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MPI_Buffer_detach(3) MPI MPI_Buffer_detach(3)
MPI_Buffer_detach - Removes an existing buffer (for use in MPI_Bsend
int MPI_Buffer_detach(void *buffer, int *size)
buffer - initial buffer address (choice)
size - buffer size, in bytes (integer)
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
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 is simple) and weaknesses (it only works for nested
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
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.
This implementation takes the position that this applies to
MPI_BUFFER_DETACH as well.
THREAD AND INTERRUPT SAFETY
The user is responsible for ensuring that multiple threads do not try
to update the same MPI object from different threads. This routine
should not be used from within a signal handler.
The MPI standard defined a thread-safe interface but this does not mean
that all routines may be called without any thread locks. For example,
two threads must not attempt to change the contents of the same
MPI_Info object concurrently. The user is responsible in this case for
using some mechanism, such as thread locks, to ensure that only one
thread at a time makes use of this routine. 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 .
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. ierr is
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 INTEGER in
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