18.2.178. shmem_ptr — Open MPI 5.0.8 documentation

# 18.2.178. shmem_ptr

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

## 18.2.178.1. 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)

## 18.2.178.2. 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:

target

  The symmetric data object to be referenced.

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.

## 18.2.178.3. 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");
      }
    }

## 18.2.178.4. 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.

## 18.2.178.5. 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)