comm - communicator (handle)
out - the new copy of the input communicator (handle).
The MPI_Comm_dup() function is used to duplicate a communicator. The new communicator should eventually be freed with the MPI_Comm_free() function. If the process is not a member of this communicator, then MPI_COMM_NULL is returned in out .
In C++, this function will return the new communicator out , as its return value.
The communicator must be a valid one (not MPI_COMM_NULL). PMPI_Comm_free() is the profiling version of this function.
This function will call the copy function for all attributes attached to the original communicator. Such copy functions may fail, returning something other than MPI_SUCCESS. If so, then this function will fail to construct a new communicator, and return that error code. However, if there are several attributes, then it is possible that a delete function could then fail with some other error code. If that happens, this function will return MPI_ERR_OTHER due to the conflicting error codes.
All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.
In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.
MPI_SUCCESS - No error;
MPI_ERR_PENDING - Pending exception;
MPI_ERR_COMM - Invalid communicator;
MPI_ERR_ARG - Invalid output pointer;
MPI_ERR_OTHER - Conflicting error codes between user copy and delete attribute functions;
MPI_ERR_INTERN - Out of memory. This may be fatal.
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