Malte Schmitz

Runtime verification deals with checking correctness properties on the runs of a system under scrutiny. To achieve this, it addresses a variety of sub-problems related to monitoring of systems: These range from the appropriate design of a specification language over efficient monitor generation as hardware and software monitors to solutions for instrumenting the monitored system, preferably in a non-intrusive way. Further aspects play a role for the usability of a runtime verification toolchain, e.g. availability, sufficient documentation and the existence of a developer community. In this paper we present the TeSSLa ecosystem, a runtime verification framework built around the stream runtime verification language TeSSLa: It provides a rich toolchain of mostly freely available compilers for monitor generation on different hardware and software backends, as well as instrumentation mechanisms for various runtime verification requirements. Additionally, we highlight how the online resources and supporting tools of the community-driven project enable the productive usage of stream runtime verification.

Runtime Verification (RV) studies how to analyze execution traces of a system under observation. Stream Runtime Verification (SRV) applies stream transformations to obtain information from observed traces. Incomplete traces with information missing in gaps pose a common challenge when applying RV and SRV techniques to real-world systems as RV approaches typically require the complete trace without missing parts. This paper presents a solution to perform SRV on incomplete traces based on abstraction. We use TeSSLa as specification language for non-synchronized timed event streams and define abstract event streams representing the set of all possible traces that could have occurred during gaps in the input trace. We show how to translate a TeSSLa specification to its abstract counterpart that can propagate gaps through the transformation of the input streams and thus generate sound outputs even if the input streams contain gaps and events with imprecise values. The solution has been implemented as a set of macros for the original TeSSLa and an empirical evaluation shows the feasibility of the approach.

We present TeSSLa, a specification language based on stream runtime verification, designed for monitoring a specific class of realtime signals. Our monitors can observe concurrent systems with a shared clock, but where each component reports observations as signals that arrive to the monitor at different speeds and with different and varying latencies. The signals and streams that TeSSLa supports (including inputs and final verdicts) are not restricted to be Booleans but can be data from richer domains, including integers and reals with arithmetic operations and aggregations. Consequently, TeSSLa can be used both for checking logical properties, and for computing statistics and general numeric temporal metrics (and properties on these richer metrics). We present an online evaluation algorithm for TeSSLa specifications and show a formal proof of the correctness of concurrent implementations of the evaluation algorithm. Finally, we report an empirical evaluation of a highly concurrent Erlang implementation of the monitoring algorithm.