MPI_BUFFER_ATTACH(3)				     Open MPI				      MPI_BUFFER_ATTACH(3)

MPI_Buffer_attach — Attaches a user-defined buffer for sending.

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 <#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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

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

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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

       See also:

	  • MPI_Buffer_detach <#mpi-buffer-detach>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				      MPI_BUFFER_ATTACH(3)
