B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczynski, D. Becker, C. Chambers, and S. Eggers. Extensibility safety and performance in the spin operating system. In SOSP '95: Proceedings of the fifteenth ACM symposium on Operating systems principles, pages 267--283, New York, NY, USA, 1995. ACM Press.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....but signi cantly more precise tools need to be developed. Di erent types of applications may require di erent policies in order to achieve optimal performance and power eciency. Supporting all policies within a single monolithic kernel may not be possible. The use of micro kernels [34] like Spin [5], and the Aegis Exokernel [16] instead of monolithic kernels provides the opportunity to ne tune policies according to the requirements of each application. For example, two library operating systems, one optimized for performance and the other for reduced power consumption could be provided ....

Bershad, B. N., Savage, S., Pardyak, P., Sirer, E. G., Fiuczynski, M. E., Becker, D., Chambers, C., and Eggers, S. Extensibility safety and performance in the SPIN operating system. In Proc. of the 15th Symposium on Operating Systems Principles (Dec. 1995), pp. 267-283.

....for making an operat ing system self monitoring. The details are presented in the context of the VINO operating system, on which a prototype self adapting system is being built. However, the principles and approaches are applicable to any number of systems that support extensibility (e.g. SPIN [2]) VINO is an extensible operating system designed to provide resource intensive applications greater control over resource management. VINO supports the downloading of kernel extensions (grafts) which are written in C and protected using software fault isolation. To facilitate graceful ....

Bershad, B., Savage, S., Pardyak, P., Sirer, E.G., Fiuczynski, M., Becker, D., Eggers, S., Chambers, C., "Extensibility, Safety, and Performance in the SPIN Operating System," Proceedings of the 15th Symposium on Operating System Principles, Copper Mountain, CO, Dec. 1995, 267-284.

....NetBSD [44] At present, paths have been used in Scout largely for MPEG video decoding and display and not for protocol processing or other I O operations. In contrast, we have successfully used RIO for a number of real time avionics applications [19] with deterministic QoS requirements. SPIN [79, 80] provides an extensible infrastructure and a core set of extensible services that allow applications to safely change the OS interface and implementation. Application specific protocols are written in a typesafe language, Plexus, and configured dynamically into the SPIN OS kernel. Because these ....

B. Bershad, "Extensibility, Safety, and Performance in the Spin Operating System," in Proceedings of the 15 ACM SOSP, pp. 267--284, 1995.

....provide quality of service and other real time guarantees. Scout s notion of a path aligns control flow and data transfer and enables optimizations that benefit both overhead components at the same time, while also introducing new optimization opportunities. Extensible operating systems like Spin [12] or Exokernel [36] allow applications to implement specialized operating system functionality in an extensible kernel, which results in better performance for many applications for which the general purpose interface of monolithic kernels is inappropriate. Consequently, the interface provided by ....

B.N. Bershad et al., "Extensibility, Safety and Performance in the SPIN Operating System," Proc. 15th ACM Symp. Operating System Principles (SOSP-15), ACM Press, New York, N.Y., 1995, pp. 267-284.

....section, we describe the performance requirements that an RTOS must satisfy to be feasible for embedded applications. Section 3 presents a brief overview of EMERALDS. Section 4 shows how EMERALDS, as a real time embedded OS, is different from more generalized microkernels like Mach [14] and SPIN [15]. Sections 5 8 give details of our scheduling, synchronization, message passing, and system call schemes, respectively. Performance of these schemes is evaluated in Section 9 and we conclude with Section 10. 2 Embedded Application Requirements Our target embedded applications use single chip ....

....Different Microkernel optimization has been an active area of research in recent years, but little effort has been made in addressing the needs of real time systems, let al..one small memory embedded ones. In microkernels designed for general purpose computing such as Mach [14] L3 [25] and SPIN [15], researchers have focused on optimizing kernel services such as thread management [26, 27] IPC [28] and virtual memory management [29] Virtual memory is not a concern in our target applications. Thread management and IPC are important but not for the same reasons as for general purpose ....

B. Bershad, S. Savage, P. Pardyak, E. Sirer, M. Fiuczynski, D. Becker, C. Chambers, and S. Eggers, "Extensibility, safety and performance in the SPIN operating system," in Proc. Symp. Operating Systems Principles, pp. 267--284, 1995.

....media (audio and video) and batch traffic (FTP, NFS, etc. in the face of lost and misordered data [Clark90] Three projects which are based around this notion are the University of Cambridge s Nemesis project [Leslie96] MIT s Exokernel [Engler95] and the University of Washington s SPIN project [Bershad95]. Nemesis and Exokernel both adhere to the vertical operating system model whereby the OS provides only the minimal functionality necessary to share devices. However, they differ in their perceptions of what this minimal level of functionality is whilst Nemesis implements what are put forward ....

Brian Bershad et al.; "Extensibility, Safety and Performance in the SPIN Operating System", Proceedings of the 15th ACM Symposium on Operating Systems Principles (December 1995), pp.267--284.

....However, these techniques are focused to specific kernel interfaces, and its use is typically restricted to privileged users. There is a considerable amount of research on building extensible systems, a kind of systems that would allow generic, safe, and application specific extensions (e.g. SPIN[5], VINO[16] although this research is biased towards safety concerns of in kernel extensions. In contrast to the above techniques, we are taking a generic approach. Our goal is to enable extensions to be attached at any available interface, by providing convenient binding mechanisms for these ....

B. Bershad et al. "Extensibility, Safety and Performance in the SPIN Operating System", In Proc. of the 15th SOSP, 1995

....to a specific need. This is achieved through the definition of a Meta Object Protocol (MOP) i.e. a management interface, as a fundamental characteristic of every extensible service. Unless otherwise stated, the following projects employ an ad hoc approach to service design. 3.3.3. 1 SPIN SPIN [Bershad,95c] from the University of Washington had its original white paper produced in 1994 (reworked in [Bershad,95a] thus making it one of the most mature examples of this type of system. In SPIN, application defined system services are decomposed into three sub units; SPIN Dynamically Linked ....

Bershad, B.N., Savage, S., Przemyslaw, P., Sirer, E.G., Fiuczynski, M.E., Becker, D., Chambers, C., Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System". Proceedings of the 15th ACM Symposium on Operating Systems Principles, pp 267-284, Copper Mountain CO, U.S.A., December 1995.

....Conventional approaches The conventional approaches are classified into three categories, roughly speaking. One is the approach of the monolithic kernel such as UNIX [17] Another is the approach of the microkernel such as Mach [1] The other is the approach of the extensible kernel such as SPIN [3, 4]. In this section, we describe the feature of these conventional approaches, and then their disadvantages. 5 2.2.1 Monolithic kernel In the monolithic kernel, all facilities that the operation system should possess are in the kernel. Of course, all file systems are also embedded into the ....

Bershad, B., S. Savage, P. Pardyak, E. G. Sirer, D. Becker, M. Fiuczynski, C. Chambers, and S. Eggers, "Extensibility, Safety and Performance in the SPIN Operating System," in Proceedings of the 15th ACM Symposium on Operating System Principles (SOSP-15), pp. 267--284, Copper Mountain, CO., Dec. 1995.

....packet filters have been proposed. The BSD packet filter [24] redesigns the original stack based packet filter and is up to 20 times faster. The dynamic packet filter (DPF) 10] uses dynamic code generation and is 10 to 50 faster than the other fastest packet filters. The SPIN operating system [4] allows the users to download the extension modules written in Modula 3 [27] into the kernel. Modula 3 is a type safe language and does not cause memory access violation at runtime. Although Modula 3 is a general language and enables programmers to write most functions of operating systems, the ....

Bershad, B. N., S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczynski, D. Becker, S. Chambers, and C. Eggers, "Extensibility, Safety and Performance in the SPIN Operating System," in Proceedings of the 15th ACM Symposium on Operating Systems Principles, pp. 267--284, Dec. 1995.

....best effort applications and off line initialization. Work subsequent to Govindan has made use of trusted kernel modules rather than opening up a hole into the kernel address space for all applications. The efficacy of this approach has been investigated in detail in the SPIN operating system [Be95] and this is widely accepted as a safe compromise for services that need improved efficiency and resource control, yet maintaining overall system safety for applications. Based on this related research history on in kernel pipeline frameworks, the RT EPA employs the trusted module mechanism and ....

....user code and one for operating systems code. However, the RT EPA facility allows trusted module code to be executed in the kernel protection domain. We have focused on the functionality of architecture, relying on the existence of other technology such as that used in the SPIN operating system [Be95] to provide compile time safety checking. The negotiation control provided by RT EPA is envisioned to support isochronal event driven applications which can employ and control these pipelines for guaranteed or reliable execution performance. 5.2 RT EPA Traditional Hard Real Time Features The ....

Bershad, B., Fiuczynski, M., Savage, S., Becker, D., et al., "Extensibility, Safety and Performance in the SPIN Operating System", Association for Computing Machinery, SIGOPS '95, Colorado, December 1995.

....IPC facility to preserve an API with copy semantics and offer bi directional copy avoidance. Extensible kernel systems can, in principle, make it safe for users to install, modify, or customize kernel level servers. The usual price of safety, however, is run time overheads: For example, SPIN [1] requires extensions to be written in a type safe language, and VINO [18] encapsulates extensions for software fault isolation. These safety techniques have been reported to make code run from 10 to 150 more slowly [19] Additionally, kernel level debuggers of extensible kernel systems have been ....

B. Bershad, S. Savage, P. Pardyak, E. Sirer, M. Fiuczynski, D. Becker, C. Chambers and S. Eggers, "Extensibility, Safety and Performance in the SPIN Operating System", Proc. 15th SOSP, ACM, Dec. 1995, pp. 267-284.

....new binding factories from existing components. Prominent among the components are a range of filter objects for common media formats. 8. RELATED WORK There is currently considerable ongoing research in the area of extensible and adaptable operating systems. Key examples include Spin [1], Exokernel Aegis [8] and Spring [19] The aim of this work is to introduce flexibility in operating system structures to allow, for example, the addition of new services. In general, however, this research has not considered the requirements of mobile multimedia applications. In addition, we ....

Bershad, B.N., S. Savage, P.Przemyslaw, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chambers, S. Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System". Proc. 15 th ACM SOSP, pp267-284, Copper Mountain CO, USA, December 1995.

....introduce the recursive virtual machines that allow the code to execute in a separate trusted domain. SPIN system addresses security by enabling the secure execution of the code within the kernel. In particular it addresses the kernel extensibility by safely executing extensions within the kernel. [11]. Operating systems were instrumented to provide information on various physical and logical resources, such as in COCANET [63] and in the work by Huang et al. 35] This was done for the purpose of load distribution and performance evaluation. In the Stealth scheduler [45] VM was prioritized ....

B. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. Fiuczinski, D. Becker, C. Chambers, and S. Eggers, "Extensibility, Safety and Performance in the SPIN Operating System," Proceedings of the 15th Symposium on Operating Systems Principles, pp 267--284.

....used objects into a small number of pages [Seidl97] Some database servers allow clients to load query or data type specific code into the server to improve performance. The Thor database server uses a typesafe language, Theta, for writing these extensions [Liskov95] The SPIN operating system [Bershad95] is written in Modula 3 and uses it as its extension language as well. A disadvantage of requiring that extensions be written in a safe language is that the extensible system either needs to be written entirely in the language used for writing extensions, or the system needs to deal with the ....

....or user activity. We may not wish to give the extension all events as they arrive (for privacy or performance reasons) and so we need to filter the event stream, passing on only the events that meet the appropriate criteria. This is the event model used by the SPIN extensible operating system [Bershad95]; more on SPIN is found below. Filtering for privacy ensures that an extension that has permission to, say, listen on one TCP socket is not able to view all incoming TCP packets. Filtering for performance would be done if an extension wants to see only a subset of some type of event, and we do ....

[Article contains additional citation context not shown here]

Bershad, B., Savage, S., Pardyak, P., Sirer, E. G., Fiuczynski, M., Becker, D., Eggers, S., Chambers, C., "Extensibility, Safety, and Performance in the SPIN Operating System," Proceedings of the 15th Symposium on Operating Systems Principles, Copper Mountain, CO (December 1995).

....on the future of a computation. Furthermore, we use graphs in a novel way and allow them to be associated with events. This enables us to encapsulate functionality using graphs and dynamically bind such functionality to objects. Our model shares many characteristics with projects such as SPIN [5], Coyote [6] and Ensemble [16] that use an event architecture as the basis for flexibility, extensibility, and component interaction. One may view Legion as a configurable operating system 27 specifically designed for metacomputing. However, Legion does not replace the operating system on host ....

B. Bershad et al., "Extensibility, Safety and Performance in the SPIN Operating System", Proceedings of the Fifteenth ACM Symposium on Operating System Principles, pp. 267-284, Copper Mountain, CO, 1995.

....and the Autopilot toolkit provides closed loop, automatic control mechanisms besides interactive steering. The diversity in hardware and software configurations, and the resulting performance variations gave rise to several operating systems research projects. Exokernel [62] Choices [63] SPIN [64], and 2K [65, 66] are experimental operating systems that provide mechanisms for dynamically configuring the operating components to match the execution environment. This adaptivity is achieved through dynamic component attachments or new code downloads. We believe our adaptive file system ....

B. Bershad, S. Savage, P. Pardyak, E. Sirer, M. Fiuczynski, D. Becker, C. Chambers, and S. Eggers, "Extensibility, Safety and Performance in the SPIN Operating System," ACM Operating Systems Review, vol. 29, no. 5, pp. 267--284, 1995.

....switching fabrics using message passing and one common addressing scheme for all communication. What remains is to provide an efficient execution environment for message handling. 3.2. Events and messages I 2 O applications are modeled following an event based processing and communication scheme [23]. Such an approach gives us the necessary flexibility that we need in ever changing environments. In this context an event is the reception of a message. It triggers the execution of user supplied application software that has been associated with the message at configuration time. Through this ....

B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczunski, D. Becker, C. Chambers, S. Eggers. "Extensibility, Safety and Performance in the SPIN Operating System", in Proceedings of the Fifteenth ACM Symposium on Operating System Principles, pp. 267-284, December 3-6, 1995, Copper Mountain Resort, Colorado, USA.

....1.1 Motivation On the research in finding a way for efficient system software components, a fact is found to answer the questions. It is found that traditional systems can t meet al..l the demanding needs for all applications because they are originally designed for servicing all the applications [Bershad 95] System performance usually degrades because of inducing this generality. If the system service can be specialized to meet application s needs, system performance will behave better and beyond what it is 3 that we cannot image before [Lee 94, Lee 96a, Lee 96b] Table 1 and Figure 1 illustrate ....

....of context switches between user and kernel space by abstracting underlying hardware and 7 providing them as libraries. In SPIN, applications could dynamically link their specialized codes into kernel to add new services, replace old ones or simply move the codes from user space to kernel space [Bershad 95] Real time and multimedia applications are getting more attentions in recent years. Real time applications generally have the property that requested data is meaningful only if data is arrived on time. Rajkumar et al. proposed a resource centric approach for designing operating system kernels ....

B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczynsky, D. Becker, C. Chambers and S. Eggers, `Extensibility, Safety and Performance in the SPIN Operating System', Proceedings of the 15 th ACM Symposium on Operating Systems Principles, Copper Mountain, CO, December 1995, pp. 267-284.

....user code and one for operating systems code. However, the RT PCIP facility allows untrusted code to be executed in the kernel protection domain. We have focused on the functionality of architecture, relying on the existence of other technology such as that used in the SPIN operating system [Be95] to provide compile time safety checking. The negotiative control provided by RT PCIP is envisioned to support isochronous and event driven applications which can employ and control these pipelines for guaranteed or reliable execution performance. 2.0 EPA DM Approach to Thread Scheduling The ....

Bershad, B., Fiuczynski, M., Savage, S., Becker, D., et al., "Extensibility, Safety and Performance in the SPIN Operating System", Association for Computing Machinery, SIGOPS '95, Colorado, December 1995.

....concerning where their tasks should execute [21] The ability to get specific finegrained amounts of resources, under process control, is lacking in most popular operating systems. However, new research systems are beginning to address this problem, including Exokernel [47] L5 [91] SPIN [22], Cache Kernel [31] Fluke[54] and Scout[102] Our approach differs either in the level of abstraction provided, or the granularity of resource control, or both. G.2.3.3 Network Communication Support Agents need to communicate with the client they left behind, with servers they visit, and, of ....

B. Bershad, S. Savage, P. Pardyak, E. Sirer, M. Fiuczynski, D. Becker, C. Chambers, and S. Eggers, "Extensibility, Safety and Performance in the SPIN operating system," Proc. 15th ACM Symp. on Operating System Principles (SOSP), December 1995, 267--284.

....(including, for example, the approach to inheritance) In the middle, there are systems which enable replacement or modification of some parts of the implementation. For example, the operating system Spin enables the user to insert selected modules (called Spindles) dynamically into the kernel [Bershad95]. It is therefore necessary to define reflection carefully with respect to this spectrum of options. The starting point for our definition of reflection is the concept of causal connection. According to Maes [Maes87] a system is said to be causally connected to its domain if the internal ....

....future operating system designs [Tunes98] A number of other researchers are interested in the general area of adaptive or extensible operating systems. While not using full reflection, these projects have contributed a number of interesting ideas. Examples of adaptive operating systems are Spin [Bershad95], Synthetix [Cowan96] Exokernel Aegis [Engler95] Spring [Mitchell94] Cache Kernel [Cheriton94] Choices [Campbell95] Kea [Veitch96] KTK [Gheith94] Scout [Montz94] and the more architectural work of Chris Maeda on service decomposition [Maeda93, Maeda94] There has also been some related work ....

Bershad, B.N., S. Savage, P.Przemyslaw, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chambers, S. Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System". Proceedings of the 15th ACM Symposium on Operating Systems Principles, pp 267-284, Copper Mountain CO, U.S.A., December 1995.

....Customisable Kernels A competing approach to the library operating system paradigm is the idea of providing a minimal kernel that may be dynamically specialised to safely meet the performance and functionality requirements of applications. Examples of systems which typify this approach are SPIN [6, 7] and Aegis [23] The motivation for these customisable or extensible kernels is the same as for library operating systems. In fact, the two approaches overlap to some extent as illustrated by Aegis. The SPIN system consists of a set of core system services such as memory management and ....

B.N. Bershad, S. Savage, P. Pardyak, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chambers, and S. Eggers. "Extensibility, Safety, and Performance in the SPIN Operating System", in Proceedings of the Fifteenth ACM Symposium on Operating System Principles, Copper Mountain, Colorado, 1995.

....provided. Customisable Kernels A competing approach to the micro kernel operating system paradigm is the idea of providing a minimal kernel that may be dynamically specialised to safely meet the performance and functionality requirements of applications. The best example of this approach is SPIN [9]. The SPIN system consists of a set of core system services such as memory management and scheduling, and a set of extension services that enable developers to customise the behaviour of the operating system. Customisation is achieved by loading extensions into the kernel where they are integrated ....

B.N. Bershad, S. Savage, P. Pardyak, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chambers, and S. Eggers . "Extensibility, Safety and Performance in the SPIN Operating System" , in Proceedings of Proceedings of the Fifteenth Symposium on Operating Systems Principles (SOSP 15), December 1995.

....of general purpose operating systems, certain extension mechanisms provide a tradeoff between the level of safety provided and the performance achieved. Isolated address spaces and in kernel modules form the two extremes of this spectrum. An ideal mechanism, that of language based protection [4], affords good performance as well as safety if the compiler can be trusted, and the router implementation as well as the extensions are written in a type safe, modular language. Since safety of the router s core functionality is a key concern, the only applicable extension mechanisms are those ....

....specifies guidelines for extensible router OS design, the issues of scheduling, interrupt suppression and co location are not discussed, though it seems that the protection model is a combination of isolated address spaces with Java [7] based extensions. Extensible operating system literature [4, 21] proposes various means like binary rewriting and safe languages to implement extensions. Of course, the exact interface for extensibility is dependent upon the system requirements. While [4, 21] discuss such interfaces for extending general purpose operating systems, our focus is on defining an ....

[Article contains additional citation context not shown here]

Bershad, B.N.; Savage, S.; Pardyak, P.; Sirer, E.G.; Fiuczynski, M.E.; Becker, D.; Chambers, C.; Eggers, S., "Extensibility, safety and performance in the SPIN operating system ," ACM Operating Systems Review, vol.29, no.5, p. 267-84, Dec. 1995.

....and NetBSD [22] At present, paths have been used in Scout largely for MPEG video decoding and display and not for protocol processing or other I O operations. In contrast, we have successfully used RIO for a number of real time avionics applications [9] with deterministic QoS requirements. SPIN [43, 44] provides an extensible infrastructure and a core set of extensible services that allow applications to safely change the OS interface and implementation. Applicationspecific protocols are written in a typesafe language, Plexus, and configured dynamically into the SPIN OS kernel. Because these ....

B. Bershad, "Extensibility, Safety, and Performance in the Spin Operating System," in Proceedings of the 15 th ACM SOSP, pp. 267--284, 1995.

....code will be primary concerned with data processing (i.e. primarily low cycles byte computations) this overhead must be low enough to not negate the benefits of on drive execution. 2.5. 4 Fault Isolation Work in safe operating system extensions, software fault isolation, and proof carrying code [Bershad95, Small95, Wahbe93, Necula96] provides a variety of options for safely executing untrusted code. The SPIN work depends on a certifying compiler that produces only safe object code from the source code provided by the user. The downside is that this requires access to the original source code and depends heavily on ....

Bershad, B.N., Savage, S., Pardyak, P., Sirer, E.G., Fiuczynski, M.E., Becker, D., Chambers, C. and Eggers, S. "Extensibility, Safety, and Performance in the SPIN Operating System" SOSP, December 1995.

....OS abstractions to coexist or override the default set. Pebble can use the interposition technique discussed in Section 6 to wrap a sandbox around untrusted code. Several extensible operating system projects have studied the use of software techniques, such as safe languages (e.g. Spin [Bershad95]) and software fault isolation (e.g. VINO [Seltzer96] for this purpose. Where software techniques require faith in the safety of a compiler, interpreter, or software fault isolation tool, a sandbox implemented by portal interposition and hardware memory protection provides isolation at the ....

....W. Bolosky, D. Golub, R. Rashid, A. Tevanian, M. Young, Mach: A New Kernel Foundation for UNIX Development, Proc. Summer 1986 USENIX Conf. pp. 93 112 (1986) Bershad89] B. Bershad, T. Anderson, E. Lazowska, H. Levy, Lightweight Remote Procedure Call, Proc. 12th SOSP, pp. 102 113 (1989) [Bershad95] B. Bershad, S. Savage, P. Pardyak, E. Sirer, M. Fiuczynski, D. Becker, C. Chambers, S. Eggers, Extensibility, Safety, and Performance in the SPIN Operating System, Proc. 15th SOSP, pp. 267 284 (1995) portal spec. portal len (instr. time (cycles) cycles per instr. smcii 64 7282 114 ....

[Article contains additional citation context not shown here]

B. Bershad, S. Savage, P. Pardyak, E. Sirer, M. Fiuczynski, D. Becker, C. Chambers, S. Eggers, "Extensibility, Safety, and Performance in the SPIN Operating System,"

....Island, SC c fl1999 ACM 1 58113 140 2 99 0012. 5. 00 tensibility has prevailed in almost every major category of software systems, including extensible database systems [26] to which third party data blades can be added to perform type specific data processing, extensible operating systems [6, 15, 23], which support application specific resource management policies, programmable active network devices [1, 27] that allow protocol code running on network devices to be tailored to individual applications, and user level applications that dynamically integrate third party modules to augment the ....

....Appropriate inter component isolation makes it is easier to quarantine buggy components and pinpoint the cause of application malfunctioning. Although a number of approaches have been proposed to provide intra address space protection, such as software fault isolation [29] type safe languages [6], interpretive languages [17] and proof carrying code [19] none satisfies all the design goals of an ideal intra address space protection mechanism: safety from corrupting extension modules, low run time overhead, and programming simplicity. The commonality among all the above approaches is the ....

[Article contains additional citation context not shown here]

Bershad, B.N.; Savage, S.; Pardyak, P.; Sirer, E.G.; Fiuczynski, M.E.; Becker, D.; Chambers, C.; Eggers, S., "Extensibility, safety and performance in the SPIN operating system ," ACM Operating Systems Review, 29(5):267-84, Dec. 1995.

....manager through the object s public interface, and (3) strategies for controlling evolution are defined by the manager, and can be configured and restricted to meet the object type s needs. Recent research has focused on the dynamic extensibility and configurability of operating systems (e.g. Spin [6], Exokernel [12] network protocols (e.g. x kernel [17] and individual applications such as Web browsers. This paper reports on work that brings similar extensibility to distributed objects and metasystems. 2. Related work Current distributed computing systems do not support mechanisms that ....

Bershad, B., Savage, S., Pardyak, P., Sirer, E.G., Becker, D., Fiuczynski, M., Chambers, C., Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System," Proceedings of the 15th ACM Symposium on Operating System Principles (SOSP-15), pp. 267 - 284. October 1997.

....on the future of a computation. Furthermore, we use graphs in a novel way and allow them to be associated with events. This enables us to encapsulate functionality using graphs and dynamically bind such functionality to objects. Our model shares many characteristics with projects such as SPIN [5], Coyote [6] and Ensemble [17] that use an event architecture as the basis for flexibility, extensibility, and component interaction. One may view Legion as a configurable operating system specifically designed for metacomputing. However, Legion does not replace the operating system on host ....

B. Bershad et al., "Extensibility, Safety and Performance in the SPIN Operating System", Proceedings of the Fifteenth ACM Symposium on Operating System Principles, pp. 267-284, Copper Mountain, CO, 1995.

....control and data flow of objects and applications to obtain a desired fault tolerance policy, and hence could easily incorporate group communication primitives as part of our transformations. 2. 4 Reflection Reflection has been used successfully in several contexts, including operating systems [8], programming languages [16] 28] and in the construction of dependable systems [1] 16] 29] 39] Its use has also been advocated for the next generation of real time global databases [46] In [29] 39] the Common List Object System (CLOS) 28] is extended to support persistence using reflection. ....

B. Bershad et. al., "Extensibility, Safety and Performance in the SPIN Operating System", Proceedings of the 15 th ACM Symposium on Operating System Principles (SOSP-15), pp. 267-284, Copper Mountain, CO, 1995.

....of the agent) Different solutions have been proposed to try to protect the agent from possible attacks from the servers ( 9, 12, 1] Another security problem is how to protect the servers from malicious agents. Related work can be found based on different approaches like type safe languages ([3, 8]) and proofcarrying code ( 11] among others. Although the usefulness of agents to buy or sell products on their owners behalf is often pointed out, there exist few examples in the literature explicitly showing how this can be accomplished. In [10] the concept of intelligent trade agent (ITA) is ....

B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczynski, D. Becker, C. Chambers and S. Eggers, "Extensibility safety and performance in the spin operating system". In Proceedings of the Fifteenth Symposium on Operating System Principles, Dec. 1995.

....[13] 11] There are two main techniques used for implementing runtime extensible systems. ReAEective systems [14] 10] are object oriented and de ne a Meta Object Protocol (MOP) on system objects which can be used to modify aspects of the objects implementation or environment. Ad hoc systems [2], 12] 6] simply rely on exporting an API which empowers applications to extend parts of the system with their own code sequences at any instance in time. 3 Architectural Overview 3.1 Object Model DEIMOS adopts a mature and well understood object based model for the structuring of its system ....

Bershad, B.N., Savage, S., Przemyslaw, P., Sirer, E.G., Fiuczynski, M.E., Becker, D., Chambers, C., Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System". Proceedings of the 15th ACM Symposium on Operating Systems Principles, pp 267- 284, Copper Mountain CO, U.S.A., December 1995.

....examples of these needs, and describe the changes to Modula 3 that we have made for our work in the SPIN operating system. 1 Introduction SPIN is an extensible operating system that allows untrusted applications to extend system services by dynamically linking extension code into its kernel [2]. These extensions directly access system services with procedure calls, and system resources via loads and stores. As a result, extensions do not incur costly address space switches when they interact with the kernel. SPIN relies on language facilities to protect the system from extensions (and ....

B.N. Bershad, S. Savage, P. Pardyak, E.G. Sirer, M. Fiuczynski, D. Becker, S. Eggers, and C. Chambers. "Extensibility, Safety and Performance in the SPIN Operating System". In Proceedings of the 15th Symposium on Operating Systems Principles, pages 267--284, Copper Mountain, CO, December 3--6, 1995.

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B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczynski, D. Becker, C. Chambers, and S. Eggers. Extensibility safety and performance in the spin operating system. In SOSP '95: Proceedings of the fifteenth ACM symposium on Operating systems principles, pages 267--283, New York, NY, USA, 1995. ACM Press.

No context found.

Bershad, B.N., S. Savage, P.Przemyslaw, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chambers, S. Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System". Proc. 15 th ACM SOSP, pp267-284, Copper Mountain CO, USA, December 1995.

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B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. Fiuczynski, and B. E. Chambers, "Extensibil- ity, safety, and performance in the SPIN operating system," in Proceedings of the 15th ACM Symposium on Operating Systems Principles, pp. 267-- 284, 1995.

No context found.

B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. Fiuczynski, and B. E. Chambers, "Extensibility, safety, and performance in the SPIN operating system," in Proceedings of the 15th ACM Symposium on Operating Systems Principles, pp. 267-- 284, 1995.

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Brian Bershad, et al., "Extensibility, Safety and Performance in the SPIN Operating System," in Proceedings of the 15th ACM Symposium on Operating System Principles (SOSP-15). Copper Mountain, CO.

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B.N. Bershad, S. Savage, P. Pardyak, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chamers, and S. Eggers, "Extensibility, Safety, and Performance in the SPIN Operating System," Operating Systems Review, Vol. 29, No. 5, December 1995, pp. 267-84. Available at http://www.cs.washington.edu/research/projects/spin/www/papers/SOSP95/sosp95.ps

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B. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. Pitsczynski, D. lietket, S. Eggers, and C. Chambers, "Extensibility, safety and performance in the spin operating system," in Proc. 15th Symp. Operating Sytems Principles, Dec. 1995, pp. 267--284.

No context found.

B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. E. Fiuczynski, D. Becker, C. Chambers, and S. Eggers. Extensibility safety and performance in the SPIN operating system. In Proceedings of the 15 ACM Symposium on Operating Systems Principles, pages 267--283. ACM Press, 1995.

No context found.

B. Bershad, etc. "Extensibility, safety, and performance in the SPIN operating system", Proceedings of the 15th ACM Symposium on Operating System Principles, pages 267-284, Copper Mountain, CO, 1995.

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B. N. Bershad, S. Savage, P. Pardyak, E. G. Sirer, M. Fiuczynski, D. Becker, S. Eggers, and C. Chambers, "Extensibility, safety, and performance in the Spin operating system," Proc. of the 15th ACM Symposium on Operating System Principles, pp. 267-284, 1995.

No context found.

B.N. Bershad, S. Savage, P. Pardyak, E.G. Sirer, M.E. Fiuczynski, D. Becker, C. Chambers, S. Eggers, "Extensibility, Safety and Performance in the SPIN Operating System", Proceedings of SOSP'95.

No context found.

Bershad,B.N., et al., "Extensibility, Safety and Performance in the SPIN Operating System", Fifth ACM Symposium on Operating Systems Principles, Copper Mountain, December 1995.

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B.N. Bershad et al., "Extensibility, Safety and Performance in the SPIN Operating System," Proc. 15 th ACM Symp. Operating System Principles, No. 15, ACM Press, New York, 1995, pp. 267-284; available at http://www.acm.org/ pubs/articles/proceedings/ops/224056/p267bershad/p267bershad. pdf.

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BERSHAD,B.N.,SAVAGE, S., PARDYAK, P., SIRER,E.G.,FIUCZYNSKI,M.E.,BECKER, D., CHAMBERS, C., AND EGGERS, S. 1995. Extensibility safety and performance in the SPIN operating system. ACM SIGOPS Oper. Syst. Rev. 29, 5 (Dec.), 267--283.

No context found.

Bershad, B.N., Savage, S., Przemyslaw, P., Sirer, E.G., Fiuczynski, M.E., Becker, D., Chambers, C., Eggers, S., "Extensibility, Safety and Performance in the SPIN Operating System". Proceedings of the 15 th ACM Symposium on Operating Systems Principles, pp 267-284, Copper Mountain CO, U.S.A., December 1995.

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