Two Alternative RMI Models for Real-Time Distributed Applications

Resource management policies for real-time Java remote invocations

Region-Based RTSJ Memory Management: State of the art

This paper illustrates how the real-time specification for Java (RTSJ) can be modified to allow applications to implement more flexible scheduling. The proposed approach is a two-level scheduling mechanism where the first level is the RTSJ priority scheduler and the second level is under application control. Minimum, backward-compatible changes to the RTSJ specification are discussed to motivate the required interface. The only assumptions made about the underlying real-time operating system are that it supports pre-emptive priority-based dispatching and that changes to priorities have immediate effect.

SummaryThis paper proposes a web‐based interactive workflow definition and invocation system assisting users in orchestrating a set of distributed services‐activities and expressing complex dependencies between them in XML. We use Ant, which is a Java‐based and freely distributed commodity tool, for workflow definitions and workflow engine. Adopting Ant as a workflow engine provides platform independence and immediate integration into the Grid services framework. Sometimes, workflow scripts need to be used repeatedly with a little change; framework enables reusable scripts to be created, stored and edited for later use. This allows sharing and dynamic modifications of workflows between multiple participants. The practicality and usefulness of the system is demonstrated through a concrete case study on Remote Method Invocation (RMI) jobs. Copyright © 2014 John Wiley & Sons, Ltd.

The OSGi Framework, has proven ideal in developing dynamically reconfigurable Java applications based on the principles of Component-Based Software Engineering (CBSE) and Service-Oriented Architecture (SOA). One domain where OSGi has yet to make an impact is real-time systems. This is partly due to the fact that the OSGi Framework is based on standard Java, which is not suitable for developing such systems. Other reasons include the absence of various features such as temporal isolation, admission control, and a reconfigurable garbage collector (along with the associated analysis to determine the pace of garbage collection). Also, a number of features of the OSGi Framework increase the difficulty in determining the worst case execution time (WCET) of threads. This makes real-time analysis more difficult. This chapter discusses the problems associated with extending the OSGi Framework and integrating it with the Real-Time Specification for Java (RTSJ). The focus is on the design of a real-time version of the OSGi Framework (RT-OSGi) which is capable of deploying dynamically reconfigurable real-time Java applications.

The Real-Time Specification for Java (RTSJ) [13] is becoming a popular choice in the world of real-time and embedded programming. However, RTSJ introduces many non-intuitive rules and restrictions which prevent its wide adoption. Moreover, current state-of-the-art frameworks usually fail to alleviate the development process into higher layers of the software development life-cycle. In this paper we extend our philosophy that RTSJ concepts need to be considered at early stages of software development, postulated in our prior work [2], in a framework that provides continuum between the design and implementation process. A component model designed specially for RTSJ serves here as a cornerstone. As the first contribution of this work, we propose a development process where RTSJ concepts are manipulated independently of functional aspects. Second, we mitigate complexities of RTSJ-development by automatically generating execution infrastructure where real-time concerns are transparently managed. We thus allow developers to create systems for variously constrained real-time and embedded environments. Performed benchmarks show that the overhead of the framework is minimal in comparison to manually written object-oriented applications, while providing more extensive functionality. Finally, the framework is designed with the stress on dynamic adaptability of target systems, a property we envisage as a fundamental in an upcoming era of massively developed real-time systems.

The paper presents a middleware implemented in Java, RT-MED, which corresponds to a software layer to be placed above the operating system. This software component is designed to execute and evaluate the performance, reliability and correctness of some real-time scheduling approaches which are theoretically validated. It describes a transition from the theory to the actual implementation of the proposed solutions. These solutions are based on a combinatorial optimization approach to solve the problem of feasibility in a system which is dynamically reconfigurable. RT-MED also presents a patch between the system and its environment under different constraints such as time and energy. It offers a set of adjustable parameters to control the flow of the execution. The middleware can be integrated into many operating systems and provides good quality both in terms of execution time and energy consumption. The implementation of this tool is based on java technology with embedded and real-time systems supported by the Real-Time Specification for Java. We have used a UML profile to describe various states and run-time reconfiguration of the embedded system. Results show that the middleware can effectively maintain the control and the stability of the system.

Real-time systems are notoriously difficult to design and implement, and, as many real-time problems are safety-critical, their solutions must be reliable as well as efficient and correct. While higher-level programming models (such as the Real-Time Specification for Java) permit real-time programmers to use language features that most programmers take for granted (objects, type checking, dynamic dispatch, and memory safety) the compromises required for real-time execution, especially concerning memory allocation, can create as many problems as they solve. This paper presents Scoped Types and Aspects for Real-Time Systems (STARS) a novel programming model for real-time systems. Scoped Types give programmers a clear model of their programs’ memory use, and, being statically checkable, prevent the run-time memory errors that bedevil the RTSJ. Adopting the integrated Scoped Types and Aspects approach can significantly improve both the quality and performance of a real-time Java systems, resulting in simpler systems that are reliable, efficient, and correct.

The goal of this paper is to evaluate the real-time specification for Java proposal by performing several case studies. These case studies include: an extensible general resource controller; atomic action support infrastructure; unbounded and imprecise computations. They have been used previously by the Ada community to evaluate the efficacy of the Ada concurrency and real-time models. Our results indicate that the Real-Time Specification for Java is expressive enough to cope with the demands of real-time concurrent programming. If it can be implemented efficiently, it will provide an alternative to Ada 95 for programming real-time systems.

[Abstract] The Operationally Responsive Spa ce (ORS) program envisions building a 6 day to support fast changing tactical missions. A key requirement would be the ability to rapidly compose the spacecraft that would perform both the needed mission - and spacecraft -oriented functionality using (PnP) enabled spacecraft components. To address this need, a service -oriented spacecraft architectural model is under development as part of the Air Force Research Laboratory (AFRL) Responsive Space Testbed effort to provide a reusable , reference infrastructure for Responsive Space. The Lockheed Martin ATC is pursuing the development of a Java -based distributed architecture environment that supports this service -oriented, reference spacecraft architectural model. A key component of th is approach involves a simulation architecture that is based on spacecraft services, much like the service -oriented models now widely used in the consumer marketplace, but is an evolutionary step to extend simulation to operations. To span the entire range from simulation to operations seamlessly, a single vertically integrated software architecture is needed. The Java -based distributed architecture provides such an environment with its evolution from desktop, to enterprise, to mobile devices, and now to real time systems. The Java environment addresses the complexity needed for operational simulations and ultimate deployment for integrated spacecraft flight and payload control systems. The Real Time Specification for Java (RTSJ) supports hard real time, s oft real time and non -real time processes all interoperating within the same virtual machine. Initial prototyping is being done using IBM's Real Time Java (RTJ) implementation of the RTSJ. The Java platform support several libraries, and one in particular, the JINI protocol, which supports the operation of dynamically changing networks of distributed services (and devices). Using JINI, running as a non -real time process within IBM's RTJ environment, provides the rich set of Plug -N-Play capabilities needed to demonstrate both automatic configuration, as would be needed for Assembly, Integration and Test (AI&T), as well as for operational fault tolerance and reconfigurability needed for on -orbit operations.

: There is an increasing interest in recent years to use the Java(trade mark) programming language for implementing real-time systems. Recent advances in the Real-Time Specification for Java (RTSJ) have resulted in the introduction of new means for creating predictable real-time environments for Java programs. However, these new features also make the Java semantics more complex and the run-time behaviors of the Java programs more difficult to analyze. In this technical report, we describe a number of preliminary experiments we performed to study the features of the Sun Java Real-Time System (RTJ 1.0). We designed these experiments to verify the viability of the Real-Time Java language for the implementation of the Global Integrated Fire Control System (GIFC)-a component of the C2BMC element of the Ballistic Missile Defense System (BMDS). Our preliminary experiment shows that it is preferable to use only the Real-Time Java threads that use the heap memory and not the no-heap real-time threads for the GIFC software. However, such architecture cannot be implemented by using RTJ 1.0. Further experiments are needed to determine if the preferred architecture can be implemented with the upcoming RTJ 2.0, which will give programmers more control over the priority of the garbage collection.

The Real-Time Specification for Java (RTSJ) supports concurrency mainly by using object-oriented mechanisms. Hence it entangles with functional components. This crosscutting nature does not promote coherence and traceability between real-time systems requirement specifications, designs, and implementations. Such qualities are only possible by separating it. We show how to separate concurrency, a non-functional concern, from thread-safe functional concerns using “aspectisation”. The paper’s contributions are in devising a systematic separation approach, and elaboration of challenges and requirements for “pluggable” concurrency.KeywordsConcurrencyAspect-OrientationObject-Orientation

Planetary science missions, such as those that explore Mars and Saturn, employ a variety of spacecraft such as arbiters, landers, probes, and rovers. Each of these kinds of spacecraft depends on embedded real-time control systems - systems that are increasingly being asked to do more as challenging new mission concepts are proposed. For both systems engineers and software engineers the large challenges are in analysis, design and verification of complex control systems that run on relatively limited processors. Project Golden Gate - a collaboration among NASA's Jet Propulsion Laboratory, Sun Microsystems Laboratory, and Carnegie Mellon University - is exploring those challenges in the context of real-time Java applied to space mission software. This paper describes the problem domain and our experimentation with the first commercial implementation of the real time specification for Java. The two main issues explored in this report are: (I) the effect of RTSJ's nonheap memory on the programming model, and (2) performance benchmarking of RTSJ/Linux relative to C++/VxWorks

Over 90 percent of all microprocessors are now used for real-time and embedded applications, and the behavior of many of these applications is constrained by the physical world. Higher-level programming languages and middleware are needed to robustly and productively design, implement, compose, integrate, validate, and enforce real-time constraints along with conventional functional requirements and reusable components. Designing real-time and embedded systems that implement their required capabilities, are dependable and predictable, and are parsimonious in their use of limited computing resources is hard; building them on time and within budget is even harder. Moreover, due to global competition for market share and engineering talent, companies are now also faced with the problem of developing and delivering new products in short time frames. Therefore it is essential that the production of real-time embedded systems can take advantage of languages, tools, and methods that enable higher software productivity. Ideally, developers should use a programming language that shields them from many accidental complexities, such as type errors, memory management, and steep learning curves. The Java programming language has become an attractive choice because of its safety, productivity,its relatively low maintenance costs, and the availability of well trained developers. Although it has good software engineering characteristics, Java is unsuitable for developing real-time embedded systems, mainly due to under-specification of thread scheduling and the presence of garbage collection. Recently, to address these problems, a number of extensions to Java have been proposed by the Java Community Process Expert Group for the Real-Time Specification for Java (RTSJ) among others. The intent of these specifications is the development of real-time applications by providing several additions such as extending the Java memory model, providing stronger semantics in thread scheduling, and so on. Interest in real-time Java in both the research community and industry, because of its challenges and its potential impact on the development of embedded and real-time applications, has recently increased, significantly. This interest in the industry comes not only from traditional applications, such as industrial control, but also for business and financial applications. The goal of the proposed workshop is to gather researchers working on real-time and embedded Java to identify the challenging problems that still need to be properly resolved in order to assure the success of the of real-time Java as a technology, and to report results and experience gained by researchers.

: This research is directed towards the implementation of a comprehensive toolkit for the development and verification of high assurance reactive systems, especially concurrent, real time, and hybrid systems. For this, we have designed and implemented the STeP (Stanford Temporal Prover) verification system. STeP is a tool for the computer aided formal verification of reactive systems, including real time and hybrid systems based on their temporal specification. STeP integrates model checking and deductive methods to allow the verification of a broad class of systems, including parameterized (N component) circuit designs, parameterized (N process) programs. and programs with infinite data domains.