int MPI_Comm_dup(
  MPI_Comm comm,
  MPI_Comm *newcomm
);

Parameters

comm

[in] Communicator to be duplicated (handle)

newcomm

[out] A new communicator over the same group as comm but with a new context. See notes. (handle)

Remarks

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.

Advice to users.

This operation is used to provide a parallel library call with a duplicate communication space that has the same properties as the original communicator. This includes any attributes (see below), and topologies (see chapter Process Topologies ). This call is valid even if there are pending point-to-point communications involving the communicator comm. A typical call might involve a MPI_COMM_DUP at the beginning of the parallel call, and an MPI_COMM_FREE of that duplicated communicator at the end of the call. Other models of communicator management are also possible.

This call applies to both intra- and inter-communicators.

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 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

Example Code

The following sample code illustrates MPI_Comm_dup.