Ubuntu Manpage: shmem_int_and_to_all(3), shmem_int4_and_to_all(3), shmem_int8_and_to_all(3), shmem_long_and_to

Provided by: openmpi-doc_4.1.6-7ubuntu2_all

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_longlong_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 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).

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. 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, 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 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 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 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 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 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 the following 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 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  because  no  synchronization  is  done
       between calls.

NAME

SYNOPSIS

DESCRIPTION

NOTES

EXAMPLES

SEE ALSO