Blocks until all process have reached this routine.


#include "mpi.h"
int MPI_Barrier ( comm )
MPI_Comm comm;

Input Parameters

communicator (handle)


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


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.


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.

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