OpenFlow is a Software Defined Networking (SDN) protocol that is being deployed in critical network systems. SDN application verification takes an important role in guaranteeing the correctness of the application. Through our investigation, we discover that application verification can be very inefficient under the OpenFlow protocol since there are many race conditions between the data packets and control plane messages. Furthermore, these race conditions also increase the control plane workload and packet forwarding delay. We propose Attendre, an OpenFlow extension, to mitigate the ill effects of the race conditions in OpenFlow networks. We have implemented Attendre in NICE (a model checking verifier), Open vSwitch (a software virtual switch) and NOX (an OpenFlow control platform). Experiments show that Attendre can reduce verification time by several orders of magnitude, and can significantly reduce TCP connection setup time.