239 research outputs found
Parameterised Multiparty Session Types
For many application-level distributed protocols and parallel algorithms, the
set of participants, the number of messages or the interaction structure are
only known at run-time. This paper proposes a dependent type theory for
multiparty sessions which can statically guarantee type-safe, deadlock-free
multiparty interactions among processes whose specifications are parameterised
by indices. We use the primitive recursion operator from G\"odel's System T to
express a wide range of communication patterns while keeping type checking
decidable. To type individual distributed processes, a parameterised global
type is projected onto a generic generator which represents a class of all
possible end-point types. We prove the termination of the type-checking
algorithm in the full system with both multiparty session types and recursive
types. We illustrate our type theory through non-trivial programming and
verification examples taken from parallel algorithms and Web services usecases.Comment: LMCS 201
Pabble: parameterised Scribble
© 2014, The Author(s).Many parallel and distributed message-passing programs are written in a parametric way over available resources, in particular the number of nodes and their topologies, so that a single parallel program can scale over different environments. This article presents a parameterised protocol description language, Pabble, which can guarantee safety and progress in a large class of practical, complex parameterised message-passing programs through static checking. Pabble can describe an overall interaction topology, using a concise and expressive notation, designed for a variable number of participants arranged in multiple dimensions. These parameterised protocols in turn automatically generate local protocols for type checking parameterised MPI programs for communication safety and deadlock freedom. In spite of undecidability of endpoint projection and type checking in the underlying parameterised session type theory, our method guarantees the termination of end point projection and type checking
Hybrid Session Verification through Endpoint API Generation
© Springer-Verlag Berlin Heidelberg 2016.This paper proposes a new hybrid session verification methodology for applying session types directly to mainstream languages, based on generating protocol-specific endpoint APIs from multiparty session types. The API generation promotes static type checking of the behavioural aspect of the source protocol by mapping the state space of an endpoint in the protocol to a family of channel types in the target language. This is supplemented by very light run-time checks in the generated API that enforce a linear usage discipline on instances of the channel types. The resulting hybrid verification guarantees the absence of protocol violation errors during the execution of the session. We implement our methodology for Java as an extension to the Scribble framework, and use it to specify and implement compliant clients and servers for real-world protocols such as HTTP and SMTP
Choreographies in Practice
Choreographic Programming is a development methodology for concurrent
software that guarantees correctness by construction. The key to this paradigm
is to disallow mismatched I/O operations in programs, called choreographies,
and then mechanically synthesise distributed implementations in terms of
standard process models via a mechanism known as EndPoint Projection (EPP).
Despite the promise of choreographic programming, there is still a lack of
practical evaluations that illustrate the applicability of choreographies to
concrete computational problems with standard concurrent solutions. In this
work, we explore the potential of choreographies by using Procedural
Choreographies (PC), a model that we recently proposed, to write distributed
algorithms for sorting (Quicksort), solving linear equations (Gaussian
elimination), and computing Fast Fourier Transform. We discuss the lessons
learned from this experiment, giving possible directions for the usage and
future improvements of choreography languages
Explicit connection actions in multiparty session types
This work extends asynchronous multiparty session types (MPST) with explicit connection actions to support protocols with op- tional and dynamic participants. The actions by which endpoints are connected and disconnected are a key element of real-world protocols that is not treated in existing MPST works. In addition, the use cases motivating explicit connections often require a more relaxed form of mul- tiparty choice: these extensions do not satisfy the conservative restric- tions used to ensure safety in standard syntactic MPST. Instead, we de- velop a modelling-based approach to validate MPST safety and progress for these enriched protocols. We present a toolchain implementation, for distributed programming based on our extended MPST in Java, and a core formalism, demonstrating the soundness of our approach. We discuss key implementation issues related to the proposed extensions: a practi- cal treatment of choice subtyping for MPST progress, and multiparty correlation of dynamic binary connections
Deductive Verification of Parallel Programs Using Why3
The Message Passing Interface specification (MPI) defines a portable
message-passing API used to program parallel computers. MPI programs manifest a
number of challenges on what concerns correctness: sent and expected values in
communications may not match, resulting in incorrect computations possibly
leading to crashes; and programs may deadlock resulting in wasted resources.
Existing tools are not completely satisfactory: model-checking does not scale
with the number of processes; testing techniques wastes resources and are
highly dependent on the quality of the test set.
As an alternative, we present a prototype for a type-based approach to
programming and verifying MPI like programs against protocols. Protocols are
written in a dependent type language designed so as to capture the most common
primitives in MPI, incorporating, in addition, a form of primitive recursion
and collective choice. Protocols are then translated into Why3, a deductive
software verification tool. Source code, in turn, is written in WhyML, the
language of the Why3 platform, and checked against the protocol. Programs that
pass verification are guaranteed to be communication safe and free from
deadlocks.
We verified several parallel programs from textbooks using our approach, and
report on the outcome.Comment: In Proceedings ICE 2015, arXiv:1508.0459
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
Safe and scalable parallel programming with session types
Parallel programming is a technique that can coordinate and utilise multiple hardware resources simultaneously, to improve the overall computation performance. However, reasoning about the communication interactions between the resources is difficult. Moreover, scaling an application often leads to increased number and complexity of interactions, hence we need a systematic way to ensure the correctness of the communication aspects of parallel programs.
In this thesis, we take an interaction-centric view of parallel programming, and investigate applying and adapting the theory of Session Types, a formal typing discipline for structured interaction-based communication, to guarantee the lack of communication mismatches and deadlocks in concurrent systems. We focus on scalable, distributed parallel systems that use message-passing for communication. We explore programming language primitives, tools and frameworks to simplify parallel programming.
First, we present the design and implementation of Session C, a program ming toolchain for message-passing parallel programming. Session C can ensure deadlock freedom, communication safety and global progress through static type checking, and supports optimisations by refinements through session subtyping. Then we introduce Pabble, a protocol description language for designing parametric interaction protocols. The language can capture scalable interaction patterns found in parallel applications, and guarantees communication-safety and deadlock-freedom despite the undecidability of the underlying parameterised session type theory. Next, we demonstrate an application of Pabble in a workflow that combines Pabble protocols and computation kernel code describing the sequential computation behaviours, to generate a Message-Passing Interface (MPI) parallel application. The framework guarantees, by construction, that generated code are free from communication errors and deadlocks. Finally, we formalise an extension of binary session types and new language primitives for safe and efficient implementations of multiparty parallel applications in a binary server-client programming environment.
Our exploration with session-based parallel programming shows that it is a feasible and practical approach to guaranteeing communication aspects of complex, interaction-based scalable parallel programming.Open Acces
Session Communication and Integration
The scenario-based specification of a large distributed system is usually
naturally decomposed into various modules. The integration of specification
modules contrasts to the parallel composition of program components, and
includes various ways such as scenario concatenation, choice, and nesting. The
recent development of multiparty session types for process calculi provides
useful techniques to accommodate the protocol modularisation, by encoding
fragments of communication protocols in the usage of private channels for a
class of agents. In this paper, we extend forgoing session type theories by
enhancing the session integration mechanism. More specifically, we propose a
novel synchronous multiparty session type theory, in which sessions are
separated into the communicating and integrating levels. Communicating sessions
record the message-based communications between multiple agents, whilst
integrating sessions describe the integration of communicating ones. A
two-level session type system is developed for pi-calculus with syntactic
primitives for session establishment, and several key properties of the type
system are studied. Applying the theory to system description, we show that a
channel safety property and a session conformance property can be analysed.
Also, to improve the utility of the theory, a process slicing method is used to
help identify the violated sessions in the type checking.Comment: A short version of this paper is submitted for revie
Session Types for Broadcasting
Up to now session types have been used under the assumptions of point to
point communication, to ensure the linearity of session endpoints, and reliable
communication, to ensure send/receive duality. In this paper we define a
session type theory for broadcast communication semantics that by definition do
not assume point to point and reliable communication. Our session framework
lies on top of the parametric framework of broadcasting psi-calculi, giving
insights on developing session types within a parametric framework. Our session
type theory enjoys the properties of soundness and safety. We further believe
that the solutions proposed will eventually provide a deeper understanding of
how session types principles should be applied in the general case of
communication semantics.Comment: In Proceedings PLACES 2014, arXiv:1406.331
- …