A Generic Approach to Monitor Program Executions

Monitoring requires to gather data about executions. The monitoring func-tionalities currently available are built on top of ad hoc instrumentations. Most of them are implemented at low-level; in any case they require an in-depth knowledge of the system to instrument. The best people to implement these instrumentations are generally the implementors of the compiler. They, however, cannot decide which data to gather. Indeed, hundreds of variants can be useful and only end-users know what they want. In this article, we propose a primitive which enables users to easily specify what to monitor. It is built on top of the tracer of the Mercury compiler. We illustrate how to use this primitive on two diierent kinds of monitoring. Firstly, we implement monitors that collect various kinds of statistics; each of them is well-known, the novelty is that users can get exactly the variants they need. Secondly, we deene two notions of test coverage for logic programs and show how to measure coverage rates with our primitive. To our knowledge no deenition of test coverage exist for logic programming so far. Each example is only a few lines of Mercury. Measurements show that the performance of the primitive on the above examples is acceptable for an execution of several millions of trace events. Our primitive, although simple, lays the foundation for a generic and powerful monitoring environment.