MPI_Buffer_attach
Attaches a user-provided buffer for sending
Synopsis
int MPI_Buffer_attach(void *buffer, int size)
Input Parameters
- buffer
- initial buffer address (choice)
- size
- buffer size, in bytes (integer)
Notes
The size given should be the sum of the sizes of all outstanding Bsends that
you intend to have, plus MPI_BSEND_OVERHEAD for each Bsend that you do.
For the purposes of calculating size, you should use MPI_Pack_size.
In other words, in the code
MPI_Buffer_attach( buffer, size );
MPI_Bsend( ..., count=20, datatype=type1, ... );
...
MPI_Bsend( ..., count=40, datatype=type2, ... );
the value of size in the MPI_Buffer_attach call should be greater than
the value computed by
MPI_Pack_size( 20, type1, comm, &s1 );
MPI_Pack_size( 40, type2, comm, &s2 );
size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;
The MPI_BSEND_OVERHEAD gives the maximum amount of space that may be used in
the buffer for use by the BSEND routines in using the buffer. This value
is in mpi.h (for C) and mpif.h (for Fortran).
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_detach.
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.
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 guarentee 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_BUFFER
- Invalid buffer pointer. Usually a null buffer where
one is not valid.
- MPI_ERR_INTERN
- An internal error has been detected. This is fatal.
Please send a bug report to mpi-bugs@mcs.anl.gov.
See Also
MPI_Buffer_detach, MPI_Bsend
Location:bufattach.c