mpi_buffer_detach(3openmpi) [osx man page]

MPI_Buffer_detach(3OpenMPI)											       MPI_Buffer_detach(3OpenMPI)

NAME

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

SYNTAX

C Syntax
       #include <mpi.h>
       int MPI_Buffer_detach(void *buf, int *size)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_BUFFER_DETACH(BUF, SIZE, IERROR)
	    <type>    BUF(*)
	    INTEGER   SIZE, IERROR

C++ Syntax
       #include <mpi.h>
       int Detach_buffer(void*& buffer)

OUTPUT PARAMETERS

       buf	 Initial buffer address (choice).

       size	 Buffer size, in bytes (integer).

       IERROR	 Fortran only: Error status (integer).

DESCRIPTION

       Detach  the  buffer  currently  associated  with MPI. The call returns the address and the size of the detached buffer. This operation will
       block until all messages currently in the buffer have been transmitted. Upon return of this function, the user may reuse or deallocate  the
       space taken by the buffer.

       Example: Calls to attach and detach buffers.

	   #define BUFFSIZE 10000
	   int size
	   char *buff;
	   MPI_Buffer_attach( malloc(BUFFSIZE), BUFFSIZE);
	   /* a buffer of 10000 bytes can now be used by MPI_Bsend */
	   MPI_Buffer_detach( &buff, &size);
	   /* Buffer size reduced to zero */
	   MPI_Buffer_attach( buff, size);
	   /* Buffer of 10000 bytes available again */

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's simple) and weaknesses (it only works  for  nested
       usages).

       For  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.

       For C: Even though the buf argument is declared as void, it is really the address of  a	void  pointer.	See  Rationale,  below,  for  more
       details.

       Even though the C functions MPI_Buffer_attach and MPI_Buffer_detach both have a first argument of type void*, these arguments are used dif-
       ferently: A pointer to the buffer is passed to MPI_Buffer_attach; the address of the pointer is passed to MPI_Buffer_detach, so	that  this
       call can return the pointer value.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func-
       tions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception  mechanism
       will be used to throw an MPI:Exception object.

       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 MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN  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.

SEE ALSO

       MPI_Buffer_attach
       MPI_Bsend

Open MPI 1.2							  September 2006				       MPI_Buffer_detach(3OpenMPI)

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)