Instant Replay Debugging of Concurrent Logic Programs

One problem with debugging (committed choice) concurrent logic programs is that their behaviour may be non-deterministic, in that successive executions of the same program may produce different results. We describe a scheme, based on the `Instant Replay' scheme developed for more conventional parallel languages, that allows us to reproduce the execution behaviour of a concurrent logic program on subsequent executions, so that the execution may be examined for debugging purposes. The properties of concurrent logic programming languages allow us to simplify our scheme greatly. We have demonstrated our scheme with KLIC, and KL1 on the PIM multiprocessors, but it can also be applied to other committed choice concurrent logic programming languages. 1 Introduction One of the standard ways of debugging a sequential program is to re-execute the program when a bug occurs. This can be done because sequential execution is normally deterministic, so the bug would be reproduced. Moreover, a progra..