Experiments with the Sun Java Real-Time System--Part 2

2005

The embedded real-time development community is investigating different approaches in order to provide modularity and reuse features for system design in this area, as well as a more appropriate mapping technique between requirements and implementation. The Java technology is very promising for this community, mainly after the research efforts on its real-time extension RTSJ-real-time specification for Java. However, there are still some critic factors related to the adoption of Java for real-time applications, and some of them deserve special attention. This paper reports a study of some of these decisive factors, such as the choice of the underlying operating system, the use of a middleware (virtual machine) or a native code, and the use of the Java real-time API (RTSJ)

Object-Oriented Real-Time Distributed Computing, 2003

The run-time characteristics of Java, such as high frequency of method invocation, dynamic dispatching and dynamic load- ing, make Java more difficult than other object-oriented pro- gramming languages, such as C++, for conducting Worst-Case Execution Time (WCET) analysis. To offer a more flexible way to develop object-oriented real-time applications in the real- time Java environment without loss of predicability and

Microprocessors and Microsystems, 2018

SystemJ is a programming language based on the Globally Asynchronous Locally Synchronous (GALS) Model of Computation (MoC) used to design safety critical hard real-time systems. SystemJ uses the Java programming language as the "host" language, for carrying out data computations, because Java provides clearly defined operational semantics, type and memory safety in the form of the Garbage Collector (GC), which help with formal functional verification. The same GC, which helps in functional verification, makes Worst Case Reaction Time (WCRT) 1 analysis challenging. Any WCRT analysis framework for GALS programs needs to consider the operations performed by the host language. It has been shown that the worst case time estimates for garbage collection cycles are in seconds, whereas the program's WCRT itself is in micro-seconds. These pessimistic estimates render the WCRT analysis framework ineffective. In order to overcome this problem, we develop a compiler assisted memory management technique for applications written in SystemJ. The SystemJ MoC plays the central role in the proposed technique. The SystemJ MoC allows clearly demarcating the state boundaries of the program, which in turn allows us to partition the heap, at compile time, into two distinct areas: (1) the memory area called the permanent heap , which holds objects that are alive throughout the life time of the application, and (2) the memory area used to hold all other objects, called the transient heap. The size of these memory areas are bounded statically. Furthermore, the memory allocation and reclaim procedures are simple load and pointer reset operations, respectively, which are guaranteed to complete within a bounded number of clock-cycles, thereby alleviating the need for large pessimistic WCRT bounds obtained due to the GC. Experimental results also show that the proposed approach is approximately three times faster, in terms of memory allocation times as compared to standard real-time GC approaches.

Companion of the 18th annual ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications - OOPSLA '03, 2003

The Real-Time Specification for Java (RTSJ) provides facilities for deterministic, real-time execution in a language that is otherwise subject to variable latencies in memory allocation and garbage collection. A major consequence of these facilities is that the normal Java practice of passing around references to objects in heap memory cannot be used in hard real-time activities. Instead, designers must think carefully about what type of non-heap memory to use and how to transfer data between components without violating RTSJ's memory-area assignment rules. This report explores the issues of programming with non-heap memory from a practitioner's view in designing and programming realtime control loops using a commercially available implementation of the RTSJ.

2002

The Java language has several attractive features but cannot at present be used in on-board systems primarily because it lacks support for hard real-time operation. This shortcoming is in being addressed: some suppliers are already providing implementations of Java that are RTcompliant; Sun Microsystem has approved a formal specification for a real-time extension of the language; and an independent consortium is working on an alternative specification for real-time Java. It is therefore expected that, within a year or so, standardized commercial implementations of real-time Java will be on the market. Availability of real-time implementations now opens the way to its use on-board. Within this context, this paper has two objectives. Firstly, it discusses the suitability of Java for on-board applications. Secondly, it reports the results of an ESA study to port a software framework for on-board control systems to a commercial real-time version of Java.

Object-Oriented Real-Time Distributed Computing, 2002

This paper presents a real-time Java hardware and soft- ware system for use in embedded applications. The system includes a multithreaded Java microcontroller, an adapted Java Virtual Machine (JVM) and an extended Application Programming Interface (API). The microcontroller core is designed with a multithreaded pipeline and hardware sup- port for real-time scheduling algorithms. The Java Virtual Machine consists of trap

Real-Time Systems, 2000

This paper addresses the issue of improving the performance of memory management for real-time Java applications, building upon the real-time speci®cation for Java (RTSJ) from the Real-Time Java Expert Group. In a ®rst step, a collecting dynamic memory solution including both a real-time garbage collector and region-based memory management, is proposed. A thorough analysis of the parameters in¯uencing the performance of write barriers in memory management, together with ways of improvement are then presented. Finally, the implementation of a memory management solution compliant with the RTSJ and integrating the proposed improvements is sketched.

11th IEEE Symposium on …, 2008

2002

The Distributed Real-Time Specification for Java (DRTSJ) is under development within Sun's Java Community Process (JCP) as Java Specification Request 50 (JSR-50), lead by the MITRE Corporation. We present the engineering considerations and design decisions settled by the Expert Group, the current and proposed form of the Reference Implementation, and a summary of open issues. In particular, we present an approach to integrating the distributable threads programming model with the Real-Time Specification for Java and discuss the ramifications for composing distributed, real-time systems in Java. The Expert Group plans to release an initial Early Draft Review (EDR) for previewing the distributable threads abstraction in the coming months, which we describe in detail. Along with that EDR, we will make available a demonstration application from Virginia Tech, and a DRTSJ-compatible RTSJ VM from Apogee.

Real-Time Systems, 2007

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.