Exception Handling in the Choices Operating System

Abstract. Exception handling is a powerful abstraction that can be used to help manage errors and support the construction of reliable operating systems. Using exceptions to notify system components about exceptional conditions also reduces coupling of error handling code and increases the modularity of the system. We explore the benefits of incorporating exception handling into the Choices operating system in order to improve reliability. We extend the set of exceptional error conditions in the kernel to include critical kernel errors such as invalid memory access and undefined instructions by wrapping them with language-based software exceptions. This allows developers to handle both hardware and software exceptions in a simple and unified manner through the use of an exception hierarchy. We also describe a catch-rethrow approach for exception propagation across protection domains. When an exception is caught by the system, generic recovery techniques like policy-driven micro-reboots and restartable processes are applied, thus increasing the reliability of the system.

Design and performance of MPEG video streaming to palmtop computers

Today's wide variety of computing devices oer a large range of resource availability. These resources include CPU speed, bandwidth, and memory. Workstations and PCs typically are rich in resources, whereas palmtop devices are generally quite limited. This disparity oers challenges to integrating these heterogeneous devices into a single distributed system. Services must be available to each device, but it may be necessary to modify certain services if the connected device does not have the required resources to support them. Proxies may be introduced into the system to o-load computations that would preclude certain services to resource-deprived devices. We have implemented one such proxy that enables the viewing of live MPEG video on the 3Com PalmPilot. The proxy is able to transform the video feed on-the-y, removing extraneous information, thereby reducing CPU and memory requirements and allowing palm devices to participate in video sessions. This paper discusses the design and p..

InvertNet: a new paradigm for digital access to invertebrate collections

InvertNet, one of the three Thematic Collection Networks (TCNs) funded in the first round of the U.S. National Science Foundation’s Advancing Digitization of Biological Collections (ADBC) program, is tasked with providing digital access to ~60 million specimens housed in 22 arthropod (primarily insect) collections at institutions distributed throughout the upper midwestern USA. The traditional workflow for insect collection digitization involves manually keying information from specimen labels into a database and attaching a unique identifier label to each specimen. This remains the dominant paradigm, despite some recent attempts to automate various steps in the process using more advanced technologies. InvertNet aims to develop improved semi-automated, high-throughput workflows for digitizing and providing access to invertebrate collections that balance the need for speed and cost-effectiveness with long-term preservation of specimens and accuracy of data capture. The proposed workflows build on recent methods for digitizing and providing access to high-quality images of multiple specimens (e.g., entire drawers of pinned insects) simultaneously. Limitations of previous approaches are discussed and possible solutions are proposed that incorporate advanced imaging and 3-D reconstruction technologies. InvertNet couples efficient digitization workflows with a highly robust network infrastructure capable of managing massive amounts of image data and related metadata and delivering high-quality images, including interactive 3-D reconstructions in real time via the Internet

Virtual Hardware for Operating Systems Development

Developing an operating system on bare hardware is difficult due to an inhospitable development environment, long edit-compile-run-debug times, and the need for extra target hardware. This paper contributes general techniques for creating virtual hardware for operating systems development. The virtual machine is realized on top of UNIX and is a close approximation of real hardware, including interrupts, time slicing, virtual memory, devices, multiple processors with separately programmable memory management units, and the ability to run application programs natively. Debugging and testing our operating system in such an environment was considerably quicker and easier compared to developing on bare hardware. 1 Introduction Developing operating systems is difficult on bare hardware. There is a paucity of tools for run time and post mortem debugging, as well as execution profiling. Rapid prototyping requires quick edit-compilerun -debug cycles. Fast turnarounds are a problem when machin..

Improving multi-tier security using redundant authentication

Multi-tier web server systems are used in many important contexts and their security is a major cause of concern. Such systems can exploit strategies like least privilege to make lower tiers more secure in the presence of compromised higher tiers. In this paper, we investigate an extension of this technique in which higher tiers are required to provide evidence of the authentication of principals when they make requests of lower tiers. This concept, which we call redundant authentication, enables lower tiers to provide security guarantees that improve significantly over current least privilege strategies. We validate this technique by applying it to a practical Building Automation System (BAS) application, where we explore the use of redundant authentication in conjunction with an authentication proxy to enable interoperation with existing enterprise authentication services

Adaptation and Synchronization in Bandwidth-Constrained Internet Video and Audio

Systems for the real-time transmission of video and audio on low-bandwidth lines must account for the limited bandwidth available, the bandwidth variance, packet loss rates, as well as CPU load. Vosaic, short for Video Mosaic, integrates real-time continuous media within standard Web pages, and handles the issues of transmitting continuous media with the Video Datagram Protocol (VDP). VDP dynamically adapts the media stream to the available network and CPU bandwidth, thus improving video performance. Built as an object-oriented framework, Vosaic permits the easy addition and customization of the basic VDP protocol for different media types. This family of protocols currently support two different standard video formats, as well as four audio formats. 1 Introduction Early systems for the delivery of real-time video and audio on the Internet, such as Berkeley's CM Player[12], required high-end workstations and high-speed Ethernet or T1 data rates. These systems concentrated on transmitt..