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MPI_Buffer_detach

:ref:`MPI_Buffer_detach` |mdash| Removes an existing buffer (for use in in :ref:`MPI_Bsend`, etc.)

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Buffer_detach(void *buf, int *size)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_BUFFER_DETACH(BUF, SIZE, IERROR)
    <type>  BUF(*)
    INTEGER SIZE, IERROR

Fortran 2008 Syntax

USE mpi_f08

MPI_Buffer_detach(buffer_addr, size, ierror)
    USE, INTRINSIC :: ISO_C_BINDING, ONLY
    TYPE(C_PTR), INTENT(OUT) :: buffer_addr
    INTEGER, INTENT(OUT) :: size
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

OUTPUT PARAMETERS

  • buf : Initial buffer address (choice).
  • size : Buffer size, in bytes (integer).
  • ierror : Fortran only: Error status (integer).

DESCRIPTION

Detach the buffer currently associated with MPI. The call returns the address and the size of the detached buffer. This operation will block until all messages currently in the buffer have been transmitted. Upon return of this function, the user may reuse or deallocate the space taken by the buffer.

Example: Calls to attach and detach buffers.

#define BUFFSIZE 10000

int size char *buff;
MPI_Buffer_attach( malloc(BUFFSIZE), BUFFSIZE);

// a buffer of 10000 bytes can now be used by MPI_Bsend

MPI_Buffer_detach( &buff, &size); // Buffer size reduced to zero
MPI_Buffer_attach( buff, size); // Buffer of 10000 bytes available again

NOTES

The reason that :ref:`MPI_Buffer_detach` returns the address and size of the buffer being detached is to allow nested libraries to replace and restore the 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 same strengths (it's simple) and weak‐nesses (it only works for nested usages).

For Fortran: The Fortran binding for this routine is different. Because Fortran does not have pointers, it is impossible to provide a way to use the output of this routine to exchange buffers. In this case, only the size field is set.

For C: Even though the buf argument is declared as void, it is really the address of a void pointer. See Rationale, below, for more details.

Even though the C functions :ref:`MPI_Buffer_attach` and :ref:`MPI_Buffer_detach` both have a first argument of type void*, these arguments are used differently: A pointer to the buffer is passed to :ref:`MPI_Buffer_attach`; the address of the pointer is passed to :ref:`MPI_Buffer_detach`, so that this call can return the pointer value.

ERRORS

.. seealso::
   * :ref:`MPI_Buffer_attach`