A Concurrency and Time Centered Framework for Certification of Autonomous Space Systems
Future space missions, such as Mars Science Laboratory, suggest the engineering of some of the most complex man-rated autonomous software systems. The present process-oriented certification methodologies are becoming prohibitively expensive and do not reach the level of detail of providing guidelines for the development and validation of concurrent software. Time and concurrency are the most critical notions in an autonomous space system. In this work we present the design and implementation of the first concurrency and time centered framework for product-oriented software certification of autonomous space systems. To achieve fast and reliable concurrent interactions, we define and apply the notion of Semantically Enhanced Containers (SEC). SECs are data structures that are designed to provide the flexibility and usability of the popular ISO C++ STL containers, while at the same time they are hand-crafted to guarantee domain-specific policies, such as conformance to a given concurrency model. The application of nonblocking programming techniques is critical to the implementation of our SEC containers. Lock-free algorithms help avoid the hazards of deadlock, livelock, and priority inversion, and at the same time deliver fast and scalable performance. Practical lock-free algorithms are notoriously difficult to design and implement and pose a number of hard problems such as ABA avoidance, high complexity, portability, and meeting the linearizability correctness requirements. This dissertation presents the design of the first lock-free dynamically resizable array. Our approach o ers a set of practical, portable, lock-free, and linearizable STL vector operations and a fast and space effcient implementation when compared to the alternative lock- and STM-based techniques. Currently, the literature does not offer an explicit analysis of the ABA problem, its relation to the most commonly applied nonblocking programming techniques, and the possibilities for its detection and avoidance. Eliminating the hazards of ABA is left to the ingenuity of the software designer. We present a generic and practical solution to the fundamental ABA problem for lock-free descriptor-based designs. To enable our SEC container with the property of validating domain-specific invariants, we present Basic Query, our expression template-based library for statically extracting semantic information from C++ source code. The use of static analysis allows for a far more efficient implementation of our nonblocking containers than would have been otherwise possible when relying on the traditional run-time based techniques. Shared data in a real-time cyber-physical system can often be polymorphic (as is the case with a number of components part of the Mission Data System's Data Management Services). The use of dynamic cast is important in the design of autonomous real-time systems since the operation allows for a direct representation of the management and behavior of polymorphic data. To allow for the application of dynamic cast in mission critical code, we validate and improve a methodology for constant-time dynamic cast that shifts the complexity of the operation to the compiler's static checker. In a case study that demonstrates the applicability of the programming and validation techniques of our certification framework, we show the process of verification and semantic parallelization of the Mission Data System's (MDS) Goal Networks. MDS provides an experimental platform for testing and development of autonomous real-time flight applications.