Reversing Parallel Programs with Blocks and Procedures

Abstract

We show how to reverse a while language extended with blocks, local variables, procedures and the interleaving parallel composition. Annotation is defined along with a set of operational semantics capable of storing necessary reversal information, and identifiers are introduced to capture the interleaving order of an execution. Inversion is defined with a set of operational semantics that use saved information to undo an execution. We prove that annotation does not alter the behaviour of the original program, and that inversion correctly restores the initial program state.

Software and Reversible Systems: A Survey of Recent Activities

“…Hoey and Ulidowski introduce a small imperative while language and describe a state-saving approach to reversing executions [33]. This was then extended to support an imperative concurrent language, using identifiers to capture the specific interleaving order and to ensure statements are reversed in the correct order [34]. The proof of correctness provided shows that the reversal is both correct and garbage free.…”

“…The syntax of this language follows. The program state is represented as a series of environments, including the variable environment γ (linking variables to memory locations), the data store σ (linking memory locations to values), the procedure environment μ (storing multiple copies of procedure bodies being executed in parallel) and the while environment β (storing multiple copies of loops being executed in parallel) [34].…”

“…The execution of an annotated program is defined in terms of small step operational semantics, where each rule performs the expected forwards execution alongside the saving of reversal information and assigning of an identifier [34].…”

“…This approach is proved to perform correct reversal information saving as well as correct and garbage-free inversion. The two results are described in [34] and extended to hold for all programs including parallel composition in [30]. The first, named the annotation result, states that an original program and its annotated version executed on the same initial program state will produce equivalent final program states, with the obvious exception of the annotated execution populating the auxiliary store with the required reversal information.…”

Reversing P/T Nets

“…Reversible computing is attracting interest for its applications in many fields including hardware design and quantum computing [27], the modelling of biochemical reactions [23,11,24], parallel discrete event simulation [25] and program reversing for debugging [7,14,10].…”