Synchronizability for Verification of Asynchronously Communicating Systems

Message-based communication is an increasingly common interaction mechanism used in concurrent and distributed systems where components interact with each other by sending and receiving messages. It is well-known that verification of systems that use asynchronous message-based communication with unbounded FIFO queues is undecidable even when the component behaviors are expressed using finite state machines. In this paper we show that there is a sub-class of such systems, called synchronizable systems, for which certain reachability properties (over send actions and over states with no pending receives) remain unchanged when asynchronous communication is replaced with synchronous communication. Hence, if a system is synchronizable, then the verification of these reachability properties can be done on the synchronous version of the system and the results hold for the asynchronous case. We present a technique for deciding if a given system is synchronizable. Our results are applicable to a variety of domains including verification and analysis of interactions among processes at the OS level, coordination in service-oriented computing and interactions among distributed programs. In this paper we focus on analysis of channel contracts in the Singularity OS. Our experimental results show that almost all channel contracts in the Singularity OS are synchronizable, and, hence, their properties can be analyzed using synchronous communication semantics.