Resource management policies for real-time Java remote invocations

Java's popularity, facilities and platform independence have made it an interesting language for the real time community. The RTSJ (real-time specification for Java) is a Java extension to allow the development of real-time systems. RTSJ does not supply any support for the development of real-time distributed systems. The goal of this work is to define support for this type of systems, based on RMI (remote method invocation). However, the high diversity of real-time systems implies that there is not a single RT-RMI definition that satisfies their requirements. This article presents the basics of two real-time RMI approaches: safety critical RMI, to support hard real-time and high integrity requirements, and quality of service RMI for soft real-time systems, which is based on resource reservation to provide some minimal required quality.

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.

The paper addresses the issue of improving the performance of memory management for real time Java applications, building upon the Real-Time Specification for Java (RTSJ) from the Real-Time Java Expert Group. In a first step, a thorough analysis of the parameters influencing the performance of memory management together with ways of improvement are presented. The implementation of a memory management solution, which is compliant with the RTSJ and integrating the proposed improvements is then sketched.

[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.

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

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.

: 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.

This paper presents some of the issues related to the use of multi-core architectures for real-time systems, in particular for real-time Java. Currently, the Real-Time Specification for Java (RTSJ) does not account for aspects of parallel computing, but the widespread use of multi-core architectures advocates for the need of a change in this regard. Some of these aspects relate closely to architectural features that need to be properly exported to the application level. We discuss the impact of multi-core processors, both symmetric and asymmetric, on process/thread scheduling. We also analyze the changes needed for some of the important features of RTSJ, such as the priority inversion avoidance, in the new context of multi-core processing. Also, locking and fairness issues are discussed with respect to the use of multi-core processors for real-time Java.

Next generation applications will demand more cost-effective programming abstractions to reduce increasing maintenance and development costs. In this context, the article explores the integration of an efficient programming language and high-level real-time programming abstractions. The resulting abstraction is called Embedded Cyber Physical C (ECP-C) and it is useful for designing real-time applications directly on C. The abstraction has its roots on the real-time Java: one of the most modern programming languages, which benefited from mature programming patterns previously developed for other languages. It also targets embedded processors running on limited hardware. ECP-C takes the programming abstractions described in real-time Java and reflects them into a C application system, providing extensions for multi-threading, resource sharing, memory management, external event, signaling, and memory access. It also reports on the performance results obtained in a set of infrastructures used to check ECP-C, providing clues on the overhead introduced by these mechanisms on limited infrastructures.

Region-Based RTSJ Memory Management: State of the art

A simple but effective optimisation for a popular level‐5 protocol called Java's Remote Method Protocol, which is used in a distribution model named RMI (Java's Remote Method Invocation) is presented. The protocol has been enhanced with a simple multiplexing mechanism which offers the possibility of transferring several parallel request–response interactions without opening new transfer control protocol/Internet protocol connections. The temporal overhead and the advantages stemmed from the approach in terms of response‐time are explored in a simple but realistic evaluation scenario: a local area network (LAN) (switched‐Ethernet) infrastructure under the small packet size condition (i.e. when the remote invocation does not have packet fragmentation). Presented results show that the proposed extensions are useful in the LAN scenario under the non‐fragmentation assumption in applications that do not require packet fragmentation.

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.

We propose a new, minimal specification for real-time Java for safety critical applications. The intention is to provide a profile that supports programming of applications that can be validated against safety critical standards such as DO-178B (1992). The proposed profile is in line with the Java specification request JSR-302: Safety Critical Java Technology, which is still under discussion. In contrast to the current direction of the expert group for the JSR-302 we do not subset the rather complex Real-Time Specification for Java (RTSJ). Nevertheless, our profile can be implemented on top of an RTSJ compliant JVM

Fine-Grained Parallel and Distributed Spatial Stochastic Simulation of Biological Reactions

(ProQuest: ... denotes formulae omitted.)1 Research Premises and HypothesisMaintenance costs have a consistent weight in the total costs generated by an application during its entire lifecycle. Previously conducted research and studies that focus on software maintenance support this claim. In [2], the 60/60 rule of software is depicted. The rule claims that maintenance accounts for 60% of the total costs generated by a software in its entire lifecycle. Enhancement or perfective [3] maintenance tasks account for 60% of all the costs generated by maintenance [2], whereas error correction or corrective [3] maintenance tasks account only for 17% of total maintenance costs [2]. In [4] it's stated that software applications evolve over time to meet the changing needs which leads to maintenance generating 67% of the applications total lifecycle costs. In [5] it is argued that maintenance typically accounts for 75% or more of the total software workload. Other relevant research place maintenance costs at 90% [6], 75% [7], 90% [8] or at 60% to 70% [9] of the overall application's lifecycle cost. It is therefore of paramount importance to accurately estimate maintenance cost before implementing a software project in order to better comprehend the total costs associated with developing and owing a software application. Better understanding maintenance costs will provide valuable information regarding resource planning and the appropriate time to decommission the application.The cost of maintenance is directly determined by the number of people involved in the maintenance process and the number of hours each person invests in the maintenance tasks. Thus in order to estimate maintenance cost one needs to estimate the effort invested in the maintenance process. The maintenance effort is expressed in man-hours which entails the number of ours dedicated by the maintenance team to implementing maintenance tasks. Maintenance in web applications has two main components: content maintenance and technical maintenance.Content maintenance requires performing tasks of a non-technical nature like updating product inventory and information, adding news or articles, managing blog posts, updating contact or brand and visual identity information and moderating user comments or messages. Content maintenance team staffing and therefore content maintenance effort is determined by the web application's size [1].According to [1] and as presented in Table 1, content maintenance cost is determined by the number of hours required to keep the web application up to date in terms of content. The larger the application the more hours need to be invested in keeping it up to date in terms of content. The more content changes in an application the more technical maintenance tasks are generated. Technical maintenance tasks are generated because content managers spot bugs or request new functionality to help keep the content up to date. Therefore, content update frequency is a factor that impacts maintenance effort and cost.Technical maintenance requires adding new functionality, performing regular back-ups, monitoring website outages, checking IP reputation, checking DNS configuration, test website speed, check for broken links, perform software updates if third party software was used when developing the web application, monitor traffic statistics and review search engine indexing.According to [1] and as presented in Table 2, technical team stuffing is determined by the level of complexity built into the web application. Thus, a Basic web application which is characterized by static content build mainly using front-end technologies like HTML, CSS and JavaScript will require no more than 1 person to perform maintenance tasks. A Dynamic web application which stores its content in a database and has functionality which is powered by PHP, Java, ASP.NET, Python, Ruby or any other high-level programming language will require 1 to 2 persons to perform maintenance tasks. …