openmpi/oshmem/shmem/man/man3/shmem_ptr.3in

.\" -*- nroff -*-
.\" Copyright (c) 2015      University of Houston.  All rights reserved.
.\" Copyright (c) 2015      Mellanox Technologies, Inc.
.\" $COPYRIGHT$
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.TH "SHMEM\\_PTR" "3" "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
.SH NAME

\fIshmem_ptr\fP(3)
\- Returns a pointer to a data object on a specified processing element
(PE).
.SH SYNOPSIS

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

void *shmem_ptr(void *target, int pe);
.Ve
Fortran:
.Vb
INCLUDE "mpp/shmem.fh"

POINTER (PTR, POINTEE)
INTEGER pe

PTR = SHMEM_PTR(target, pe)
.Ve
.SH DESCRIPTION

The shmem_ptr routine returns an address that can be used to directly reference
\fBtarget\fP
on the remote PE \fBpe\fP\&.
With this address we can perform ordinary loads
and stores to the remote address.
.PP
When a sequence of loads (gets) and stores (puts) to a data object on a remote PE does not
match the access pattern provided in a SHMEM data transfer routine like
\fIshmem_put32\fP(3)
or \fIshmem_real_iget\fP(3),
the shmem_ptr function can
provide an efficient means to accomplish the communication.
.PP
The arguments are as follows:
.TP
target
The symmetric data object to be referenced.
.TP
pe
An integer that indicates the PE number on which target is to be accessed. If you
are using Fortran, it must be a default integer value.
.PP
.SH EXAMPLES

This Fortran program calls shmem_ptr and then PE 0 writes to the BIGD array on PE 1:
.Vb
PROGRAM REMOTEWRITE
  INCLUDE 'mpp/shmem.fh'

  INTEGER BIGD(100)
  SAVE BIGD
  INTEGER POINTEE(*)

  POINTER (PTR,POINTEE)
  CALL START_PES(0)
  IF (MY_PE() .EQ. 0) THEN
                             ! initialize PE 1's BIGD array
    PTR = SHMEM_PTR(BIGD, 1) ! get address of PE 1's BIGD
                             ! array
    DO I=1,100
      POINTEE(I) = I
    ENDDO
  ENDIF
  CALL SHMEM_BARRIER_ALL
  IF (MY_PE() .EQ. 1) THEN
    PRINT *, 'BIGD on PE 1 is: '
    PRINT *, BIGD
  ENDIF
END
.Ve
This is the equivalent program written in C:
.Vb
#include <mpp/shmem.h>
main()
{
  static int bigd[100];
  int *ptr;
  int i;

  shmem_init();
  if (shmem_my_pe() == 0) {
  /* initialize PE 1's bigd array */
    ptr = shmem_ptr(bigd, 1);
    for (i=0; i<100; i++)
      *ptr++ = i+1;
  }
  shmem_barrier_all();
  if (shmem_my_pe() == 1) {
    printf("bigd on PE 1 is:\\n");
    for (i=0; i<100; i++)
      printf(" %d\\n",bigd[i]);
    printf("\\n");
  }
}
.Ve
.SH NOTES

The shmem_ptr function is available only on systems where ordinary memory loads and
stores are used to implement SHMEM put and get operations.
.PP
.SH RETURN VALUES

shmem_ptr returns a pointer to the data object on the specified remote PE. If target is not
remotely accessible, a NULL pointer is returned.
.PP
.SH SEE ALSO

\fIintro_shmem\fP(3),
\fIshmem_put\fP(3),
\fIshmem_get\fP(3)
.PP