On Mechanisms for Deadlock Avoidance in SIP Servlet Containers

Increasingly, VoIP applications are being deployed to multi-threaded SIP servlet containers. Unfortunately, the standard specification for these containers is silent with regard to synchronization issues, and the lack of direction has led different vendors to adopt a variety of different and incompatible policies for preventing data races among concurrent threads. In addition to the obvious portability problems, some policies make servlet code prone to deadlock under common scenarios of use. This paper documents this problem with concrete examples and proposes modifications to the standard to allow programmers to implement the protocols needed to avoid these common deadlocks. These extensions will open the way for automatic generation of the synchronization logic needed to implement these avoidance protocols, thereby increasing the safety and reliability of applications deployed in this environment.