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RedHat 9 (Linux i386) - man page for mpi_barrier (redhat section 3)

MPI_Barrier(3)				     LAM/MPI				   MPI_Barrier(3)

NAME
       MPI_Barrier -  Blocks until all process have reached this routine.

SYNOPSIS
       #include <mpi.h>
       int MPI_Barrier(MPI_Comm comm)

INPUT PARAMETERS
       comm   - communicator (handle)

NOTES
       Blocks  the caller until all group members have called it; the call returns at any process
       only after all group members have entered the call.

USAGE WITH IMPI EXTENSIONS
       This function has had the IMPI extensions implemented.  It is legal to call this  function
       on IMPI communicators.

ALGORITHM
       For  4 or less ranks, a linear algorithm is used, where rank 0 first receives synchroniza-
       tion message from each other rank.  Rank 0 then sends out  a  synchronization  message  to
       each other rank.

       If more than 4 ranks are involved, a tree-based algorithm is used to receive and then send
       the synchronization messages to and from rank 0.

NOTES FOR FORTRAN
       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argu-
       ment 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 excep-
       tions 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_COMM
	      - Invalid communicator.  A common error is to use a null	communicator  in  a  call
	      (not even allowed in MPI_Comm_rank ).
       MPI_ERR_COMM
	      -  Invalid  communicator.   LAM/MPI  does  not  yet support invoking collectives on
	      intercommunicators.

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/sowing/sowing.tar.gz ), the initial for-
       matting, and some initial text for most of the MPI-1 man pages.

LOCATION
       barrier.c

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


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