This paper evaluates the design and implementation of Omniware: a safe, efficient, and language-independent system for executing mobile program modules. Previous approaches to implementing mobile code rely on either language semantics or abstract machine interpretation to enforce safety. In the former case, the mobile code system sacrifices universality to gain safety by dictating a particular source language or type system. In the latter case, the mobile code system sacrifices performance to gain safety through abstract machine interpretation.Omniware uses software fault isolation, a technology developed to provide safe extension code for databases and operating systems, to achieve a unique combination of language-independence and excellent performance. Software fault isolation uses only the semantics of the underlying processor to determine whether a mobile code module can corrupt its execution environment. This separation of programming language implementation from program module safety enables our mobile code system to use a radically simplified virtual machine as its basis for portability. We measured the performance of Omniware using a suite of four SPEC92 programs on the Pentium, PowerPC, Mips, and Sparc processor architectures. Including the overhead for enforcing safety on all four processors, OmniVM executed the benchmark programs within 21% as fast as the optimized, unsafe code produced by the vendor-supplied compiler.

A data breakpoint associates debugging actions with programmer-specified conditions on the memory state of an executing program. Data breakpoints provide a means for discovering program bugs that are tedious or impossible to isolate using control breakpoints alone. In practice, programmers rarely use data breakpoints, because they are either unimplemented or prohibitively slow in available debugging software. In this paper, we present the design and implementation of a practical data breakpoint facility.

One way to provide fault isolation among cooperating software modules is to place each in its own address space. However, for tightly-coupled modules, this solution incurs prohibitive context switch overhead. In this paper, we present a software approach to implementing fault isolation within a single address space.Our approach has two parts. First, we load the code and data for a distrusted module into its own fault do main, a logically separate portion of the application's address space. Second, we modify the object code of a distrusted module to prevent it from writing or jumping to an address outside its fault domain. Both these software operations are portable and programming language independent.Our approach poses a tradeoff relative to hardware fault isolation: substantially faster communication between fault domains, at a cost of slightly increased execution time for distrusted modules. We demonstrate that for frequently communicating modules, implementing fault isolation in software rather than hardware can substantially improve end-to-end application performance.

article Free Access Share on Efficient data breakpoints Author: Robert Wahbe View Profile Authors Info & Claims ACM SIGPLAN NoticesVolume 27Issue 9Sept. 1992 pp 200–212https://doi.org/10.1145/143371.143518Online:01 September 1992Publication History 43citation514DownloadsMetricsTotal Citations43Total Downloads514Last 12 Months10Last 6 weeks3 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

The DASH resource model is defined as a basis for reserving and scheduling resources (disk, CPU, network, etc.) involved in end-to-end handling of continuous-media (information flowing continuously over real time i.e. digital audio or digital video) data. The model uses primitives that express work-load characteristics and performance requirements, and defines an algorithm for negotiated reservation of distributed resources. This algorithm is embodied in the session reservation protocol, a backward-compatible extension of the Internet Protocol. Hardware trends and future applications that motivate the DASH resource model are described. The performance requirements for using continuous media and the limitations of existing systems are discussed. The DASH resource model for reserving and scheduling resources is presented. The DASH kernel is briefly described.>