Stateful breakpoints: a practical approach to defining parameterized runtime monitors

Abstract

A runtime monitor checks a safety property during a program's execution. A parameterized runtime monitor can monitor properties containing free variables, or parameters. For instance, a monitor for the regular expression "close(s)+ read(s)" will warn the user when reading from a stream s that has previously been closed. Parameterized runtime monitors are very expressive, and research on this topic has lately gained much traction in the Runtime Verification community. Existing monitoring algorithms are very efficient. Nevertheless, existing tools provide little support for actually defining runtime monitors, probably one reason for why few practitioners are using runtime monitoring so far. In this work we propose the idea of allowing programmers to express parameterized runtime monitors through stateful breakpoints, temporal combinations of normal breakpoints, a concept well known to programmers. We show how we envision programmers to define runtime monitors through stateful breakpoints and parameter bindings through breakpoint expressions. Further, we explain how stateful break- points improve the debugging experience: they are more expressive than normal breakpoints, nevertheless can be evaluated more efficiently. Stateful breakpoints can be attached to bug reports for easy reproducibility: they often allow developers to run directly to the bug in one single step. Further, stateful breakpoints can potentially be inferred from a running debugging session or using property inference and fault localization tools.