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SHMEM_PTR(3) Open MPI SHMEM_PTR(3)

shmem_ptr(3) - Returns a pointer to a data object on a specified processing element (PE).

SYNOPSIS

C or C++:

#include <mpp/shmem.h>
void *shmem_ptr(const void *target, int pe)


Fortran:

INCLUDE "mpp/shmem.fh"
POINTER (PTR, POINTEE)
INTEGER pe
PTR = SHMEM_PTR(target, pe)


DESCRIPTION

The shmem_ptr routine returns an address that can be used to directly reference target on the remote PE pe. With this address we can perform ordinary loads and stores to the remote address.

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 shmem_put32(3) or shmem_real_iget(3), the shmem_ptr function can provide an efficient means to accomplish the communication.

The arguments are as follows:

The symmetric data object to be referenced.
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.

EXAMPLES

This Fortran program calls shmem_ptr and then PE 0 writes to the BIGD array on PE 1:

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


This is the equivalent program written in C:

#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");


  }
}


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.

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.

SEE ALSO:

intro_shmem(3) shmem_put(3) shmem_get(3)


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December 2, 2024