Time-Triggered Program Self-Monitoring

Runtime monitoring aims at analyzing the well-being of a system at run time in order to detect errors and steer the system towards a healthy behavior. Such monitoring is a complementary technique to other approaches for ensuring correctness, such as formal verification and testing. In time-triggered runtime monitoring, a monitor runs as a separate process in parallel with an application program under scrutiny and samples the program's state periodically to evaluate a set of properties. Applying this technique in a computing system results in obtaining bounded and predictable overhead. Gaining such characteristics for overhead is highly desirable for designing and engineering time-critical applications, such as safety-critical embedded systems. However, a time-triggered monitor requires certain synchronization features at operating system level and may suffer from various concurrency and synchronization dependencies and overheads as well as possible unreliability of synchronization primitives in a real-time setting. In this paper, we propose a new method, where the program under inspection is instrumented, so that it self-samples its state in a periodic fashion without requiring assistance from an external monitor or internal timer. We call this technique time-triggered self-monitoring. First, we formulate an optimization problem for minimizing the number of points in a program, where self-sampling instrumentation instructions must be inserted. We show that this problem is NP-complete. Consequently, we propose a SAT-based solution and a heuristic to cope with the exponential complexity. Our experimental results show that a time-triggered self-monitored program performs significantly better than the same program monitored by an external time-triggered monitor.