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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:
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 ENDThis 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)