SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Buffer_attach(void *buf, int size)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'

          MPI_BUFFER_ATTACH(BUF, SIZE, IERROR)
              <type>  BUF(*)
              INTEGER SIZE, IERROR

   Fortran 2008 Syntax
          USE mpi_f08

          MPI_Buffer_attach(buffer, size, ierror)
              TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buffer
              INTEGER, INTENT(IN) :: size
              INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • buf : Initial buffer address (choice).

       • size : Buffer size, in bytes (integer).

OUTPUT PARAMETER

       • ierror : Fortran only: Error status (integer).

DESCRIPTION

       Provides  to  MPI a buffer in the user’s memory to be used for buffering outgoing messages. The buffer is
       used only by messages sent in buffered mode. Only one buffer can be attached to a process at a time.

NOTES

       The size given should be the sum of the sizes of all outstanding Bsends that you  intend  to  have,  plus
       MPI_BSEND_OVERHEAD bytes 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( buf, 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;

       MPI_BSEND_OVERHEAD  gives the maximum amount of buffer space that may be used by the Bsend routines. This
       value is in mpi.h for C and mpif.h for Fortran.

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.

       SEE ALSO:

          • MPI_Buffer_detach

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       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                              MPI_BUFFER_ATTACH(3)