Research On Fault-Tolerance Mechanism Of Service Composition In Pervasive Environment

Pervasive computing is changing our lives, making us feel the convenience made by "ubiquitous" services, however, pervasive computing has also brought new challenges. Compared to the previous computing model, pervasive computing has characteristics such as dispersibility, heterogeneity, openness and so on, these characteristics cause that in pervasive environment services are easy to make mistakes, which is the main reason for the failure of service composition, in order to prevent or reduce the impact caused by the failure, fault-tolerant technology emerge as the times require. In pervasive environment fault-tolerant must support the following two basic rules: transparency and scalability. In the traditional OOP method, to achieve fault-tolerant we must explicitly add fault tolerant logic in all core concerns, which destroys the object-oriented encapsulation thought, inevitably lead to scattering or tangling, and affect further development or remodeling. Therefore, separating fault-tolerant concern from functional concerns is the key point to achieve fault-tolerant in pervasive environment. this paper presents an AOP-based software fault-tolerance approach in Pervasive Environment, using AOP as a separation of concerns mean, based on this, we build a distributed fault-tolerant software development framework on OSGi platform.Firstly, based on the analysis of existing fault-tolerance techniques of the pervasive computing environment, we put forward an AOP-based software fault-tolerance approach in pervasive environment, the main use of the AOP is to carry out the separation of concerns, the crosscutting concerns are separated from core concerns to ensure the highly encapsulation of the core modules; we put forward error characterization-based error classification method, focusing on the impact caused by errors rather than the cause of the errors, which makes the new fault-tolerance extension become simple;we refer to and improve the popular object-oriented language exception throwing and catching mechanism, separate the error detecting and error recovery logic, and realizes modularization development; we use change-of-rate-based executable assertions to check the validity of sensor data , recover the error, improve service reliability, reduce the failure probability of service composition. This approach has high modularization, is easy to extend and realize.Secondly, based on the above approach, we build a distributed fault-tolerant software development framework, the framework based on OSGi platform and AspectJ. It provides basic fault-tolerance support and efficient fault-tolerance function extension mechanism to the software development under pervasive environment. Software developed by this framework has strong fault-tolerance ability, especially for the service errors in pervasive environment.Finally, We develop a fault-tolerance system using the above proposed distributed fault-tolerant software development framework, and we use error injection way to test the fault-tolerance ability of the system. The experimental results show that, the system has strong fault-tolerance ability, which proves that our proposed AOP-based software fault-tolerance approach in pervasive environment is effective, Software developed by the distributed fault-tolerant software development framework has strong fault-tolerance ability.