Proceedings of the 3rd Workshop on Domain-Specific Language Design and Implementation (DSLDI 2015)

The goal of the DSLDI workshop is to bring together researchers and practitioners interested in sharing ideas on how DSLs should be designed, implemented, supported by tools, and applied in realistic application contexts. We are both interested in discovering how already known domains such as graph processing or machine learning can be best supported by DSLs, but also in exploring new domains that could be targeted by DSLs. More generally, we are interested in building a community that can drive forward the development of modern DSLs. These informal post-proceedings contain the submitted talk abstracts to the 3rd DSLDI workshop (DSLDI'15), and a summary of the panel discussion on Language Composition

Computing infrastructure issues in distributed communications systems : a survey of operating system transport system architectures

The performance of distributed applications (such as file transfer, remote login, tele-conferencing, full-motion video, and scientific visualization) is influenced by several factors that interact in complex ways. In particular, application performance is significantly affected both by communication infrastructure factors and computing infrastructure factors. Several communication infrastructure factors include channel speed, bit-error rate, and congestion at intermediate switching nodes. Computing infrastructure factors include (among other things) both protocol processing activities (such as connection management, flow control, error detection, and retransmission) and general operating system factors (such as memory latency, CPU speed, interrupt and context switching overhead, process architecture, and message buffering). Due to a several orders of magnitude increase in network channel speed and an increase in application diversity, performance bottlenecks are shifting from the network factors to the transport system factors.This paper defines an abstraction called an "Operating System Transport System Architecture" (OSTSA) that is used to classify the major components and services in the computing infrastructure. End-to-end network protocols such as TCP, TP4, VMTP, XTP, and Delta-t typically run on general-purpose computers, where they utilize various operating system resources such as processors, virtual memory, and network controllers. The OSTSA provides services that integrate these resources to support distributed applications running on local and wide area networks.A taxonomy is presented to evaluate OSTSAs in terms of their support for protocol processing activities. We use this taxonomy to compare and contrast five general-purpose commercial and experimental operating systems including System V UNIX, BSD UNIX, the x-kernel, Choices, and Xinu

Efficient Software Implementation of Stream Programs

The way we use computers and mobile phones today requires large amounts of processing of data streams. Examples include digital signal processing for wireless transmission, audio and video coding for recording and watching videos, and noise reduction for the phone calls. These tasks can be performed by stream programs—computer programs that process streams of data. Stream programs can be composed of other stream programs. Components of a composition are connected in a network, i.e. the output streams of one component are sent as input streams to other components. The components, that perform the actual computation, are called kernels. They can be described in different styles and programming languages. There are also formal models for describing the kernels and the networks. One such model is the actor machine.This dissertation evaluates the actor machine, how it facilitates creating efficient software implementation of stream programs. The evaluation is divided into four aspects: (1) analyzability of its structure, (2) generality in what languages and styles it can express, (3) efficient implementation of kernels, and (4) efficient implementation of networks. This dissertation demonstrates all four aspects through implementation and evaluation of a stream program compiler based on actor machines

Modular and Safe Event-Driven Programming

Asynchronous event-driven systems are ubiquitous across domains such as device drivers, distributed systems, and robotics. These systems are notoriously hard to get right as the programmer needs to reason about numerous control paths resulting from the complex interleaving of events (or messages) and failures. Unsurprisingly, it is easy to introduce subtle errors while attempting to fill in gaps between high-level system specifications and their concrete implementations.This dissertation proposes new methods for programming safe event-driven asynchronous systems.In the first part of the thesis, we present ModP, a modular programming framework for compositional programming and testing of event-driven asynchronous systems.The ModP module system supports a novel theory of compositional refinement for assume-guarantee reasoning of dynamic event-driven asynchronous systems. We build a complex distributed systems software stack using ModP.Our results demonstrate that compositional reasoning can help scale model-checking (both explicit and symbolic) to large distributed systems.ModP is transforming the way asynchronous software is built at Microsoft and Amazon Web Services (AWS). Microsoft uses ModP for implementing safe device drivers and other software in the Windows kernel.AWS uses ModP for compositional model checking of complex distributed systems. While ModP simplifies analysis of such systems, the state space of industrial-scale systems remains extremely large.In the second part of this thesis, we present scalable verification and systematic testing approaches to further mitigate this state-space explosion problem.First, we introduce the concept of a delaying explorer to perform prioritized exploration of the behaviors of an asynchronous reactive program. A delaying explorer stratifies the search space using a custom strategy (tailored towards finding bugs faster), and a delay operation that allows deviation from that strategy. We show that prioritized search with a delaying explorer performs significantly better than existing approaches for finding bugs in asynchronous programs.Next, we consider the challenge of verifying time-synchronized systems; these are almost-synchronous systems as they are neither completely asynchronous nor synchronous.We introduce approximate synchrony, a sound and tunable abstraction for verification of almost-synchronous systems. We show how approximate synchrony can be used for verification of both time-synchronization protocols and applications running on top of them.Moreover, we show how approximate synchrony also provides a useful strategy to guide state-space exploration during model-checking.Using approximate synchrony and implementing it as a delaying explorer, we were able to verify the correctness of the IEEE 1588 distributed time-synchronization protocol and, in the process, uncovered a bug in the protocol that was well appreciated by the standards committee.In the final part of this thesis, we consider the challenge of programming a special class of event-driven asynchronous systems -- safe autonomous robotics systems.Our approach towards achieving assured autonomy for robotics systems consists of two parts: (1) a high-level programming language for implementing and validating the reactive robotics software stack; and (2) an integrated runtime assurance system to ensure that the assumptions used during design-time validation of the high-level software hold at runtime.Combining high-level programming language and model-checking with runtime assurance helps us bridge the gap between design-time software validation that makes assumptions about the untrusted components (e.g., low-level controllers), and the physical world, and the actual execution of the software on a real robotic platform in the physical world. We implemented our approach as DRONA, a programming framework for building safe robotics systems.We used DRONA for building a distributed mobile robotics system and deployed it on real drone platforms. Our results demonstrate that DRONA (with the runtime-assurance capabilities) enables programmers to build an autonomous robotics software stack with formal safety guarantees.To summarize, this thesis contributes new theory and tools to the areas of programming languages, verification, systematic testing, and runtime assurance for programming safe asynchronous event-driven across the domains of fault-tolerant distributed systems and safe autonomous robotics systems

Autonomous Machine을 위한 실시간 스트림 처리와 센서 퓨전을 지원하는 Splash 프로그래밍 언어의 설계

학위논문(박사)--서울대학교 대학원 :공과대학 전기·컴퓨터공학부,2020. 2. 홍성수.Autonomous machines have begun to be widely used in various application domains due to recent remarkable advances in machine intelligence. As these autonomous machines are equipped with diverse sensors, multicore processors and distributed computing nodes, the complexity of the underlying software platform is increasing at a rapid pace, overwhelming the developers with implementation details. This leads to a demand for a new programming framework that has an easy-to-use programming abstraction. In this thesis, we present a graphical programming framework named Splash that explicitly addresses the programming challenges that arise during the development of an autonomous machine. We set four design goals to solve the challenges. First, Splash should provide an easy-to-use, effective programming abstraction. Second, it must support real-time stream processing for deep-learning based machine learning intelligence. Third, it must provide programming support for real-time control system of autonomous machines such as sensor fusion and mode change. Finally, it should support performance optimization of software system running on a heterogeneous multicore distributed computing platform. Splash allows programmers to specify genuine, end-to-end timing constraints. Also, it provides a best-effort runtime system that tries to meet the annotated timing constraints and exception handling mechanisms to monitor the violation of such constraints. To implement these runtime mechanisms, Splash provides underlying timing semantics: (1) it provides an abstract global clock that is shared by machines in the distributed system and (2) it supports programmers to write birthmark on every stream data item. Splash offers a multithreaded process model to support concurrent programming. In the multithreaded process model, a programmer can write a multithreaded program using Splash threads we call sthreads. An sthread is a logical entity of independent execution. In addition, Splash provides a language construct named build unit that allows programmers to allocate sthreads to processes and threads of an underlying operating system. Splash provides three additional language semantics to support real-time stream processing and real-time control systems. First, it provides rate control semantics to solve uncontrolled jitter and an unbounded FIFO queue problem due to the variability in communication delay and execution time. Second, it supports fusion semantics to handle timing issues caused by asynchronous sensors in the system. Finally, it provides mode change semantics to meet varying requirements in the real-time control systems. In this paper, we describe each language semantics and runtime mechanism that realizes such semantics in detail. To show the utility of our framework, we have written a lane keeping assist system (LKAS) in Splash as an example. We evaluated rate control, sensor fusion, mode change and build unit-based allocation. First, using rate controller, the jitter was reduced from 30.61 milliseconds to 1.66 milliseconds. Also, average lateral deviation and heading angle is reduced from 0.180 meters to 0.016 meters and 0.043 rad to 0.008 rad, respectively. Second, we showed that the fusion operator works normally as intended, with a run-time overhead of only 7 microseconds on average. Third, the mode change mechanism operated correctly and incurred a run-time overhead of only 0.53 milliseconds. Finally, as we increased the number of build units from 1 to 8, the average end-to-end latency was increased from 75.79 microseconds to 2022.96 microseconds. These results show that the language semantics and runtime mechanisms proposed in this thesis are designed and implemented correctly, and Splash can be used to effectively develop applications for an autonomous machine.딥 러닝 기반 machine intelligence의 비약적인 발전으로 인해 autonomous machine들이 다양한 분야에서 활용되고 있다. 이런 기기들은 다양한 센서, 멀티코어 프로세서, 분산 컴퓨팅 노드를 장착하고 있기 때문에, 이들을 지원하기 위한 기반 소프트웨어 플랫폼의 복잡도는 빠른 속도로 증가하는 추세이다. 이에 따라 개발자들이 복잡한 소프트웨어 구조를 효과적으로 다룰 수 있도록 해주는 프로그래밍 프레임워크의 필요성이 대두되고 있다. 본 학위논문은 autonomous machine의 개발 과정에서 발생하는 문제들을 해결하기 위한 그래픽 기반 프로그래밍 프레임워크인 Splash를 제안한다. Splash라는 이름은 stream processing language for autonomous machine에서 앞의 세 단어의 첫 문자들을 따서 지어졌다. 이 이름은 물과 같이 흐르는 스트림 데이터를 다루기 위한 프로그래밍 언어와 런타임 시스템을 개발하겠다는 의도를 가진다. 본 논문에서는 복잡한 소프트웨어 구조를 효과적으로 다루기 위해 네 가지 디자인 목표를 설정한다. 첫째, Splash는 개발자에게 세부적인 구현 이슈를 숨기고, 쉽게 사용할 수 있는 프로그래밍 추상화를 제공하여야 한다. 둘째, Splash는 machine intelligence를 위한 실시간 스트림 처리를 지원할 수 있어야 한다. 셋째, Splash는 실시간 제어 시스템에서 널리 사용되는 센서 퓨전, 모드 변경, 예외 처리와 같은 기능들을 위한 지원을 제공하여야 한다. 넷째, Splash는 이기종 멀티코어 분산 컴퓨팅 플랫폼에서 수행되는 소프트웨어 시스템의 성능 최적화를 지원하여야 한다. Splash는 실시간 스트림 처리를 위해 개발자가 프로그램 상에 본질적인 end-to-end timing constraints를 명시할 수 있도록 한다. 그리고 개발자가 명시한 timing constraints를 인지하고 이를 최대한 지켜주는 best-effort 런타임 시스템과 timing constraints의 위반을 모니터링하고 처리해주는 예외 처리 메커니즘을 함께 제공한다. 이런 런타임 메커니즘들을 구현하기 위해 Splash는 두 가지 기본적인 timing semantics를 제공한다. 첫째, 분산 시스템 상에서 모든 머신들이 공유할 수 있는 global time base를 제공한다. 둘째, Splash 상에 들어오는 모든 스트림 데이터 아이템에 자신의 birthmark를 기록하도록 한다. Splash는 동시성 프로그래밍을 지원하기 위한 멀티 쓰레디드 처리 모델을 제공한다. Splash 프로그래머는 sthread라는 논리적인 수행 단위를 사용하여 프로그램을 개발할 수 있다. 그리고 Splash는 sthread들을 실제 운영체제의 수행 단위인 프로세스와 쓰레드에게 할당하는 과정을 돕기 위한 빌드 유닛이라는 language construct를 제공한다. Splash는 timing semantics와 멀티 쓰레디드 처리 모델을 기반으로 실시간 스트림 처리와 실시간 제어 시스템을 지원하기 위한 세 가지 language semantics를 추가로 지원한다. 첫째는 스트림 데이터의 통신이나 처리 지연으로 인해 발생하는 지터나 바운드 되지 않는 큐 문제를 해결하기 위한 rate 제어 semantics이다. 둘째는 센서 퓨전 과정에서 시간적으로 동기화되지 않은 센서 입력들로 인한 타이밍 이슈들을 해결하기 위한 퓨전 semantics이다. 마지막은 가변적인 제어 시스템의 요구사항을 충족시키기 위해 수행 로직의 변경을 지원하는 모드 변경 semantics이다. 본 논문에서는 각각의 language semantics를 구체적으로 설명하고, 이를 실현하기 위한 런타임 메커니즘을 설계하고 구현한다. Splash의 효용성을 검증하기 위해서, 본 논문은 Splash를 사용하여 LKAS 응용을 개발하고 이를 Splash 런타임 시스템 상에서 수행시키며 실험을 진행하였다. 본 논문에서는 rate 제어 메커니즘, 센서 퓨전 메커니즘, 모드 변경 메커니즘, 빌드 유닛 기반 allocation을 각각 선정된 성능 지표들을 사용하여 검증하였다. 첫째, Splash의 rate 제어기를 사용하면 지터가 30.61ms에서 1.66ms로 감소되었고, 이로 인해 주행 차량의 측면 편차와 방향각이 각각 0.180m에서 0.016m, 0.043rad에서 0.008rad으로 개선된다는 것을 확인하였다. 둘째, 센서 퓨전을 위해 제안된 퓨전 연산자가 설계된 의도대로 정상 동작하고, 평균 7us의 낮은 오버헤드만을 유발한다는 것을 확인하였다. 셋째, 모드 변경 기능의 정상 동작을 검증하였고 그 과정에서 발생하는 시간적 오버헤드는 평균 0.53ms에 불과하였다. 마지막으로, synthetic workload에 대해 컴포넌트들에 매핑된 빌드 유닛 개수를 1개, 2개, 4개, 8개로 증가시킴에 따라 평균 end-to-end 지연 시간은 75.79us, 330.80us, 591.87us, 2022.96us로 증가하는 것을 확인하였다. 이러한 결과들은 본 논문에서 제안하는 language semantics와 런타임 메커니즘들이 의도대로 설계, 구현되었고, 이를 통해 autonomous machine의 응용들을 효과적으로 개발할 수 있다는 것을 보여준다.Chapter 1 Introduction p.1 1.1 Motivation p.2 1.2 Splash Overview p.5 1.3 Organization of This Dissertation p.9 Chapter 2 Related Work p.10 2.1 Kahn Process Network p.10 2.2 Firing Rule Applied to a Process p.13 2.3 Programming Framework for an Autonomous Machine p.14 2.4 Runtime Software for an Autonomous Machine p.16 2.5 Rate Control p.18 2.5.1 Traffic Shaping p.20 2.5.2 Traffic Policing p.22 2.6 Sensor Fusion p.23 2.6.1 Measurement Fusion p.24 2.6.2 Situation Fusion p.27 2.7 Mode Change p.30 2.7.1 Synchronous Mode Change p.32 2.7.2 Asynchronous Mode Change p.32 Chapter 3 Motivation and Contributions p.34 3.1 Problem Description p.34 3.2 Limitations of Kahn Process Network p.36 3.3 Contributions of this Dissertation p.38 Chapter 4 Underlying Timing Semantics of Splash p.41 4.1 End-to-End Timing Constraints p.41 4.2 Global Time Base and In-order Delivery p.42 4.3 Integrating Three Distinct Computing Models p.43 Chapter 5 Splash Language Constructs p.45 5.1 Processing Component p.46 5.2 Port p.49 5.3 Channel and Clink p.52 5.4 Fusion Operator p.54 5.5 Factory and Mode Change p.60 5.6 Build Unit p.65 5.7 Exception Handling p.67 Chapter 6 Splash Runtime Mechanisms p.69 6.1 Rate Control Mechanism p.69 6.2 Sensor Fusion Mechanism p.70 6.3 Mode Change Mechanism p.77 Chapter 7 Code Generation and Runtime System p.80 7.1 Build Unit-based Allocation p.80 7.2 Code Generation Template p.82 7.3 Splash Runtime System p.84 Chapter 8 Experimental Evaluation p.86 8.1 LKAS Program p.86 8.2 Experimental Environment p.91 8.3 Evaluating Rate Control p.92 8.4 Evaluating Sensor Fusion p.96 8.5 Evaluating Mode Change p.97 8.6 Evaluating Build Unit-based Allocation p.99 Chapter 9 Conclusion p.102 Bibliography p.104 Abstract in Korean p.113Docto

A Static Analyzer for Large Safety-Critical Software

We show that abstract interpretation-based static program analysis can be made efficient and precise enough to formally verify a class of properties for a family of large programs with few or no false alarms. This is achieved by refinement of a general purpose static analyzer and later adaptation to particular programs of the family by the end-user through parametrization. This is applied to the proof of soundness of data manipulation operations at the machine level for periodic synchronous safety critical embedded software. The main novelties are the design principle of static analyzers by refinement and adaptation through parametrization, the symbolic manipulation of expressions to improve the precision of abstract transfer functions, the octagon, ellipsoid, and decision tree abstract domains, all with sound handling of rounding errors in floating point computations, widening strategies (with thresholds, delayed) and the automatic determination of the parameters (parametrized packing)