mpi_buffer_detach(3) [redhat man page]

MPI_Buffer_detach(3)						      LAM/MPI						      MPI_Buffer_detach(3)

NAME

       MPI_Buffer_detach -  Removes an existing buffer (for use in MPI_Bsend etc)

SYNOPSIS

       #include <mpi.h>
       int MPI_Buffer_detach(void *pbuf, int *psize)

OUTPUT PARAMETERS

       pbuf   - initial buffer address (choice)
       psize  - buffer size, in bytes (integer)

NOTES

       The  reason  that  MPI_Buffer_detach  returns the address and size of the buffer being detached is to allow nested libraries to replace and
       restore the buffer.  For example, consider

       int size, mysize, idummy;
       void *ptr, *myptr, *dummy;
       MPI_Buffer_detach(&ptr, &size);
       MPI_Buffer_attach(myptr, mysize);
       // ...library code...
       MPI_Buffer_detach(&dummy, &idummy);
       MPI_Buffer_attach(ptr, size);

       This is much like the action of the Unix signal routine and has the same strengths (it is simple) and weaknesses (it only works for  nested
       usages).

       Note  that  for	this approach to work, MPI_Buffer_detach must return MPI_SUCCESS even when there is no buffer to detach.  In that case, it
       returns a size of zero.	The MPI 1.1 standard for MPI_BUFFER_DETACH contains the text

       The statements made in this section describe the behavior of MPI
       for buffered-mode sends. When no buffer is currently associated,
       MPI behaves as if a zero-sized buffer is associated with the
       process.

       This could be read as applying only to the various Bsend routines.  This implementation takes the position that this  applies  to  MPI_BUF-
       FER_DETACH as well.

NOTES FOR FORTRAN

       All  MPI  routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list.  ierr
       is an integer and has the same meaning as the return value of the routine in C.	In Fortran, MPI routines are subroutines, and are  invoked
       with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

       The  Fortran  binding  for this routine is different.  Because Fortran does not have pointers, it is impossible to provide a way to use the
       output of this routine to exchange buffers.  In this case, only the size field is set.

NOTES FOR C

       Even though the pbuf argument is declared as void * , it is really the address of a void pointer (i.e., void ** ).  See	the  rationale	in
       the MPI Standard for more details.

MORE INFORMATION

       For  more  information,	please	see the official MPI Forum web site, which contains the text of both the MPI-1 and MPI-2 standards.  These
       documents contain detailed information about each MPI function (most of which is not duplicated in these man pages).

       http://www.mpi-forum.org/

ACKNOWLEDGEMENTS

       The LAM Team would like the thank the MPICH Team for the handy program to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow-
       ing/sowing.tar.gz ), the initial formatting, and some initial text for most of the MPI-1 man pages.

LOCATION

       bufdetach.c

LAM
/MPI 6.5.8							    11/10/2002						      MPI_Buffer_detach(3)

MPI_Buffer_attach(3)						      LAM/MPI						      MPI_Buffer_attach(3)

NAME

       MPI_Buffer_attach -  Attaches a user-defined buffer for sending

SYNOPSIS

       #include <mpi.h>
       int MPI_Buffer_attach(void *buf, int size)

INPUT PARAMETERS

       buf    - initial buffer address (choice)
       size   - buffer size, in bytes (integer)

NOTES

       The  size  given  should be the sum of the sizes of all outstanding Bsends that you intend to have, plus a few hundred 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( buffer, 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 space that may be used in the buffer for use by the Bsend  routines  in  using  the  buffer.
       This value is in mpi.h (for C) and mpif.h (for Fortran).

NOTES FOR FORTRAN

       All  MPI  routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list.  ierr
       is an integer and has the same meaning as the return value of the routine in C.	In Fortran, MPI routines are subroutines, and are  invoked
       with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS

       If an error occurs in an MPI function, the current MPI error handler is called to handle it.  By default, this error handler aborts the MPI
       job.  The error handler may be changed with MPI_Errhandler_set ; the predefined error handler MPI_ERRORS_RETURN may be used to cause  error
       values  to  be  returned  (in  C and Fortran; this error handler is less useful in with the C++ MPI bindings.  The predefined error handler
       MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value needs to be recovered).  Note that MPI does not guarantee that an MPI
       program can continue past an error.

       All  MPI  routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the function and Fortran routines in
       the last argument.  The C++ bindings for MPI do not return error values; instead, error values are communicated by throwing  exceptions	of
       type MPI::Exception (but not by default).  Exceptions are only thrown if the error value is not MPI::SUCCESS
	.

       Note  that  if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return upon an error, there will be no way to recover
       what the actual error value was.
       MPI_SUCCESS
	      - No error; MPI routine completed successfully.
       MPI_ERR_BUFFER
	      - Invalid buffer pointer.  Usually a null buffer where one is not valid.
       MPI_ERR_INTERN
	      - An internal error has been detected.  This is fatal.  Please send a bug report	to  the  LAM  mailing  list  (see  http://www.lam-
	      mpi.org/contact.php ).

SEE ALSO

       MPI_Buffer_detach, MPI_Bsend

MORE INFORMATION

       For  more  information,	please	see the official MPI Forum web site, which contains the text of both the MPI-1 and MPI-2 standards.  These
       documents contain detailed information about each MPI function (most of which is not duplicated in these man pages).

       http://www.mpi-forum.org/

ACKNOWLEDGEMENTS

       The LAM Team would like the thank the MPICH Team for the handy program to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow-
       ing/sowing.tar.gz ), the initial formatting, and some initial text for most of the MPI-1 man pages.

LOCATION

       bufattach.c

LAM
/MPI 6.5.8							    11/10/2002						      MPI_Buffer_attach(3)