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

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 PARAMETERS

       • 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 return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                      MPI_BSEND(3)