arXiv subjects

Fabrizio Montesi

Publications and source records attributed to Fabrizio Montesi.

At least 55 records · Page 3Linked to original sources

arXiv2018

Connectors meet Choreographies

We present Cho-Reo-graphies (CR), a new language model that unites two powerful programming paradigms for concurrent software based on communicating processes: Choreographic Programming and Exogenous Coordination. In CR, programmers specify the desired communications among processes using a choreography, and define how communications should be concretely animated by connectors given as constraint automata (e.g., synchronous barriers and asynchronous multi-casts). CR is the first choreography calculus where different communication semantics (determined by connectors) can be freely mixed; since connectors are user-defined, CR also supports many communication semantics that were previously unavailable for choreographies. We develop a static analysis that guarantees that a choreography in CR and its user-defined connectors are compatible, define a compiler from choreographies to a process calculus based on connectors, and prove that compatibility guarantees deadlock-freedom of the compiled process implementations.

cs.PL↗

arXiv2018

Classical Transitions

We introduce the calculus of Classical Transitions (CT), which extends the research line on the relationship between linear logic and processes to labelled transitions. The key twist from previous work is registering parallelism in typing judgements, by generalising linear logic judgements from one sequents to many (hypersequents). This allows us to bridge the gap between the structures of operators used as proof terms in previous work and those of the standard π-calculus (in particular parallel operator and restriction). The proof theory of CT allows for new proof transformations, which we show correspond to a labelled transition system (LTS) for processes. We prove that CT enjoys subject reduction and progress.

cs.LO↗

arXiv2018

Classical Higher-Order Processes

Classical Processes (CP) is a calculus where the proof theory of classical linear logic types communicating processes with mobile channels, a la pi-calculus. Its construction builds on a recent propositions as types correspondence between session types and propositions in linear logic. Desirable properties such as type preservation under reductions and progress come for free from the metatheory of linear logic. We contribute to this research line by extending CP with code mobility. We generalise classical linear logic to capture higher-order (linear) reasoning on proofs, which yields a logical reconstruction of (a variant of) the Higher-Order pi-calculus (HOpi). The resulting calculus is called Classical Higher-Order Processes (CHOP). We explore the metatheory of CHOP, proving that its semantics enjoys type preservation and progress (terms do not get stuck). We also illustrate the expressivity of CHOP through examples, derivable syntax sugar, and an extension to multiparty sessions. Lastly, we define a translation from CHOP to CP, which encodes mobility of process code into reference passing.

cs.LO↗

arXiv2018

Choreographies for Reactive Programming

Modular programming is a cornerstone in software development, as it allows to build complex systems from the assembly of simpler components, and support reusability and substitution principles. In a distributed setting, component assembly is supported by communication that is often required to follow a prescribed protocol of interaction. In this paper, we present a language for the modular development of distributed systems, where the assembly of components is supported by a choreography that specifies the communication protocol. Our language allows to separate component behaviour, given in terms of reactive data ports, and choreographies, specified as first class entities. This allows us to consider reusability and substitution principles for both components and choreographies. We show how our model can be compiled into a more operational perspective in a provably-correct way, and we present a typing discipline that addresses communication safety and progress of systems, where a notion of substitutability naturally arises.

cs.PL↗

arXiv2017

On Asynchrony and Choreographies

Choreographic Programming is a paradigm for the development of concurrent software, where deadlocks are prevented syntactically. However, choreography languages are typically synchronous, whereas many real-world systems have asynchronous communications. Previous attempts at enriching choreographies with asynchrony rely on ad-hoc constructions, whose adequacy is only argued informally. In this work, we formalise the properties that an asynchronous semantics for choreographies should have: messages can be sent without the intended receiver being ready, and all sent messages are eventually received. We explore how out-of-order execution, used in choreographies for modelling concurrency, can be exploited to endow choreographies with an asynchronous semantics. Our approach satisfies the properties we identified. We show how our development yields a pleasant correspondence with FIFO-based asynchronous messaging, modelled in a process calculus, and discuss how it can be adopted in more complex choreography models.

cs.PL↗

arXiv2017

Communications in Choreographies, Revisited

Choreographic Programming is a paradigm for developing correct-by-construction concurrent programs, by writing high-level descriptions of the desired communications and then synthesising process implementations automatically. So far, choreographic programming has been explored in the monadic setting: interaction terms express point-to-point communications of a single value. However, real-world systems often rely on interactions of polyadic nature, where multiple values are communicated among two or more parties, like multicast, scatter-gather, and atomic exchanges. We introduce a new model for choreographic programming equipped with a primitive for grouped interactions that subsumes all the above scenarios. Intuitively, grouped interactions can be thought of as being carried out as one single interaction. In practice, they are implemented by processes that carry them out in a concurrent fashion. After formalising the intuitive semantics of grouped interactions, we prove that choreographic programs and their implementations are correct and deadlock-free by construction.

cs.PL↗

arXiv2017

That's Enough: Asynchrony with Standard Choreography Primitives

Choreographies are widely used for the specification of concurrent and distributed software architectures. Since asynchronous communications are ubiquitous in real-world systems, previous works have proposed different approaches for the formal modelling of asynchrony in choreographies. Such approaches typically rely on ad-hoc syntactic terms or semantics for capturing the concept of messages in transit, yielding different formalisms that have to be studied separately. In this work, we take a different approach, and show that such extensions are not needed to reason about asynchronous communications in choreographies. Rather, we demonstrate how a standard choreography calculus already has all the needed expressive power to encode messages in transit (and thus asynchronous communications) through the primitives of process spawning and name mobility. The practical consequence of our results is that we can reason about real-world systems within a choreography formalism that is simpler than those hitherto proposed.

cs.PL↗

arXiv2017

Microservices: a Language-based Approach

Microservices is an emerging development paradigm where software is obtained by composing autonomous entities, called (micro)services. However, microservice systems are currently developed using general-purpose programming languages that do not provide dedicated abstractions for service composition. Instead, current practice is focused on the deployment aspects of microservices, in particular by using containerization. In this chapter, we make the case for a language-based approach to the engineering of microservice architectures, which we believe is complementary to current practice. We discuss the approach in general, and then we instantiate it in terms of the Jolie programming language.

cs.PL↗

arXiv2017

Microservices: yesterday, today, and tomorrow

Microservices is an architectural style inspired by service-oriented computing that has recently started gaining popularity. Before presenting the current state-of-the-art in the field, this chapter reviews the history of software architecture, the reasons that led to the diffusion of objects and services first, and microservices later. Finally, open problems and future challenges are introduced. This survey primarily addresses newcomers to the discipline, while offering an academic viewpoint on the topic. In addition, we investigate some practical issues and point out some potential solutions.

cs.SE↗

arXiv2017

The Paths to Choreography Extraction

Choreographies are global descriptions of interactions among concurrent components, most notably used in the settings of verification (e.g., Multiparty Session Types) and synthesis of correct-by-construction software (Choreographic Programming). They require a top-down approach: programmers first write choreographies, and then use them to verify or synthesize their programs. However, most existing software does not come with choreographies yet, which prevents their application. To attack this problem, we propose a novel methodology (called choreography extraction) that, given a set of programs or protocol specifications, automatically constructs a choreography that describes their behavior. The key to our extraction is identifying a set of paths in a graph that represents the symbolic execution of the programs of interest. Our method improves on previous work in several directions: we can now deal with programs that are equipped with a state and internal computation capabilities; time complexity is dramatically better; we capture programs that are correct but not necessarily synchronizable, i.e., they work because they exploit asynchronous communication.

cs.PL↗

arXiv2016

A Language for the Declarative Composition of Concurrent Protocols

A recent study of bugs in real-world concurrent and distributed systems found that, while implementations of individual protocols tend to be robust, the composition of multiple protocols and its interplay with internal computation is the culprit for most errors. Multiparty Session Types and Choreographic Programming are methodologies for developing correct-by-construction concurrent and distributed software, based on global descriptions of communication flows. However, protocol composition is either limited or left unchecked. Inspired by these two methodologies, in this work we present a new language model for the safe composition of protocols, called Procedural Choreographies (PC). Protocols in PC are procedures, parameterised on the processes that enact them. Procedures define communications declaratively using global descriptions, and programs are written by invoking and composing these procedures. An implementation in terms of a process model is then mechanically synthesised, guaranteeing correctness and deadlock-freedom. We study PC in the settings of synchronous and asynchronous communications, and illustrate its expressivity with some representative examples.

cs.PL↗

arXiv2016

Circuit Breakers, Discovery, and API Gateways in Microservices

We review some of the most widely used patterns for the programming of microservices: circuit breaker, service discovery, and API gateway. By systematically analysing different deployment strategies for these patterns, we reach new insight especially for the application of circuit breakers. We also evaluate the applicability of Jolie, a language for the programming of microservices, for these patterns and report on other standard frameworks offering similar solutions. Finally, considerations for future developments are presented.

cs.SE↗

arXiv2016

Process-aware web programming with Jolie

We extend the Jolie programming language to capture the native modelling of process-aware web information systems, i.e., web information systems based upon the execution of business processes. Our main contribution is to offer a unifying approach for the programming of distributed architectures on the web, which can capture web servers, stateful process execution, and the composition of services via mediation. We discuss applications of this approach through a series of examples that cover, e.g., static content serving, multiparty sessions, and the evolution of web systems. Finally, we present a performance evaluation that includes a comparison of Jolie-based web systems to other frameworks and a measurement of its scalability.

cs.DC↗

arXiv2016

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.

cs.PL↗

arXiv2016

Refinement types in Jolie

Jolie is the first language for microservices and it is currently dynamically type checked. This paper considers the opportunity to integrate dynamic and static type checking with the introduction of refinement types, verified via SMT solver. The integration of the two aspects allows a scenario where the static verification of internal services and the dynamic verification of (potentially malicious) external services cooperates in order to reduce testing effort and enhancing security.

cs.SE↗

arXiv2015

Data-driven Workflows for Microservices

Microservices is an architectural style inspired by service-oriented computing that has recently started gaining popularity. Jolie is a programming language based on the microservices paradigm: the main building block of Jolie systems are services, in contrast to, e.g., functions or objects. The primitives offered by the Jolie language elicit many of the recurring patterns found in microservices, like load balancers and structured processes. However, Jolie still lacks some useful constructs for dealing with message types and data manipulation that are present in service-oriented computing. In this paper, we focus on the possibility of expressing choices at the level of data types, a feature well represented in standards for Web Services, e.g., WSDL. We extend Jolie to support such type choices and show the impact of our implementation on some of the typical scenarios found in microservice systems. This shows how computation can move from a process-driven to a data-driven approach, and leads to the preliminary identification of recurring communication patterns that can be shaped as design patterns.

cs.PL↗

arXiv2015

Kickstarting Choreographic Programming

We present an overview of some recent efforts aimed at the development of Choreographic Programming, a programming paradigm for the production of concurrent software that is guaranteed to be correct by construction from global descriptions of communication behaviour.

cs.PL↗

arXiv2013

Amending Choreographies

Choreographies are global descriptions of system behaviors, from which the local behavior of each endpoint entity can be obtained automatically through projection. To guarantee that its projection is correct, i.e. it has the same behaviors of the original choreography, a choreography usually has to respect some coherency conditions. This restricts the set of choreographies that can be projected. In this paper, we present a transformation for amending choreographies that do not respect common syntactic conditions for projection correctness. Specifically, our transformation automatically reduces the amount of concurrency, and it infers and adds hidden communications that make the resulting choreography respect the desired conditions, while preserving its behavior.

cs.PL↗