MPI_Buffer_detach

Removes an existing buffer (for use in MPI_Bsend etc)

Synopsis

#include "mpi.h"
int MPI_Buffer_detach( bufferptr, size )
void *bufferptr;
int  *size;

Output Parameters

	buffer	initial buffer address (choice)
	size	buffer size, in bytes (integer)

Notes

The reason that MPI_Buffer_detach returns the address and size of thebuffer being detached is to allow nested libraries to replace and restorethe buffer. For example, consider

    int size, mysize, idummy;
    void *ptr, *myptr, *dummy;     
    MPI_Buffer_detach( &ptr, &size );
    MPI_Buffer_attach( myptr, mysize );
    ...
    ... library code ...
    ...
    MPI_Buffer_detach( &dummy, &idummy );
    MPI_Buffer_attach( ptr, size );

This is much like the action of the Unix signal routine and has the samestrengths (it is simple) and weaknesses (it only works for nested usages).

Note that for this approach to work, MPI_Buffer_detach must return MPI_SUCCESSeven when there is no buffer to detach. In that case, it returns a size ofzero. The MPI 1.1 standard for MPI_BUFFER_DETACH contains the text

   The statements made in this section describe the behavior of MPI for
   buffered-mode sends. When no buffer is currently associated, MPI behaves 
   as if a zero-sized buffer is associated with the process.

This could be read as applying only to the various Bsend routines. Thisimplementation takes the position that this applies to MPI_BUFFER_DETACHas well.

Notes for Fortran

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

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

The Fortran binding for this routine is different. Because Fortrandoes not have pointers, it is impossible to provide a way to use theoutput of this routine to exchange buffers. In this case, only thesize field is set.

Notes for C

Even though the bufferptr argument is declared as void *, it isreally the address of a void pointer. See the rationale in thestandard for more details.

Location:buffree.c