Synopsis
int MPI_Buffer_detach(void *buffer_addr, int *size)int MPI_Buffer_detach_c(void *buffer_addr, MPI_Count *size)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
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 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
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.
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.
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.
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 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.
Errors
All MPI routines (except 'MPI_Wtime' and 'MPI_Wtick') return an error value;
C routines as the value of the function and Fortran routines in the last
argument. Before the value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job. The error handler
may be changed with 'MPI_Comm_set_errhandler' (for communicators),
'MPI_File_set_errhandler' (for files), and 'MPI_Win_set_errhandler' (for
RMA windows). The MPI-1 routine 'MPI_Errhandler_set' may be used but
its use is deprecated. 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; however, MPI implementations will attempt to continue whenever
possible.
-
MPI_SUCCESS - No error; MPI routine completed successfully.
-
MPI_ERR_ARG - Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., 'MPI_ERR_RANK').
-
MPI_ERR_OTHER - Other error; use 'MPI_Error_string' to get more information about this error code.