Real-time analysis of MPI programs for NoC-based many-cores using time division multiplexing

Worst-case execution time (WCET) analysis is crucial for designing hard real-time systems. While the WCET of tasks in a single core system can be upper bounded in isolation, the tasks in a many-core system are subject to shared memory interferences which impose high overestimation of the WCET bounds. However, many-core-based massively parallel applications will enter the area of real-time systems in the years ahead. Explicit message-passing and a clear separation of computation and communication facilitates WCET analysis for those programs. A standard programming model for message-based communication is the message passing interface (MPI). It provides an application independent interface for different standard communication operations (e.g. broadcast, gather, ...). Thereby, it uses efficient communication patterns with deterministic behaviour. In applying these known structures, we target to provide a WCET analysis for communication that is reusable for different applications if the communication is executed on the same underlying platform. Hence, the analysis must be performed once per hardware platform and can be reused afterwards with only adapting several parameters such as the number of nodes participating in that communication. Typically, the processing elements of many-core platforms are connected via a Network-on-Chip (NoC) and apply techniques such as time-division multiplexing (TDM) to provide guaranteed services for the network. Hence, the hardware and the applied technique for guaranteed service needs to facilitate this reusability of the analysis as well. In this work we review different general-purpose TDM schedules that enable a WCET approximation independent of the placement of tasks on processing elements of a many-core which uses a NoC with torus topology. Furthermore, we provide two new schedules that show a similar performance as the state-of-the-art schedules but additionally serve situations where the presented state-of-the-art schedules perform poorly. Based on these schedules a procedure for the WCET analysis of the communication patterns used in MPI is proposed. Finally, we show how to apply the results of the analysis to calculate the WCET upper bound for a complete MPI program. Detailed insights in the performance of the applied TDM schedules are provided by comparing the schedules to each other in terms of timing. Additionally, we discuss the exhibited timing of the general-purpose schedules compared to a state-of-the-art application specific TDM schedule to put in relation both types of schedules. We apply the proposed procedure to several standard types of communication provided in MPI and compare different patterns that are used to implement a specific communication. Our evaluation investigates the communications’ building blocks of the timing bounds and shows the tremendous impact of choosing the appropriate communication pattern. Finally, a case study demonstrates the application of the presented procedure to a complete MPI program. With the method proposed in this work it is possible to perform a reusable WCET timing analysis for the communication in a NoC that is independent of the placement of tasks on the chip. Moreover, as the applied schedules are not optimized for a specific application but can be used for all applications in the same way, there are only marginal changes in the timing of the communication when the software is adapted or updated. Thus, there is no need to perform the timing analysis from scratch in such cases

Behavioural Types: from Theory to Tools

This book presents research produced by members of COST Action IC1201: Behavioural Types for Reliable Large-Scale Software Systems (BETTY), a European research network that was funded from October 2012 to October 2016. The technical theme of BETTY was the use of behavioural type systems in programming languages, to specify and verify properties of programs beyond the traditional use of type systems to describe data processing. A significant area within behavioural types is session types, which concerns the use of type-theoretic techniques to describe communication protocols so that static typechecking or dynamic monitoring can verify that protocols are implemented correctly. This is closely related to the topic of choreography, in which system design starts from a description of the overall communication flows. Another area is behavioural contracts, which describe the obligations of interacting agents in a way that enables blame to be attributed to the agent responsible for failed interaction. Type-theoretic techniques can also be used to analyse potential deadlocks due to cyclic dependencies between inter-process interactions. BETTY was organised into four Working Groups: (1) Foundations; (2) Security; (3) Programming Languages; (4) Tools and Applications. Working Groups 1–3 produced “state-of-the-art reports”, which originally intended to take snapshots of the field at the time the network started, but grew into substantial survey articles including much research carried out during the network [1–3]. The situation for Working Group 4 was different. When the network started, the community had produced relatively few implementations of programming languages or tools. One of the aims of the network was to encourage more implementation work, and this was a great success. The community as a whole has developed a greater interest in putting theoretical ideas into practice. The sixteen chapters in this book describe systems that were either completely developed, or substantially extended, during BETTY. The total of 41 co-authors represents a significant proportion of the active participants in the network (around 120 people who attended at least one meeting). The book is a report on the new state of the art created by BETTY in xv xvi Preface the area of Working Group 4, and the title “Behavioural Types: from Theory to Tools” summarises the trajectory of the community during the last four years. The book begins with two tutorials by Atzei et al. on contract-oriented design of distributed systems. Chapter 1 introduces the CO2 contract specifi- cation language and the Diogenes toolchain. Chapter 2 describes how timing constraints can be incorporated into the framework and checked with the CO2 middleware. Part of the CO2 middleware is a monitoring system, and the theme of monitoring continues in the next two chapters. In Chapter 3, Attard et al. present detectEr, a runtime monitoring tool for Erlang programs that allows correctness properties to be expressed in Hennessy-Milner logic. In Chapter 4, which is the first chapter about session types, Neykova and Yoshida describe a runtime verification framework for Python programs. Communication protocols are specified in the Scribble language, which is based on multiparty session types. The next three chapters deal with choreographic programming. In Chap- ter 5, Debois and Hildebrandt present a toolset for working with dynamic condition response (DCR) graphs, which are a graphical formalism for choreography. Chapter 6, by Lange et al., continues the graphical theme with ChorGram, a tool for synthesising global graphical choreographies from collections of communicating finite-state automata. Giallorenzo et al., in Chapter 7, consider runtime adaptation. They describe AIOCJ, a choreographic programming language in which runtime adaptation is supported with a guarantee that it doesn’t introduce deadlocks or races. Deadlock analysis is important in other settings too, and there are two more chapters about it. In Chapter 8, Padovani describes the Hypha tool, which uses a type-based approach to check deadlock-freedom and lock-freedom of systems modelled in a form of pi-calculus. In Chapter 9, Garcia and Laneve present a tool for analysing deadlocks in Java programs; this tool, called JaDA, is based on a behavioural type system. The next three chapters report on projects that have added session types to functional programming languages in order to support typechecking of communication-based code. In Chapter 10, Orchard and Yoshida describe an implementation of session types in Haskell, and survey several approaches to typechecking the linearity conditions required for safe session implemen- tation. In Chapter 11, Melgratti and Padovani describe an implementation of session types in OCaml. Their system uses runtime linearity checking. In Chapter 12, Lindley and Morris describe an extension of the web programming language Links with session types; their work contrasts with the previous two chapters in being less constrained by an existing language design. Continuing the theme of session types in programming languages, the next two chapters describe two approaches based on Java. Hu’s work, presented in Chapter 13, starts with the Scribble description of a multiparty session type and generates an API in the form of a collection of Java classes, each class containing the communication methods that are available in a particular state of the protocol. Dardha et al., in Chapter 14, also start with a Scribble specification. Their StMungo tool generates an API as a single class with an associated typestate specification to constrain sequences of method calls. Code that uses the API can be checked for correctness with the Mungo typechecker. Finally, there are two chapters about programming with the MPI libraries. Chapter 15, by Ng and Yoshida, uses an extension of Scribble, called Pabble, to describe protocols that parametric in the number of runtime roles. From a Pabble specification they generate C code that uses MPI for communication and is guaranteed correct by construction. Chapter 16, by Ng et al., describes the ParTypes framework for analysing existing C+MPI programs with respect to protocols defined in an extension of Scribble. We hope that the book will serve a useful purpose as a report on the activities of COST Action IC1201 and as a survey of programming languages and tools based on behavioural types

Behavioural Types: from Theory to Tools

This book presents research produced by members of COST Action IC1201: Behavioural Types for Reliable Large-Scale Software Systems (BETTY), a European research network that was funded from October 2012 to October 2016. The technical theme of BETTY was the use of behavioural type systems in programming languages, to specify and verify properties of programs beyond the traditional use of type systems to describe data processing. A significant area within behavioural types is session types, which concerns the use of type-theoretic techniques to describe communication protocols so that static typechecking or dynamic monitoring can verify that protocols are implemented correctly. This is closely related to the topic of choreography, in which system design starts from a description of the overall communication flows. Another area is behavioural contracts, which describe the obligations of interacting agents in a way that enables blame to be attributed to the agent responsible for failed interaction. Type-theoretic techniques can also be used to analyse potential deadlocks due to cyclic dependencies between inter-process interactions. BETTY was organised into four Working Groups: (1) Foundations; (2) Security; (3) Programming Languages; (4) Tools and Applications. Working Groups 1–3 produced “state-of-the-art reports”, which originally intended to take snapshots of the field at the time the network started, but grew into substantial survey articles including much research carried out during the network [1–3]. The situation for Working Group 4 was different. When the network started, the community had produced relatively few implementations of programming languages or tools. One of the aims of the network was to encourage more implementation work, and this was a great success. The community as a whole has developed a greater interest in putting theoretical ideas into practice. The sixteen chapters in this book describe systems that were either completely developed, or substantially extended, during BETTY. The total of 41 co-authors represents a significant proportion of the active participants in the network (around 120 people who attended at least one meeting). The book is a report on the new state of the art created by BETTY in xv xvi Preface the area of Working Group 4, and the title “Behavioural Types: from Theory to Tools” summarises the trajectory of the community during the last four years. The book begins with two tutorials by Atzei et al. on contract-oriented design of distributed systems. Chapter 1 introduces the CO2 contract specifi- cation language and the Diogenes toolchain. Chapter 2 describes how timing constraints can be incorporated into the framework and checked with the CO2 middleware. Part of the CO2 middleware is a monitoring system, and the theme of monitoring continues in the next two chapters. In Chapter 3, Attard et al. present detectEr, a runtime monitoring tool for Erlang programs that allows correctness properties to be expressed in Hennessy-Milner logic. In Chapter 4, which is the first chapter about session types, Neykova and Yoshida describe a runtime verification framework for Python programs. Communication protocols are specified in the Scribble language, which is based on multiparty session types. The next three chapters deal with choreographic programming. In Chap- ter 5, Debois and Hildebrandt present a toolset for working with dynamic condition response (DCR) graphs, which are a graphical formalism for choreography. Chapter 6, by Lange et al., continues the graphical theme with ChorGram, a tool for synthesising global graphical choreographies from collections of communicating finite-state automata. Giallorenzo et al., in Chapter 7, consider runtime adaptation. They describe AIOCJ, a choreographic programming language in which runtime adaptation is supported with a guarantee that it doesn’t introduce deadlocks or races. Deadlock analysis is important in other settings too, and there are two more chapters about it. In Chapter 8, Padovani describes the Hypha tool, which uses a type-based approach to check deadlock-freedom and lock-freedom of systems modelled in a form of pi-calculus. In Chapter 9, Garcia and Laneve present a tool for analysing deadlocks in Java programs; this tool, called JaDA, is based on a behavioural type system. The next three chapters report on projects that have added session types to functional programming languages in order to support typechecking of communication-based code. In Chapter 10, Orchard and Yoshida describe an implementation of session types in Haskell, and survey several approaches to typechecking the linearity conditions required for safe session implemen- tation. In Chapter 11, Melgratti and Padovani describe an implementation of session types in OCaml. Their system uses runtime linearity checking. In Chapter 12, Lindley and Morris describe an extension of the web programming language Links with session types; their work contrasts with the previous two chapters in being less constrained by an existing language design. Continuing the theme of session types in programming languages, the next two chapters describe two approaches based on Java. Hu’s work, presented in Chapter 13, starts with the Scribble description of a multiparty session type and generates an API in the form of a collection of Java classes, each class containing the communication methods that are available in a particular state of the protocol. Dardha et al., in Chapter 14, also start with a Scribble specification. Their StMungo tool generates an API as a single class with an associated typestate specification to constrain sequences of method calls. Code that uses the API can be checked for correctness with the Mungo typechecker. Finally, there are two chapters about programming with the MPI libraries. Chapter 15, by Ng and Yoshida, uses an extension of Scribble, called Pabble, to describe protocols that parametric in the number of runtime roles. From a Pabble specification they generate C code that uses MPI for communication and is guaranteed correct by construction. Chapter 16, by Ng et al., describes the ParTypes framework for analysing existing C+MPI programs with respect to protocols defined in an extension of Scribble. We hope that the book will serve a useful purpose as a report on the activities of COST Action IC1201 and as a survey of programming languages and tools based on behavioural types

Adaptive structured parallelism

Algorithmic skeletons abstract commonly-used patterns of parallel computation, communication, and interaction. Parallel programs are expressed by interweaving parameterised skeletons analogously to the way in which structured sequential programs are developed, using well-defined constructs. Skeletons provide top-down design composition and control inheritance throughout the program structure. Based on the algorithmic skeleton concept, structured parallelism provides a high-level parallel programming technique which allows the conceptual description of parallel programs whilst fostering platform independence and algorithm abstraction. By decoupling the algorithm specification from machine-dependent structural considerations, structured parallelism allows programmers to code programs regardless of how the computation and communications will be executed in the system platform.Meanwhile, large non-dedicated multiprocessing systems have long posed a challenge to known distributed systems programming techniques as a result of the inherent heterogeneity and dynamism of their resources. Scant research has been devoted to the use of structural information provided by skeletons in adaptively improving program performance, based on resource utilisation. This thesis presents a methodology to improve skeletal parallel programming in heterogeneous distributed systems by introducing adaptivity through resource awareness. As we hypothesise that a skeletal program should be able to adapt to the dynamic resource conditions over time using its structural forecasting information, we have developed ASPara: Adaptive Structured Parallelism. ASPara is a generic methodology to incorporate structural information at compilation into a parallel program, which will help it to adapt at execution

Symbolic play as a zone of proximal development: An analysis of informational exchange

Symbolic play has long been considered a beneficial context for development. According to Cultural Learning theory, one reason for this is that symbolically-infused dialogical interactions constitute a zone of proximal development. However, the dynamics of caregiver-child interactions during symbolic play are still not fully understood. In the current study, we investigated informational exchange between fifty-two 24-month-old infants and their primary caregivers during symbolic play and a comparable, non-symbolic, functional play context. We coded over 11,000 utterances for whether participants had superior, equivalent, or inferior knowledge concerning the current conversational topic. Results showed that children were significantly more knowledgeable speakers and recipients in symbolic play, whereas the opposite was the case for caregivers, who were more knowledgeable in functional play. The results suggest that, despite its potential conceptual complexity, symbolic play may scaffold development because it facilitates infants’ communicative success by promoting them to ‘co-constructors of meaning’

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