oracular (3) MPI_Bsend.openmpi.3.gz

NAME

       MPI_Bsend - Basic send with user-specified buffering.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Bsend(const void *buf, int count, MPI_Datatype datatype,
            int dest, int tag, MPI_Comm comm)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_BSEND(BUF, COUNT,DATATYPE, DEST, TAG, COMM, IERROR)
            <type>    BUF(*)
            INTEGER   COUNT, DATATYPE, DEST, TAG, COMM, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Bsend(buf, count, datatype, dest, tag, comm, ierror)
            TYPE(*), DIMENSION(..), INTENT(IN) :: buf
            INTEGER, INTENT(IN) :: count, dest, tag
            TYPE(MPI_Datatype), INTENT(IN) :: datatype
            TYPE(MPI_Comm), INTENT(IN) :: comm
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       void Comm::Bsend(const void* buf, int count, const
            Datatype& datatype, int dest, int tag) const

INPUT PARAMETERS

       buf       Initial address of send buffer (choice).

       count     Number of entries in send buffer (nonnegative integer).

       datatype  Datatype of each send buffer element (handle).

       dest      Rank of destination (integer).

       tag       Message tag (integer).

       comm      Communicator (handle).

OUTPUT PARAMETER

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_Bsend performs a buffered-mode, blocking send.

NOTES

       This  send  is  provided  as a convenience function; it allows the user to send messages without worrying
       about where they are buffered (because the user must have provided buffer space with MPI_Buffer_attach).

       In deciding how much buffer space to allocate, remember that the buffer space is not available for  reuse
       by  subsequent  MPI_Bsends  unless  you  are certain that the message has been received (not just that it
       should have been received).  For example, this code does not allocate enough buffer space:

           MPI_Buffer_attach( b, n*sizeof(double) + MPI_BSEND_OVERHEAD );
           for (i=0; i<m; i++) {
               MPI_Bsend( buf, n, MPI_DOUBLE, ... );
           }

       because only enough buffer space is provided for a single send, and the loop may start a second MPI_Bsend
       before the first is done making use of the buffer.

       In  C, you can force the messages to be delivered by MPI_Buffer_detach( &b, &n ); MPI_Buffer_attach( b, n
       ); (The MPI_Buffer_detach will not complete until all buffered messages are delivered.)

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++ functions 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_Ibsend
       MPI_Bsend_init