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MPI_Comm_dup
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Duplicates an existing communicator with all its cached information
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Synopsis
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int MPI_Comm_dup(MPI_Comm comm, MPI_Comm * newcomm)
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Input Parameters
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comm Communicator to be duplicated (handle)
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Output Parameters
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newcomm A new communicator over the same group as <tt>comm</tt> but with a new
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context. See notes. (handle)
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Notes
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This routine is used to create a new communicator that has a new
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communication context but contains the same group of processes as
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the input communicator. Since all MPI communication is performed
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within a communicator (specifies as the group of processes plus
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the context), this routine provides an effective way to create a
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private communicator for use by a software module or library. In
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particular, no library routine should use <tt>MPI_COMM_WORLD</tt> as the
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communicator; instead, a duplicate of a user-specified communicator
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should always be used. For more information, see Using MPI, 2nd
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edition.
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Because this routine essentially produces a copy of a communicator,
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it also copies any attributes that have been defined on the input
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communicator, using the attribute copy function specified by the
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<tt>copy_function</tt> argument to <tt>MPI_Keyval_create</tt>. This is
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particularly useful for (a) attributes that describe some property
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of the group associated with the communicator, such as its
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interconnection topology and (b) communicators that are given back
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to the user; the attibutes in this case can track subsequent
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<tt>MPI_Comm_dup</tt> operations on this communicator.
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Thread and Interrupt Safety
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This routine is thread-safe. This means that this routine may be
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safely used by multiple threads without the need for any user-provided
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thread locks. However, the routine is not interrupt safe. Typically,
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this is due to the use of memory allocation routines such as <tt>malloc
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</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
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Notes for Fortran
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All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
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an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
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</tt>is an integer and has the same meaning as the return value of the routine
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in C. In Fortran, MPI routines are subroutines, and are invoked with the
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<tt>call</tt> statement.
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All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
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</tt>in Fortran.
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Errors
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All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
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C routines as the value of the function and Fortran routines in the last
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argument. Before the value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job. The error handler
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may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
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<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
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RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
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its use is deprecated. The predefined error handler
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<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
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Note that MPI does not guarentee that an MPI program can continue past
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an error; however, MPI implementations will attempt to continue whenever
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possible.
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MPI_SUCCESS No error; MPI routine completed successfully.
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MPI_ERR_COMM Invalid communicator. A common error is to use a null
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communicator in a call (not even allowed in <tt>MPI_Comm_rank</tt>).
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See Also
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MPI_Comm_free, MPI_Keyval_create, MPI_Attr_put, MPI_Attr_delete,
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MPI_Comm_create_keyval, MPI_Comm_set_attr, MPI_Comm_delete_attr
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