Global types with internal delegation

Abstract

This paper investigates a new form of delegation for multiparty session calculi. Usually, delegation allows a session participant to appoint a participant in another session to act on her behalf. This means that delegation is inherently an inter-session mechanism, which requires session interleaving. Hence delegation falls outside the descriptive power of global types, which specify single sessions. As a consequence, properties such as deadlock-freedom or lock-freedom are difficult to ensure in the presence of delegation. Here we adopt a different view of delegation, by allowing participants to delegate tasks to each other within the same multiparty session. This way, delegation occurs within a single session (internal delegation) and may be captured by its global type. To increase flexibility in the use of delegation, our calculus uses connecting communications, which allow optional participants in the branches of choices. By these means, we are able to express conditional delegation. We present a session type system based on global types with internal delegation, and show that it ensures the usual safety properties of multiparty sessions, together with a progress property.

Prioritise the Best Variation

“…They synthesise safe and deadlock-free global types from local types leveraging LTSs and communicating automata. Castellani et al [16] guarantee lock freedom, a stronger property than deadlock freedom, for MPST with internal delegation, where participants in the same session are allowed to delegate tasks to each other, and internal delegation is captured by the global type. Scalas and Yoshida [46] provide a revision of the foundations for MPST, and offer a less complicated and more general theory, by removing duality/consistency.…”

Asynchronous Sessions with Input Races

“…Rule [IN] requires that the global type and the process read the same messages on the queue. To this end, it uses the index set of ready messages defined in Definition 3.5, collecting the indices of the live branches of the global type and of the input process 5 , and asking them to be equal (condition rm({ q i , ℓ i , p } i∈I , M ) = rm({ q h , ℓ h , p } h∈H , M ). This set of indices must not be empty (condition J = / 0).…”

“…Although these were useful simplifying assumptions in order to achieve multiparty session correctness, they limited the expressiveness of global types, ruling out relevant protocols. For this reason, more permissive choice constructors were investigated in subsequent work [1,2,9,16,13,3,5,14,10,17]. A widely adopted relaxation of the choice operator, originally proposed in [1], allows third participants to behave differently in different branches, provided they are notified of which branch has been chosen.…”

“…Recent proposals introduce more flexibility in input choices for processes [3,5,14,10,17]. The work [10] defines the property of race-freedom for sessions as the absence, at any stage of computation, of a branching between communications from different senders towards the same receiver leading to distinct target states.…”

Event Structure Semantics for Multiparty Sessions

“…We also plan to investigate the extension of our asynchronous calculus with delegation. While delegation is usually defined in session calculi with channels, and modelled using the channel passing mechanism of the π-calculus, an alternative notion of delegation for a session calculus without channels, called "internal delegation", was proposed in [CDGH20]. Hence, one possibility would be to investigate internal delegation in our asynchronous calculus without channels; another option would be to depart from our present calculus, admittedly very simple, and investigate the classical notion of delegation in an asynchronous calculus with channels.…”