Correspondence assertions for process synchronization in concurrent communications

Abstract

High-level specification of patterns of communications such as protocols can be modeled elegantly by means of session types [14]. However, a number of examples suggest that session types fall short when finer precision on protocol specification is required. In order to increase the expressiveness of session types we appeal to the theory of correspondence assertions [5,10]. The resulting type discipline augments the types of long term channels with effects and thus yields types which may depend on messages read or written earlier within the same session. We prove that evaluation preserves typability and that well-typed processes are safe. Also, we illustrate how the resulting theory allows us to address the shortcomings present in the pure theory of session types.

A Distributed Object-Oriented Language with Session Types

“…Thus, the type system can statically check the consistent composition of communication protocols. The soundness of our system is weaker than that of all systems of session types for π-calculus processes [4,5,13,15,17,25]. In fact all these systems assure a perfect pairing between processes willing to communicate.…”

“…1. It is an extension of FJ [18], MJ [3] and DJ [1] (while omitting the new distributed primitives introduced in [1]), augmented with primitives for session communication [5,15,17,27]. The metavariable t ranges over types for channels and expressions, C ranges over class names, s ranges over session types.…”

“…5 Neither are request u s {E}, accept u s {E}, u .sendIf (e ){E}{e}, u .sendIf (e ){e }{E}, u .sendWhile (e ){E}, u .receiveIf {E}{e}, u .receiveIf {e }{E}, or u .receiveWhile{E} evaluation contexts, because they would allow session bodies to run before the start of the session, or parts of a conditional or iterative session to run before determining which conditional branch should be selected, or whether the iteration should continue.…”

“…for π-calculus-based formalisms [4,5,13,15,17,25], for CORBA [26], for a λ-calculus with side-effects [14], for a multi-threaded functional language [27], and recently, for a W3C standard description language for web services called Choreography Description Language (CDL) [29]. To our knowledge, the integration of session types into an object-oriented language (even a small, core calculus, as in [3,10,18]) has not been attempted so far.…”

“…To focus on the introduction of session types, L doos does not include language features such as exceptions [2], synchronisation, serialisation [1], class (down)loading [1,11], code or agent mobility [1,7,28], polymorphism [6,18,27], recursive types [26] or correspondence assertions [4,5]. We believe that the inclusion of such features into L doos is possible, albeit not necessarily trivial.…”