Fast, Flexible, Polyglot Instrumentation Support for Debuggers and other Tools

Software development tools that interact with running programs, for instance debuggers, are presumed to demand difficult tradeoffs among performance, functionality, implementation complexity, and user convenience. A fundamental change in thinking obsoletes that presumption and enables the delivery of effective tools as a forethought, no longer an afterthought. We have extended the open source multi-language \platform{} with a language-agnostic Instrumentation Framework, including (1) low-level, extremely low-overhead execution event interposition, built directly into the high-performance runtime; (2) shared language-agnostic instrumentation services, requiring minimal per-language specialization; and (3) versatile APIs for constructing many kinds of client tools without modifying the VM. A new design uses this framework to implement debugging services for arbitrary languages (possibly in combination) with little effort from language implementor. We show that, when optimized, the service has no measurable overhead and generalizes to other kinds of tools. It is now possible for a client in a production environment, with thread safety, to dynamically insert into an executing program an instrumentation probe that incurs near zero performance cost until actually used to access (or modify) execution state. Other applications include tracing and stepping required by some languages, as well as platform requirements such as the need to timebox script executions. Finally, opening public API access to runtime state encourages advanced tool development and experimentation with much reduced effort.