MPI_Barrier(3)                        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.


ALGORITHM
       If the underlying device cannot do better, a tree-like or combine algo-
       rithm is used to  broadcast a message to all members of the  communica-
       tor.   We  can  modify  this  to  use  "blocks"  at  a later time  (see
       MPI_Bcast ).


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
       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.  Before the value is returned, the current MPI error
       handler is called.  By default, this error handler aborts the MPI  job.
       The  error  handler may be changed with MPI_Errhandler_set ; the prede-
       fined 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.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_COMM
              - Invalid communicator.  A common error is to use a null  commu-
              nicator in a call (not even allowed in MPI_Comm_rank ).

LOCATION
       barrier.c



                                  11/14/2001                    MPI_Barrier(3)