code: void registerTaskEnded(Task task) {
          synchronized (m_activeTasks) {
              String mapKey = createMapKey(task.getTenant(), task.getTaskID());
              if (m_activeTasks.remove(mapKey) == null) {
                  m_logger.warn("Task {} registered as ended but was not running", mapKey);
              }
          }
      }
docs: Called by a Task when it's thread finishes. This lets the task manager know
  that another slot has opened-up.
  
  @param task   {@link Task} that just finished.