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MPI_Comm_dup(3)                       MPI                      MPI_Comm_dup(3)


NAME

       MPI_Comm_dup -  Duplicates an existing communicator with all its cached
       information


SYNOPSIS

       int MPI_Comm_dup(MPI_Comm comm, MPI_Comm *newcomm)


INPUT PARAMETER

       comm   - Communicator to be duplicated (handle)


OUTPUT PARAMETER

       newcomm
              - A new communicator over the same group as comm but with a new
              context. See notes.  (handle)


NOTES

       This routine is used to create a new communicator that has a new
       communication context but contains the same group of processes as the
       input communicator.  Since all MPI communication is performed within a
       communicator (specifies as the group of processes plus the context),
       this routine provides an effective way to create a private communicator
       for use by a software module or library.  In particular, no library
       routine should use MPI_COMM_WORLD as the communicator; instead, a
       duplicate of a user-specified communicator should always be used.  For
       more information, see Using MPI, 2nd edition.

       Because this routine essentially produces a copy of a communicator, it
       also copies any attributes that have been defined on the input
       communicator, using the attribute copy function specified by the
       copy_function argument to MPI_Keyval_create .  This is particularly
       useful for (a) attributes that describe some property of the group
       associated with the communicator, such as its interconnection topology
       and (b) communicators that are given back to the user; the attibutes in
       this case can track subsequent MPI_Comm_dup operations on this
       communicator.


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.


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_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.

       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 ).


SEE ALSO

       MPI_Comm_free, MPI_Keyval_create, MPI_Attr_put, MPI_Attr_delete,
       MPI_Comm_create_keyval, MPI_Comm_set_attr, MPI_Comm_delete_attr


LOCATION

       src/mpi/comm/comm_dup.c

                                   9/20/2012                   MPI_Comm_dup(3)

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