Conventional methods supporting Java binary security mainly rely on the security of the host Java Virtual Machine (JVM). However, malicious Java binaries keep exploiting the vulnerabilities of JVMs, escaping their sandbox restrictions and allowing attacks on end-user systems. Administrators must confront the difficulties and dilemmas brought on by security upgrades. On the other hand, binary rewriting techniques have been advanced to allow users to enforce security policies directly on the mobile code. They have the advantages of supporting a richer set of security policies and a self-constrained written code. However, the high administrative and performance overhead caused by security configuration and code rewriting have prevented rewriters from becoming a practical security tool. In this paper, we address these problems by integrating binary code rewriters with Web caching proxies and build the security system called PB-JARS, a Proxy-based JAva Rewriting System. PB-JARS works as a complimentary system to existing JVM security mechanisms by placing another line of defense between users and their end-user systems. It gives system administrators centralized security control and management for the mobile code and security policies. We evaluated PB-JARS using a real Java binary traffic model derived from analyzing real Web trace records. Our results show that adding binary rewriting to a Web caching system can be very efficient in improving end-host security at a low cost.

Binary rewriting techniques have been developed to allow users to enforce security policies directly on mobile code. However, the performance overheads incurred for improved security, particularly in large organizations with many end-hosts, accentuate the inherent challenges of code rewriting and limit the rate of improvement in these systems. We integrate a binary code rewriter with a web caching proxy and build the security system called PBJARS, a Proxy-based JAva Rewriting System. PBJARS compliments existing JVM security mechanisms by placing another line of security defense in the code path code associated with code downloads. It gives system administrators centralized security control at the level of administrative domains at proxy servers. We evaluated PB-JARS using real Java binary traffic models derived from analyzing real web trace records. Our experimental results show that the overhead added by binary rewriting can be significantly amortized by web caching and PB-JARS adds negligible performance impact on proxy servers.

The Oasis+ distributed storage system is a reliable memory store for small scale computing clusters. It is implemented entirely in-memory using Distributed Shared Memory (DSM) and was built to operate as a backbone service for a computing cluster that supports mobile workstations or remote clients needing fast access to storage. The system can store data quickly in a dependable manner in part by using a highperformance, high-availability page-based protocol called BR [1]. BR guarantees robust functionality despite multiple site failures that could occur. By integrating address range locking and eager release consistency (ERC) [2] Oasis+ provides a flexible and efficient platform for the development of distributed services. Reliability is achieved by replication and corrective cleanup recovery actions once failures arise.

We consider scheduling soft real-time tasks for a cluster which consists of multiple servers. Each server provides identical services where an incoming task can be assigned to one of the servers. The question we investigate is which assignment produces the best performance given two alternative approaches to queue the arriving tasks: a centralized approach or a distributed one. A missed deadline criterion is used to evaluate these approaches. The influence of dispatching policies on the performance of the distributed approach is also considered.

This paper evaluates the Dynamic Boundary Restricted protocol with phase-checking (DBRpc). DBRpc is a highly-adaptable extension of DBR that can respond to changes in the network environment and application workload. DBRpc is suitable for reliable shared memory systems that require rapid and complete response to site failures and phase changes. In this paper, we compare DBRpc with traditional protocols as well as variants of the BR/DBR class of protocols. We find that DBRpc offers unequaled adaptability and availability while having competitive operation costs.

IBM's Microkernel, named Workplace OS microkernel,1 was the core component of Workplace OS, a portable successor of OS/2. The basic premise of Workplace OS work was (1) IBM would adopt and improve the CMU Mach 3.0 microkernel for use on PDAs, the desktop, workstations, and massively parallel machines, and (2) that several operating system personalities would execute on the microkernel platform concurrently. This architecture would allow users to switch between applications written for different operating systems while IBM would also benefit by having one common platform for all product lines. The goals of the microkernel and the technical features of design are described in this paper. We also present lessons that may benefit future projects with similar goals. © 1998 John Wiley & Sons, Ltd.

Larger size networks require Distributed Shared Memory (DSM) coherence protocols which scale well. Fault-tolerance in terms of high availability is required for data access and for uninterrupted DSM service since large-scale environments have a greater number of potentially malfunctioning components. We present a new class of coherence protocols for DSM systems whose instances offer highly available access to shared data at low operation costs. The protocols proposed scale well; an increase in the number of client sites does not increase the operation costs after a certain threshold has been reached. The results presented in this paper give strong guidelines for the overall design of DSM systems which offer highly available, uninterrupted services.

DSM coherence protocols should scale well for large networks. Fault-tolerance in terms of highly available data access and uninterrupted DSM service is needed in large-scale environments that have a greater number of potentially malfunctioning components. We present a new class of dynamic coherence protocols for DSM systems in error-prone networks whose instances offer highly available access to DSM data at low operation costs. The approach is based on the highly scalable Boundary-Restricted (BR) coherence protocol class. The new protocol class, called the Dynamic Boundary-Restricted (DBR) coherence protocol class, maintains read/write frequencies of DSM requests at run-time. This information is used to dynamically adjust the minimum number of cached copies of a single DSM page in order to guarantee a given degree of data availability. The description of the new protocol class is accompanied by an analysis covering a large variety of workloads. This analysis presents the overall savings achieved by using a DBR coherence protocol in comparison to a static BR protocol.

Fault-tolerant distributed shared memory systems do not always need to support a complete and consistent recovery after a failure. We describe a framework, within which different approaches to, and different degrees of consistency and recoverability can be understood. The addition of consistent failure recovery may be approached from two different viewpoints: either by an application-oriented view or a memory-oriented view. The major characteristics used in our framework are variations of availability, consistency, and application support. The paper explains the basic model, which is used in RELIABLE MIRAGE+, and describes how the framework can be used by other researchers to understand and classify solutions to the reliable DSM problem. The model distinguishes a recoverable system, which must be able to survive any single-site failure, from a reliable system which also ensures consistency after the recovery. Since consistency requirements may impose a high penalty on standard operational performance, various relaxed recoverability consistencies are described by the multi-level model. Recovery under this model may be accomplished by applications specifying consistency and availability requirements.

False sharing reduces system performance in shared memory systems. A major impediment to solving the problem of false sharing has been that no satisfactory definition for this problem exists. In this paper we provide precise and intuitive definitions for several types of degenerate sharing, including false sharing.

Abstract We describe the evolution of a distributed shared memory (DSM) system, Mirage, and the difficulties encountered when moving the system from a Unix‐based* kernel on the VAX to a Unix‐based kernel on personal computers. Mirage provides a network transparent form of shared memory for a loosely coupled environment. The system hides network boundaries for processes that are accessing shared memory and is upward compatible with the Unix System V Interface Definition. This paper addresses the architectural dependencies in the design of the system and evaluates performance of the implementation. The new version, MIRAGE+, performs well compared to Mirage even though eight times the amount of data is sent on each page fault because of the larger page size used in the implementation. We show that performance of systems with a large page size to network packet size can be dramatically improved on conventional hardware by applying three well‐known techniques: packet blasting, compression, and running at interrupt level. The measured time for a page fault in MIRAGE+ has been reduced 37 per cent by sending a page using packet blasting instead of using a handshake for each portion of the page. When compression was added to MIRAGE+, the time to fault a page across the network was further improved by 47 per cent when the page was compressed into one network packet. Our measured performance compares favorably with the amount of time it takes to fault a page from disk. Lastly, running at interrupt level may improve performance 16 per cent when faulting pages without compression.

Shared memory is an effective and efficient paradigm for interprocess communication. We are concerned with software that makes use of shared memory in a single site system and its extension to a multimachine environment. Here we describe the design of a distributed shared memory (DSM) system called Mirage developed at UCLA. Mirage provides a form of network transparency to make network boundaries invisible for shared memory and is upward compatible with an existing interface to shared memory. We present the rationale behind our design decisions and important details of the implementation. Mirage's basic performance is examined by component timings, a worst case application, and a “representative” application. In some instances of page contention, the tuning parameter in our design improves application throughput. In other cases, thrashing is reduced and overall system performance improved using our tuning parameter.

This paper describes new interprocess communications facilities that have been added to the Locus system [POPEK 81][WALKER 83]. The facilities improve Locus's interprocess communication repertoire by providing distributed support for three separate subsystems from System V UNIX: messages, semaphores, and shared memory. Here we describe these subsystems and their integration into in the Locus architecture.