Open MPI logo

MPI_Bsend(3) man page (version 5.0.0rc2)

  |   Home   |   Support   |   FAQ   |  

« Return to documentation listing

Table of Contents

Name

C]MPI_BsendR] - Basic send with user-specified buffering.

Syntax

C Syntax



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



C]USE MPI! or the older form: INCLUDE [aq]mpif.h[aq]MPI_BSEND(BUF, COUNT,DATATYPE, DEST, TAG, COMM, IERROR) <type> BUF(*) INTEGER COUNT, DATATYPE, DEST, TAG, COMM, IERRORR]Fortran 2008 Syntax



C]USE mpi_f08MPI_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) :: ierrorR]Input Parameters

[bu]
C]bufR] : Initial address of send buffer (choice).
[bu]
C]countR] : Number of entries in send buffer (nonnegative integer).
[bu]
C]datatypeR] : Datatype of each send buffer element (handle).
[bu]
C]destR] : Rank of destination (integer).
[bu]
C]tagR] : Message tag (integer).
[bu]
C]commR] : Communicator (handle).

Output Parameters

[bu]
C]IERRORR] : Fortran only: Error status (integer).

Description

C]MPI_BsendR] 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 C]MPI_Buffer_attachR]).

In deciding how much buffer space to allocate, remember that the buffer space is not available for reuse by subsequent C]MPI_BsendR]s 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:


C]MPI_Buffer_attach( b, n*sizeof(double) + MPI_BSEND_OVERHEAD );for (i=0; i<m; i++) { MPI_Bsend( buf, n, MPI_DOUBLE, ... );}R]because only enough buffer space is provided for a single send, and the
loop may start a second C]MPI_BsendR] before the first is done making use of the buffer.

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

Errors

Almost all MPI routines return an error value; C routines as the value; C routines as the value of the function and Fortran routines in the last argument.

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 C]MPI_Comm_set_errhandlerR]; the predefined error handler C]MPI_ERRORS_RETURNR] 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.


Table of Contents

« Return to documentation listing