Execute the query and get the results. Note that this method can be called by multiple threads, and all will block until
the query execution has completed. Subsequent calls to this method will return the same results.
Cancel the query if it is currently running. Note that this method does not block until the query is cancelled; it merely
marks the query as being cancelled, and the query will terminate at its next available opportunity. Also, subsequent calls
to this method have no affect.
true if the query was executing and will be cancelled, or false if the query was no longer running (because it had
finished successfully or had already been cancelled) and could not be cancelled.