def bw_usage_update_at_top(self, message, bw_update_info, **kwargs):
        if not self._at_the_top():
            return
        self.db.bw_usage_update(message.ctxt, **bw_update_info)
Signal handler for graceful shutdown.
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/cells/messaging.py/_BroadcastMessageMethods.bw_usage_update_at_top--crossover with--dataset/ETHPy150Open AppScale/appscale/Hermes/hermes.py/signal_handler