Deadlock detection of active objects with synchronous and asynchronous method calls

Open distributed systems are essential in today’s software solutions. However, not all programming paradigms provide natural support for such systems. The setting of concurrent objects is attractive since it supports independent units of computation. In particular we consider concurrent objects communicating by asynchronous method calls supporting nonblocking as well as blocking method calls. In this setting waiting time can be reduced, allowing efficient cooperation between objects. With this concurrency model, deadlock is avoided if blocking calls are avoided. However, blocking calls are sometimes needed to control the order of computation. The non-hierarchical nature of concurrent objects systems gives rise to non-trivial deadlock situations. Deadlocks may occur if there is a call chain with at least one blocking call.We propose a method for static detection of deadlocks, and demonstrate its use on a non-trivial example.