Notifies the process that it has reached the barrier and returns immediately


int MPI_Ibarrier(MPI_Comm comm, MPI_Request *request)

Input Parameters

communicator (handle)

Output Parameters

communication request (handle)


MPI_Ibarrier is a nonblocking version of MPI_barrier. By calling MPI_Ibarrier, a process notifies that it has reached the barrier. The call returns immediately, independent of whether other processes have called MPI_Ibarrier. The usual barrier semantics are enforced at the corresponding completion operation (test or wait), which in the intra-communicator case will complete only after all other processes in the communicator have called MPI_Ibarrier. In the intercommunicator case, it will complete when all processes in the remote group have called MPI_Ibarrier.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

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.


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_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.