/*D
   MPI_Buffer_detach - Removes an existing buffer (for use in MPI_Bsend etc)

Synopsis:
.vb
int MPI_Buffer_detach(void *buffer_addr, int *size)
.ve
.vb
int MPI_Buffer_detach_c(void *buffer_addr, MPI_Count *size)
.ve

Output Parameters:
+ buffer_addr - initial buffer address (choice)
- size - buffer size, in bytes (integer)

Notes:
    The reason that '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

.vb
    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);
.ve

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

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

.vb
   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.
.ve

This could be read as applying only to the various Bsend routines.  This
implementation takes the position that this applies to 'MPI_BUFFER_DETACH'
as well.

.N NotThreadSafe
Because the buffer for buffered sends (e.g., 'MPI_Bsend') is shared by all
threads in a process, the user is responsible for ensuring that only
one thread at a time calls this routine or 'MPI_Buffer_attach'.

.N 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.

Notes for C:
    Even though the 'bufferptr' argument is declared as 'void *', it is
    really the address of a void pointer.  See the rationale in the
    standard for more details.

.N Errors
.N MPI_SUCCESS
.N MPI_ERR_ARG
.N MPI_ERR_OTHER

.seealso: MPI_Buffer_attach
D*/

