Retractable and Speculative Contracts

Abstract

Abstract. Behavioral contracts are abstract descriptions of the communications that clients and servers perform. Behavioral contracts come naturally equipped with a notion of compliance: when a client and a server follow compliant contracts, their interaction is guaranteed to progress or successfully complete. We study two extensions of contracts, dealing respectively with backtracking and with speculative execution. We show that the two extensions give rise to the same notion of compliance. As a consequence, they also give rise to the same subcontract relation, which determines when one server can be replaced by another preserving compliance. Moreover, compliance and subcontract relation are both decidable in polynomial time.

Session Types for Orchestrated Interactions

“…Such a correspondence does transfer also to session types in a very general sense, as shown in [8]. In our setting, even if a relation of subtyping can be obtained out of a restriction of the subcontract relation defined in [5], the above mentioned correspondence looks unrealistic since, as pointed out in [4], there exists no natural notion of duality 1 for retractable contracts.…”

“…Duality for retractable session contracts can be immediately recovered by extending the formalism of[4] with speculative input choices, as done in[5]. Such extension, however, do not seem to have a clear session-type counterpart 2.…”

A theory of retractable and speculative contracts

“…We discussed in the Introduction the improvements with respect to the previous work presented in [18,17]. Another closely related work is [33,34], where a different form of contracts with rollback is presented.…”

“…As further element supporting this, we show (Section 6) that the backtracking mechanism of retractable contracts can be seen as an application to behavioral contracts of the general theory proposed in [16] to define reversible extensions of process calculi. This paper is an extended and revised version of [17] (a few preliminary results had been originally presented in a workshop paper [18]). Section 6, where the relation between retractable contracts and calculi for reversible computing is investigated, is completely new.…”

Foundations of Reversible Computation

“…In retractable contracts [23,24] the client and the server can both get back to previous decision points and take alternative paths only when the interaction is stuck. The main results in [23,24] are that retractable contracts are a conservative extension of contracts, both compliance and the subcontract relation are decidable in polynomial time, and the dual of a contract always exists and has a simple syntactic characterisation. Furthermore, retractable contracts are equivalent to a novel model of contracts featuring a speculative choice: all the options of the choice are explored concurrently, and the computation succeeds if at least one of the options is successful.…”