DeinoMPI

The Great and Terrible implementation of MPI-2

MPI_Address

Gets the address of a location in memory

int MPI_Address(
  void *location,
  MPI_Aint *address
);

Parameters

location: [in] location in caller memory (choice)
address: [out] address of location (integer)

Note

This routine is provided for both the Fortran and C programmers. On many systems, the address returned by this routine will be the same as produced by the C & operator, but this is not required in C and may not be true of systems with word- rather than byte-oriented instructions or systems with segmented address spaces.

The displacements in a general datatype are relative to some initial buffer address. Absolute addresses can be substituted for these displacements: we treat them as displacements relative to "address zero," the start of the address space. This initial address zero is indicated by the constant MPI_BOTTOM. Thus, a datatype can specify the absolute address of the entries in the communication buffer, in which case the buf argument is passed the value MPI_BOTTOM.

Advice to users.

C users may be tempted to avoid the usage of MPI_ADDRESS and rely on the availability of the address operator &. Note, however, that & cast-expression is a pointer, not an address. ANSI C does not require that the value of a pointer (or the pointer cast to int) be the absolute address of the object pointed at --- although this is commonly the case. Furthermore, referencing may not have a unique definition on machines with a segmented address space. The use of MPI_ADDRESS to "reference" C variables guarantees portability to such machines as well.

Thread and Interrupt Safety

This routine is both thread- and interrupt-safe. This means that this routine may safely be used by multiple threads and from within a signal handler.

Deprecated Function

The MPI-2 standard deprecated a number of routines because MPI-2 provides better versions. This routine is one of those that was deprecated. The routine may continue to be used, but new code should use the replacement routine. The replacement for this routine is MPI_Get_address.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierris an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGERin Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS: No error; MPI routine completed successfully.

MPI_ERR_OTHER: Other error; use MPI_Error_string to get more information about this error code.

Example Code

The following sample code illustrates MPI_Get_address because MPI_Address is deprecated.

#include "mpi.h"
#include <stdio.h>

int main( int argc, char *argv[] )
{
    int errs = 0;
    int buf[10];
    MPI_Aint a1, a2;

    MPI_Init( &argc, &argv );

    MPI_Get_address( &buf[0], &a1 );
    MPI_Get_address( &buf[1], &a2 );

    if ((int)(a2-a1) != sizeof(int)) {
        errs++;
        printf( "Get address of two address did not return values the correct distance apart\n" );fflush(stdout);
    }
    MPI_Finalize();
    return 0;
}

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