MPI_Buffer_detach(3) Open MPI MPI_Buffer_detach(3)
NAME
MPI_Buffer_detach - Removes an existing buffer (for use in 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
C++ Syntax
#include <mpi.h>
int Detach_buffer(void*& buffer)
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 MPI_Buffer_detach returns the address and size of the
buffer being detached is to allow nested libraries to replace and re-
store 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 weaknesses (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 MPI_Buffer_attach and MPI_Buffer_detach
both have a first argument of type void*, these arguments are used dif-
ferently: A pointer to the buffer is passed to MPI_Buffer_attach; the
address of the pointer is passed to MPI_Buffer_detach, so that this
call can return the pointer value.
ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument. C++ func-
tions do not return errors. If the default error handler is set to
MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
will be used to throw an MPI::Exception object.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
may be used to cause error values to be returned. Note that MPI does
not guarantee that an MPI program can continue past an error.
SEE ALSO
MPI_Buffer_attach
MPI_Bsend
4.1.2 Nov 24, 2021 MPI_Buffer_detach(3)
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