Return all the run names in the `EventMultiplexer`.

    Returns:
    ```
      {runName: { scalarValues: [tagA, tagB, tagC],
                  graph: true, meta_graph: true}}
    ```

def Runs(self):
    """Return all the run names in the `EventMultiplexer`.

    Returns:
    ```
      {runName: { scalarValues: [tagA, tagB, tagC],
                  graph: true, meta_graph: true}}
    ```
    """
    with self._accumulators_mutex:
      # To avoid nested locks, we construct a copy of the run-accumulator map
      items = list(six.iteritems(self._accumulators))
    return {run_name: accumulator.Tags() for run_name, accumulator in items}