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.TH MPI_Comm_dup 3 "11/12/2019" " " "MPI"
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.SH NAME
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MPI_Comm_dup \- Duplicates an existing communicator with all its cached information
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.SH SYNOPSIS
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.nf
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int MPI_Comm_dup(MPI_Comm comm, MPI_Comm * newcomm)
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.fi
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.SH INPUT PARAMETERS
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.PD 0
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.TP
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.B comm
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- Communicator to be duplicated (handle)
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.PD 1
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.SH OUTPUT PARAMETERS
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.PD 0
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.TP
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.B newcomm
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- A new communicator over the same group as
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.I comm
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but with a new
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context. See notes. (handle)
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.PD 1
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.SH 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
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.B 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
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.I MPI_COMM_WORLD
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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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.I copy_function
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argument to
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.I MPI_Keyval_create
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\&.
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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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.I MPI_Comm_dup
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operations on this communicator.
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.SH 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
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.I malloc
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or other non-MPICH runtime routines that are themselves not interrupt-safe.
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.SH NOTES FOR FORTRAN
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All MPI routines in Fortran (except for
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.I MPI_WTIME
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and
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.I MPI_WTICK
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) have
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an additional argument
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.I ierr
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at the end of the argument list.
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.I ierr
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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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.I call
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statement.
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All MPI objects (e.g.,
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.I MPI_Datatype
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,
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.I MPI_Comm
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) are of type
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.I INTEGER
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in Fortran.
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.SH ERRORS
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All MPI routines (except
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.I MPI_Wtime
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and
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.I MPI_Wtick
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) 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
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.I MPI_Comm_set_errhandler
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(for communicators),
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.I MPI_File_set_errhandler
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(for files), and
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.I MPI_Win_set_errhandler
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(for
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RMA windows). The MPI-1 routine
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.I MPI_Errhandler_set
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may be used but
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its use is deprecated. The predefined error handler
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.I MPI_ERRORS_RETURN
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may be used to cause error values to be returned.
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Note that MPI does
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.B not
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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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.PD 0
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.TP
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.B MPI_SUCCESS
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- No error; MPI routine completed successfully.
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.PD 1
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.PD 0
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.TP
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.B MPI_ERR_COMM
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- Invalid communicator. A common error is to use a null
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communicator in a call (not even allowed in
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.I MPI_Comm_rank
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).
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.PD 1
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.SH SEE ALSO
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MPI_Comm_free, MPI_Keyval_create, MPI_Attr_put, MPI_Attr_delete,
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.br
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MPI_Comm_create_keyval, MPI_Comm_set_attr, MPI_Comm_delete_attr
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