bytes.

shmem_int4_or_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 argument 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 integer. 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 contains max(nreduce/2 + 1,
SHMEM_REDUCE_MIN_WRKDATA_SIZE) elements.

pSync A symmetric work array. In C/C++, pSync is of type long and size
_SHMEM_REDUCE_SYNC_SIZE. In Fortran, pSync is of type integer and size
SHMEM_REDUCE_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 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 following 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: 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  intro_shmem(3).   All
       SHMEM  reduction  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 reduction 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  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 doing some type of
       synchronization. However, in the special case of reduction routines being called with  the
       same  active set, you can allocate 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 OR 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, FOOOR
       COMMON /COM/ FOO, FOOOR, PWRK
       INTRINSIC MY_PE

       IF ( MOD(MY_PE(),2) .EQ. 0) THEN
         CALL SHMEM_INT8_OR_TO_ALL(FOOOR, FOO, NR, 0, 1, N$PES/2,
         & PWRK, PSYNC)
         PRINT *,'Result on PE ',MY_PE(),' is ',FOOOR
       ENDIF

       Example 2: Consider the following C/C++ call:
       shmem_int_or_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_or_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
         pwrk1, psync1);
       shmem_int_or_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
         pwrk2, psync2);
       shmem_int_or_to_all(&(target[2]), &(source[2]), 1, 0, 0, 8,
         pwrk1, psync1);

       Note  that  two  sets  of  pWrk  and  pSync  arrays  are  used  alternately   because   no
       synchronization is done between calls.

NAME

SYNOPSIS

DESCRIPTION

NOTES

EXAMPLES

SEE ALSO