Functional validation of fault-tolerant asynchronous algorithms

The paper presents an alternative approach to the formal specification and validation of distributed asynchronous algorithms. It begins with a syntactically correct description of the algorithm whose correctness is then to be validated. The validation of the algorithm is based on the process-oriented discrete simulation and permits a partial correctness validation of the algorithm implemented by a program. The suggested method enables to model independent activity of several processors (using pseudo-parallel processes) in simulation time and to model communication channels with defined time behavior and failure semantics. Using the approach it is easy to add other processes like model of system´s environment, fault injector and state observer. The method is described with the aid of a simple C-based validation tool called C-Sim. The utilization of C-Sim requires only slight changes in C-coded implementation of the verified algorithm. An example of validation of distributed election algorithm with the presence of faults is presented.