To achieve good performance in systems with limited computer resources, the constraints of the implementation platform must be taken into account at design time. To facilitate this, software tools are needed to analyze and simulate how timing affects control performance. This article describes two such tools: Jitterbug and TrueTime.

/pdf/how-does-control-timing-affect-performance-analysis-and-2ic4oksu1m.pdf

How does control timing affect performance? Analysis and simulation of timing using Jitterbug and TrueTime

We advocate a novel approach to grid computing that is based on a combination of "classic" operating system level virtual machines (VMs) and middleware mechanisms to manage VMs in a distributed environment. The abstraction is that of dynamically instantiated and mobile VMs that are a combination of traditional OS processes (the VM monitors) and files (the VM state). We give qualitative arguments that justify our approach in terms of security, isolation, customization, legacy support and resource control, and we show quantitative results that demonstrate the feasibility of our approach front a performance perspective. Finally, we describe the middleware challenges implied by the approach and an architecture for grid computing using virtual machines.

/pdf/a-case-for-grid-computing-on-virtual-machines-4wt56nffgw.pdf

A case for grid computing on virtual machines

Now that the use of garbage collection in languages like Java is becoming widely accepted due to the safety and software engineering benefits it provides, there is significant interest in applying garbage collection to hard real-time systems. Past approaches have generally suffered from one of two major flaws: either they were not provably real-time, or they imposed large space overheads to meet the real-time bounds. We present a mostly non-moving, dynamically defragmenting collector that overcomes both of these limitations: by avoiding copying in most cases, space requirements are kept low; and by fully incrementalizing the collector we are able to meet real-time bounds. We implemented our algorithm in the Jikes RVM and show that at real-time resolution we are able to obtain mutator utilization rates of 45% with only 1.6--2.5 times the actual space required by the application, a factor of 4 improvement in utilization over the best previously published results. Defragmentation causes no more than 4% of the traced data to be copied.

/pdf/a-real-time-garbage-collector-with-low-overhead-and-2wvfltzccw.pdf

A real-time garbage collector with low overhead and consistent utilization

Message-based communication offers the potential benefits of providing stronger specification and cleaner separation between components. Compared with shared-memory interactions, message passing has the potential disadvantages of more expensive data exchange (no direct sharing) and more complicated programming.In this paper we report on the language, verification, and run-time system features that make messages practical as the sole means of communication between processes in the Singularity operating system. We show that using advanced programming language and verification techniques, it is possible to provide and enforce strong system-wide invariants that enable efficient communication and low-overhead software-based process isolation. Furthermore, specifications on communication channels help in detecting programmer mistakes early---namely at compile-time---thereby reducing the difficulty of the message-based programming model.The paper describes our communication invariants, the language and verification features that support them, as well as implementation details of the infrastructure. A number of benchmarks show the competitiveness of this approach.

/pdf/language-support-for-fast-and-reliable-message-based-28wbpv35gt.pdf

Language support for fast and reliable message-based communication in singularity OS

Ownership types provide a statically enforceable notion of object-level encapsulation. We extend ownership types with computational effects to support reasoning about object-oriented programs. The ensuing system provides both access control and effects reporting. Based on this type system, we codify two formal systems for reasoning about aliasing and the disjointness of computational effects. The first can be used to prove that evaluation of two expressions will never lead to aliases, while the latter can be used to show the non-interference of two expressions.

Ownership, encapsulation and the disjointness of type and effect

New languages, programming disciplines, operating systems, and software engineering techniques sometimes hold considerable potential for real-time software developers. A promising area of interest-but one fairly new to the real-time community-is object-oriented programming. Java, for example, draws heavily from object orientation and is highly suitable for extension to real-time and embedded systems. Recognizing this fit between Java and real-time software development, the Real-Time for Java Experts Group (RTJEG) began developing the real-time specification for Java (RTSJ) in March 1999 under the Java Community Process. This article explains RTSJ's features and the thinking behind the specification's design. The goal of the RTJEG, of which the authors are both members, was to provide a platform-a Java execution environment and application program interface (API)-that lets programmers correctly reason about the temporal behavior of executing software.

https://database.sarang.net/study/java/rtj/rtj.pdf

G. Bollella

Papers

The Real-Time Specification for Java