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Dive into the research topics where Nicholas Ng is active.

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Featured researches published by Nicholas Ng.


TOOLS'12 Proceedings of the 50th international conference on Objects, Models, Components, Patterns | 2012

Multiparty session c: safe parallel programming with message optimisation

Nicholas Ng; Nobuko Yoshida; Kohei Honda

This paper presents a new efficient programming toolchain for message-passing parallel algorithms which can fully ensure, for any typable programs and for any execution path, deadlock-freedom, communication safety and global progress through a static checking. The methodology is embodied as a multiparty session-based programming environment for C and its runtime libraries, which we call Session C. Programming starts from specifying a global protocol for a target parallel algorithm, using a protocol description language. From this global protocol, the projection algorithm generates endpoint protocols, based on which each endpoint C program is designed and implemented with a small number of concise session primitives. The endpoint protocol can further be refined to a more optimised protocol through subtyping for asynchronous communication, preserving original safety guarantees. The underlying theory can ensure that the complexity of the toolchain stays in polynomial time against the size of programs. We apply this framework to representative parallel algorithms with complex communication topologies. The benchmark results show that Session C performs competitively against MPI.


trustworthy global computing | 2013

The Scribble Protocol Language

Nobuko Yoshida; Raymond Hu; Rumyana Neykova; Nicholas Ng

This paper describes a brief history of how Kohei Honda initiated the Scribble project, and summarises the current status of Scribble.


international conference on coordination models and languages | 2011

Safe parallel programming with session Java

Nicholas Ng; Nobuko Yoshida; Olivier Pernet; Raymond Hu; Yiannos Kryftis

The session-typed programming language Session Java (SJ) has proved to be an effective tool for distributed programming, promoting structured programming for communications and compile-time safety. This paper investigates the use of SJ for session-typed parallel programming, and introduces new language primitives for chained iteration and multi-channel communication. These primitives allow the efficient coordination of parallel computation across multiple processes, thus enabling SJ to express the complex communication topologies often used by parallel algorithms. We demonstrate that the new primitives yield clearer and safer code for pipeline, ring and mesh topologies through implementations of representative parallel algorithms. We then present a semantics and session typing system including the new primitives, and prove type soundness and deadlock-freedom for our implementations. The benchmark results show that the new SJ is substantially faster than the original SJ and performs competitively against MPJ Express used as reference.


Foundations and Trends in Programming Languages archive | 2016

Behavioral Types in Programming Languages

Davide Ancona; Viviana Bono; Mario Bravetti; Joana Campos; Giuseppe Castagna; Pierre-Malo Deniélou; Nils Gesbert; Elena Giachino; Raymond Hu; Einar Broch Johnsen; Francisco Martins; Viviana Mascardi; Fabrizio Montesi; Rumyana Neykova; Nicholas Ng; Luca Padovani; Vasco Thudichum Vasconcelos; Nobuko Yoshida

A recent trend in programming language research is to use behavioral type theory to ensure various correctness properties of large-scale, communication-intensive systems. Behavioral types encompass concepts such as interfaces, communication protocols, contracts, and choreography. The successful application of behavioral types requires a solid understanding of several practical aspects, from their representation in a concrete programming language, to their integration with other programming constructs such as methods and functions, to design and monitoring methodologies that take behaviors into account. Behavioral Types in Programming Languages provides the reader with the first comprehensive overview of the state of the art of these practical aspects, which are summarized as the pragmatics of behavioral types. Each section covers a particular programming paradigm or methodology, providing an ideal reference for programming languages researchers interested the topic, and in identifying the areas as yet unexplored.


conference on object oriented programming systems languages and applications | 2015

Protocol-based verification of message-passing parallel programs

Hugo A. López; Eduardo R. B. Marques; Francisco Martins; Nicholas Ng; César Santos; Vasco Thudichum Vasconcelos; Nobuko Yoshida

We present ParTypes, a type-based methodology for the verification of Message Passing Interface (MPI) programs written in the C programming language. The aim is to statically verify programs against protocol specifications, enforcing properties such as fidelity and absence of deadlocks. We develop a protocol language based on a dependent type system for message-passing parallel programs, which includes various communication operators, such as point-to-point messages, broadcast, reduce, array scatter and gather. For the verification of a program against a given protocol, the protocol is first translated into a representation read by VCC, a software verifier for C. We successfully verified several MPI programs in a running time that is independent of the number of processes or other input parameters. This contrasts with alternative techniques, notably model checking and runtime verification, that suffer from the state-explosion problem or that otherwise depend on parameters to the program itself. We experimentally evaluated our approach against state-of-the-art tools for MPI to conclude that our approach offers a scalable solution.


parallel, distributed and network-based processing | 2014

Pabble: Parameterised Scribble for Parallel Programming

Nicholas Ng; Nobuko Yoshida

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 paper 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 endpoint projection and type checking.


compiler construction | 2016

Static deadlock detection for concurrent go by global session graph synthesis

Nicholas Ng; Nobuko Yoshida

Go is a programming language developed at Google, with channel-based concurrent features based on CSP. Go can detect global communication deadlocks at runtime when all threads of execution are blocked, but deadlocks in other paths of execution could be undetected. We present a new static analyser for concurrent Go code to find potential communication errors such as communication mismatch and deadlocks at compile time. Our tool extracts the communication operations as session types, which are then converted into Communicating Finite State Machines (CFSMs). Finally, we apply a recent theoretical result on choreography synthesis to generate a global graph representing the overall communication pattern of a concurrent program. If the synthesis is successful, then the program is free from communication errors. We have implemented the technique in a tool, and applied it to analyse common Go concurrency patterns and an open source application with over 700 lines of code.


EuroMPI'12 Proceedings of the 19th European conference on Recent Advances in the Message Passing Interface | 2012

Verification of MPI programs using session types

Kohei Honda; Eduardo R. B. Marques; Francisco Martins; Nicholas Ng; Vasco Thudichum Vasconcelos; Nobuko Yoshida

Developing safe, concurrent (and parallel) software systems is a hard task in multiple aspects, particularly the sharing of information and the synchronization among multiple participants of the system. In the message passing paradigm, this is achieved by sending and receiving messages among different participants, raising a number of verification problems. For instance, exchanging messages in a wrong order may prevent the system from progressing, causing a deadlock.MPI is the most commonly used protocol for high-performance, message-based parallel programs, and the need for formal verification approaches is well acknowledged by much recent work (e.g., see [1]).


compiler construction | 2015

Protocols by Default

Nicholas Ng; José Gabriel F. Coutinho; Nobuko Yoshida

This paper presents a code generation framework for type-safe and deadlock-free Message Passing Interface (MPI) programs. The code generation process starts with the definition of the global topology using a protocol specification language based on parameterised multiparty session types (MPST). An MPI parallel program backbone is automatically generated from the global specification. The backbone code can then be merged with the sequential code describing the application behaviour, resulting in a complete MPI program. This merging process is fully automated through the use of an aspect-oriented compilation approach. In this way, programmers only need to supply the intended communication protocol and provide sequential code to automatically obtain parallelised programs that are guaranteed free from communication mismatch, type errors or deadlocks. The code generation framework also integrates an optimisation method that overlaps communication and computation, and can derive not only representative parallel programs with common parallel patterns (such as ring and stencil), but also distributed applications from any MPST protocols. We show that our tool generates efficient and scalable MPI applications, and improves productivity of programmers. For instance, our benchmarks involving representative parallel and application-specific patterns speed up sequential execution by up to 31 times and reduce programming effort by an average of 39%.


service oriented computing and applications | 2015

Pabble: parameterised Scribble

Nicholas Ng; Nobuko Yoshida

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.

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Julien Lange

Imperial College London

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Raymond Hu

Imperial College London

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Bernardo Toninho

Universidade Nova de Lisboa

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Kohei Honda

Queen Mary University of London

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