MPI_Barrier
Blocks until all process have reached this routine. 
Synopsis
#include "mpi.h"
int MPI_Barrier ( comm )
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 
membershave entered the call.
Algorithm
If the underlying device cannot do better, a tree-like or 
combinealgorithm is used to broadcast a message wto all members of 
thecommunicator.  We can modifiy 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) 
havean additional argument ierr at the end of the argument list.  
ierris an integer and has the same meaning as the return value of the 
routinein C.  In Fortran, MPI routines are subroutines, and are invoked with 
thecall statement.
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type 
INTEGERin 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 
lastargument.  Before the value is returned, the current MPI error handler 
iscalled.  By default, this error handler aborts the MPI job.  The error 
handlermay be changed with MPI_Errhandler_set; the predefined error 
handlerMPI_ERRORS_RETURN may be used to cause error values to be returned.
Note that MPI does not guarentee that an MPI program can continue 
pastan error.
- 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).
Location:barrier.c