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shmem_ptr(3) - Returns a pointer to a data object on a specified
processing element (PE).
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)
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.
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");
}
}
The shmem_ptr function is available only on systems where ordinary
memory loads and stores are used to implement SHMEM put and get operations.
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.
intro_shmem(3), shmem_put(3), shmem_get(3)
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