TLS The Erlang/OTP Way

Published in ACM SIGPLAN Erlang Workshop (Erlang), 2023

The Transport Layer Security (TLS) protocol is one of the most used protocols to ensure data privacy, integrity and authenticity on the Internet. Erlang/OTP’s TLS implementation is widely used in industry, and especially in the telecommunication sector.

Towards Gradual Checking of Reference Capabilities

Published in Virtual Machines and Intermediate Languages Workshop (VMIL), 2019

Concurrent and parallel programming is difficult due to the presence of memory side-effects, which may introduce data races. Type qualifiers, such as reference capabilities, can remove data races by restricting sharing of mutable data. Unfortunately, reference capability languages are an all-in or nothing game, i.e., all the types must be annotated with reference capabilities. In this work in progress, we propose to mix the ideas from the reference capability literature with gradual typing, leading to gradual reference capabilities.

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Run, Actor, Run

Published in Workshop on Programming based on Actors, Agents, and Decentralized Control (AGERE!), 2019

The actor paradigm supports the natural expression of concurrency. It has inspired the development of several actor-based languages, whose adoption depends, to a large extent, on the runtime characteristics (i.e.,the performance and scaling behaviour) of programs written in these languages. This paper investigates the relative runtime characteristics of Akka, CAF and Pony, based on the Savina benchmarks.We observe that the scaling of many of the Savina benchmarks does not reflect their categorization (into essentially sequential, concurrent and parallel), that many programs have similar runtime characteristics, and that their runtime behaviour may drastically change nature (e.g.,go from essentially sequential to parallel) by tweaking some parameters. These observations lead to our proposal of a single benchmark program which we designed so that through tweaking of some knobs (we hope) we can simulate most of the programs of the Savina suite.

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Developing a Monadic Type Checker for an Object-Oriented Language

Published in International Conference on Software Language Engineering (SLE), 2019

Functional programming languages are well-suited for developing compilers, and compilers for functional languages are often themselves written in a functional language. Functional abstractions, such as monads, allow abstracting away some of the repetitive structure of a compiler, removing boilerplate code and making extensions simpler. Even so,functional languages are rarely used to implement compilers for languages of other paradigms. This paper reports on the experience of a four-year long project where we developed a compiler for a concurrent, object-oriented language using the functional language Haskell.The focus of the paper is the implementation of the typechecker, but the design works well in static analysis tools, such as tracking uniqueness of variables to ensure data-race freedom. The paper starts from a simple type checker to which we add more complex features, such as type state, with minimal changes to the overall initial design.

Godot: All the Benefits of Implicit and Explicit Futures

Published in ECOOP, 2019

Concurrent programs often make use of futures, handles to the results of asynchronous operations. Futures provide means to communicate not yet computed results, and simplify the implementation of operations that synchronise on the result of such asynchronous operations. Futures can be characterised as implicit or explicit, depending on the typing discipline used to type them.

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Attached and detached closures in actors

Published in AGERE, 2018

Expressive actor models combine aspects of functional programming into the pure actor model enriched with futures. Such functional features include first-class closures which can be passed between actors and chained on futures. Combined with mutable objects, this opens the door to race conditions. In some situations, closures may not be evaluated by the actor that created them yet may access fields or objects owned by that actor. In other situations, closures may be safely fired off to run as a separate task.

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Forward to a Promising Future

Published in COORDINATION, 2018

In many actor-based programming models, asynchronous method calls communicate their results using futures, where the fulfilment occurs under-the-hood. Promises play a similar role to futures, except that they must be explicitly created and explicitly fulfilled; this makes promises more flexible than futures, though promises lack fulfilment guarantees: they can be fulfilled once, multiple times or not at all. Unfortunately, futures are too rigid to exploit many available concurrent and parallel patterns. For instance, many computations block on a future to get its result only to return that result immediately (to fulfil their own future). To make futures more flexible, we explore a construct, forward, that delegates the responsibility for fulfilling the current implicit future to another computation. Forward reduces synchronisation and gives futures promise-like capabilities. This paper presents a formalisation of the forward construct, defined in a high-level source language, and a compilation strategy from the high-level language to a low-level, promised-based target language. The translation is shown to preserve semantics. Based on this foundation, we describe the implementation of forward in the parallel, actor-based language Encore, which compiles to C.

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A Survey of Active Object Languages

Published in Journal ACM Computing Surveys (CSUR), Volume 50 Issue 5, November 2017. Article No. 76, 2017

To program parallel systems efficiently and easily, a wide range of programming models have been proposed, each with different choices concerning synchronization and communication between parallel entities. Among them, the actor model is based on loosely coupled parallel entities that communicate by means of asynchronous messages and mailboxes. Some actor languages provide a strong integration with object-oriented concepts; these are often called active object languages. This article reviews four major actor and active object languages and compares them according to carefully chosen dimensions that cover central aspects of the programming paradigms and their implementation.

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ParT: An Asynchronous Parallel Abstraction for Speculative Pipeline Computations

Published in COORDINATION, 2016

The ubiquity of multicore computers has forced programming language designers to rethink how languages express parallelism and concurrency. This has resulted in new language constructs and new combinations or revisions of existing constructs. In this line, we extended the programming languages Encore (actor-based), and Clojure (functional) with an asynchronous parallel abstraction called ParT, a data structure that can dually be seen as a collection of asynchronous values (integrating with futures) or a handle to a parallel computation, plus a collection of combinators for manipulating the data structure. The combinators can express parallel pipelines and speculative parallelism. This paper presents a typed calculus capturing the essence of ParT, abstracting away from details of the Encore and Clojure programming languages. The calculus includes tasks, futures, and combinators similar to those of Orc but implemented in a non-blocking fashion. Furthermore, the calculus strongly mimics how ParT is implemented, and it can serve as the basis for adaptation of ParT into different languages and for further extensions.

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Parallel Objects for Multicores: A Glimpse at the Parallel Language Encore

Published in SFM 2015: Formal Methods for Multicore Programming, 2015

The age of multi-core computers is upon us, yet current programming languages, typically designed for single-core computers and adapted post hoc for multi-cores, remain tied to the constraints of a sequential mindset and are thus in many ways inadequate. New programming language designs are required that break away from this old-fashioned mindset. To address this need, we have been developing a new programming language called Encore, in the context of the European Project UpScale. The paper presents a motivation for the Encore language, examples of its main constructs, several larger programs, a formalisation of its core, and a discussion of some future directions our work will take. The work is ongoing and we started more or less from scratch. That means that a lot of work has to be done, but also that we need not be tied to decisions made for sequential language designs. Any design decision can be made in favour of good performance and scalability. For this reason, Encore offers an interesting platform for future exploration into object-oriented parallel programming.

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