Parameterized Concurrent Multi-Party Session Types

Session types have been proposed as a means of statically verifying implementations of communication protocols. Although prior work has been successful in verifying some classes of protocols, it does not cope well with parameterized, multi-actor scenarios with inherent asynchrony. For example, the sliding window protocol is inexpressible in previously proposed session type systems. This paper describes System-A, a new typing language which overcomes many of the expressiveness limitations of prior work. System-A explicitly supports asynchrony and parallelism, as well as multiple forms of parameterization. We define System-A and show how it can be used for the static verification of a large class of asynchronous communication protocols.Comment: In Proceedings FOCLASA 2012, arXiv:1208.432

Scoped Synchronization Constraints for Large Scale Actor Systems

International audienceVery large scale systems of autonomous concurrent objects (Actors) require coordination models to meet two competing goals. On the one hand, the coordination models must allow Actors to dynamically modify protocols in order to adapt to requirement changes over the, likely extensive, lifetime of the system. On the other hand, the coordination models must enforce protocols on potentially uncooperative Actors, while preventing deadlocks caused by malicious or faulty Actors. To meet these competing requirements, we introduce a novel, scoped semantics for Synchronizers [7,6]—a coordination model based on declarative synchronization constraints. The mechanism used to limit the scope of the synchronization constraints is based on capabilities and works without central authority. We show that the mechanism closes an attack vector in the original Synchronizer approach which allowed malicious Actors to intentionally deadlock other Actors

interActors: A Model for Supporting Complex Communication in Concurrent Systems

In concurrent systems, such as multi-core computers, parallel systems, cloud computing systems, and systems involving mobile devices, processes interact with each other. Protocols for interactions among processes are increasingly complex and diverse, which is in part responsible for making programming of concurrent systems difficult. Particularly, in a concurrent program, the code for communication protocols often intermixes with the code for its functional behaviors, compromising modularity and reusability. There is a growing body of work on separating communication concerns of processes from their functional concerns. Although they achieve some degree of separation, they have some disadvantages. For example, the number of communication participants is fixed in some approaches, or in other approaches, communication mechanisms, such as for establishing the initial rendezvous for communication participants is left to the processes. In other words, existing approaches either offer static protocols that cannot handle dynamically evolving number of participants in interactions, or offer complex initialization steps that are left mixed with functional concerns. I propose interActors, a model for supporting complex communications in concurrent systems. I treat a communication as a first-class object which consists of outlets, through which processes can connect to it, and handlers, which are responsible for handling communication logics. Outlets establish a boundary between communications and processes in an application. New outlets can be created if necessary, to handle dynamically changed communication patterns at run-time. We say communications are self-driven because they have outlets and handlers that are active and therefore they can move interactions forward. More complex communications can be constructed by composing simpler communications. Operational semantics and compositional semantics are developed by extending the Actor model of concurrency with support for complex communication. A prototype implementation is developed using Scala and Akka actor library. With the intention of restricting arbitrarily complex code in communications, I developed Communication Specification Language (CSL), which excludes loops from communications and only allows a small set of statements and expressions. interActors are evaluated using case studies and comparison with Reo, a leading coordination model and language. The evaluation shows that interActors offer advantages in terms of programmability, reusability, and modularity