ng state
(future calls to running() will return True) and True is returned.

This method should be called by Executor implementations before
executing the work associated with this future. If this method returns
False then the work should not be executed.

Returns:
    False if the Future was cancelled, True otherwise.

Raises:
    RuntimeError: if this method was already called or if set_result()
        or set_exception() was called.
NFTz!Future %s in unexpected state: %sz