A. Birrell, G. Nelson, S. Owicki, E. Wobber, Network objects, in: Symposium on Operating Systems Principles, ACM Press, 1993, pp. 217--230.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....models, such as those based on the 4 standard distributed system platforms (e.g. OMG CORBA, Sun Java, Microsoft . Net) those exhibited by recent mobile agents platforms (e.g. Voyager, Aglets, Grasshopper) or those exhibited in experimental platforms and languages such as Network Objects [4], Orca [17] Kali Scheme [11] Facile [16] Obliq [7] etc. These technologies improve on the traditional client server programming model, e.g. introducing ideas of shared objects, multi faceted components, migrating agents, or mobile code, but they fail to provide a uniform, formal model of ....

A.D. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network objects. In in Proceedings 14th Symp. on Operating Systems Principles (SOSP), 1993.

....is because JVML is a high level language with automatic memory management and garbage collection, and it provides no way to get around that. 2. 6 Consistent Java RMI Semantics Java supports remote method invocation (RMI) 43] which is a form of RPC and is based on the Modula 3 network objects [5]. But the Java RMI semantics for argument passing are inconsistent. While arguments to local methods calls are passed by reference, arguments to remote methods are sometimes passed by reference and sometimes by value. Ideally, all arguments to methods should be passed by reference to provide ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network objects. In Symposium on Operating Systems Principles (SOSP), December 1993.

....applications of type X ; I will be back at time Y ; If you get an agent from so and so, provide file Z as input . This presupposes an underlying mechanism for authentication and encryption. There is work in progress to provide secure communication and authentication at the Network Objects layer [5] the transport layer for Visual Obliq. In practice, there are likely to be other locale specific resources, such as file handles and network connections, that need to be preserved during migration. The replication of such resources cannot be automated since it is highly application and ....

....customized to the local environment. In addition, the rantime provides the following facilities: 3.3.1 Migration Support. It implements the migration commands described earlier. The rantime at the source accesses the agent server using a remote object access mechanism known as Network Objects [5]. Then it checkpoints the local interface. At the target site, the agent server copies the application state over and uses the local runtime to rebuild the interface. The two operations on the interface are implemented thus: a) Checkpointing the user interface. This is done by walking the Visual ....

Birrell, A.D., G. Nelson, S. Owicki, and E. Wobber, "Network objects". Proc. 14th Symposium on Operating Systems Principles. 1993.

....is because JVML is a high level language with automatic memory management and garbage collection, and it provides no way to get around that. 2. 6 Consistent Java RMI Semantics Java supports remote method invocation (RMI) 43] which is a form of RPC and is based on the Modula 3 network objects [5]. But the Java RMI semantics for argument passing are inconsistent. While arguments to local methods calls are passed by reference, arguments to remote methods are sometimes passed by reference and sometimes by value. Ideally, all arguments to methods should be passed by reference to provide ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network objects. In Symposium on Operating Systems Principles (SOSP), December 1993.

....is provided. Instead, the architecture allows consistency models to be applied on a per object basis. Furthermore, the consistency model applied to a given object may be changed dynamically. Most distributed systems services offer serializability as the basic (if not only) consistency model (e.g. [1], 2] Serializability is clearly very useful and could be implemented within this framework. However, observation of typical Internet 8 applications shows that serialization is often not used in these systems. Perhaps the most common model is simply to poll the server to detect changes to ....

....CORBA also has a set of optional CORBAservices, such as transactions and concurrency control[12] RMI provides only basic remote method invocation and remote object references. Note that both CORBA and RMI are quite similar to the Network Objects remote method invocation system[1]. The main feature that sets this project apart from CORBA and RMI is the ability to cache objects on the client machine. This has obvious performance advantages. More significant is the way CORBA and RMI tend to negatively influence design. Since method calls and network communication are so ....

A. Birrell, G. Nelson, S. Owicki, T. Wobber. Network Objects. In proceedings of the 14 th ACM Symposium on Operating Systems Principles, 1993.

....as NetEffect [6] RING [9] or Ultima Online [18] serialization of updates is implicitly performed, which removes the need for a special consistency protocol and simplifies distribution semantics. In fact, a master slave pair of an application instances has similar semantics like network objects [3], or even X windows [22] applications that separate user interface from application execution, only that Studierstube applications execute the user interface on both client and server. At the same time, the master host can be determined for every application instance separately. This implies that ....

Birrell, A., Nelson, G., Owicki, S., and Wobber, E. Network objects. In Proc. 14 th ACM Symp. on Operating Systems Principles, 1993.

....active. Such systems need to provide activation, a mechanism for providing persistent references to objects and managing the execution of object implementations. When warranted, object servers can be started up or shut down. As our platform for distributed objects, we use the network object system [1] provided with the Digital Equipment Corporation System Research Center distribution of the Modula 3 (M3) language [2] Given that this implementation platform does not support object activation, we have designed an activation protocol to address that need. We identify several important goals for ....

Birrell, Andrew, Greg Nelson, Susan Owicki, and Edward Wobber, "Network Objects," Digital Equipment Corporation Systems Research Center Technical Report 115 (1994).

....Spec) One way to obtain these would be to convert the PseudoIDL which specifies those operations using the mapping presented in Section 2. 4.0 Method implementations This document does not deal explicitly with method implementations. Methods can be implemented using DEC SRC s Network Objects [3, 4]; we have used SRC s implementation for the marshalling of parameters in method calls by replacing the definition of IDL.Object in Section 2.1 with NetObj.T. 5.0 Wish list The mapping presented here leaves out some things we would like to have. 5.1 Polymorphism of Object types While we achieve ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber, "Network Objects", Research report 115, Systems Research Center, Digital Equipment Corp., 1994.

....= RECORD string : IDL.String; bound : 16 END; 2.11 Mapping for Arrays IDL arrays of size x map to Modula 3 arrays indexed from 0 to x 1. Note that while array sizes in IDL are placed with declarators, array bounds in Modula 3 are placed with types. Example: struct position t2 float x[2] y[2][3]; maps to TYPE position t2 = RECORD x : ARRAY[0. 1] OF IDL.Float; y : ARRAY[0. 1] 0. 2] OF IDL.Float; END; 2.12 Mapping for Exceptions IDL exceptions map to Modula 3 exceptions. The built in exceptions all are subsumed using the predefined Modula 3 exception IDL.Exception. The mapped ....

....Spec) One way to obtain these would be to convert the PseudoIDL which specifies those operations using the mapping presented in Section 2. 4.0 Method implementations This document does not deal explicitly with method implementations. Methods can be implemented using DEC SRC s Network Objects [3, 4]; we have used SRC s implementation for the marshalling of parameters in method calls by replacing the definition of IDL.Object in Section 2.1 with NetObj.T. 5.0 Wish list The mapping presented here leaves out some things we would like to have. 5.1 Polymorphism of Object types While we achieve ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber, "Network Objects", Proc. 14th ACM Symp. On Operating Systems Principles, 1993.

....compiler [63] the benchmark, trestle, is a game that uses Trestle to do the windowing. Write pickle [81] is a simple tool which uses pickle, a facility for flattening and unflattening linked structures. Pickle forms a key component of many applications including a remote procedure call package [11] and the WPO. Table 4.1 Description of benchmark programs Name Lines Sites Description format [76] 395 37 Text formatter dformat [76] 602 95 Text formatter write pickle 654 19 Reads and writes an AST k tree [10] 726 13 Manages sequences using trees slisp 1,645 223 Small lisp interpreter pp ....

Birrell, A., Nelson, G., Owicki, S., and Wobber, E. Network objects. In Proceedings of the Fourteenth ACM Symposium on Operating Systems Principles, pages 217--230, 1993.

....Each mechanism can potentially cause difficulties. To ensure the right code, we compute the type identifiers that are stamped on each ANTS capsule from an MD5 [36] fingerprint of the corresponding code 2 . This is analogous to the way fingerprints are used to name the types of network objects [7]. We originally chose this method as a distributed naming scheme to eliminate the need for standardized protocol identifiers, but quickly came to value its security properties. It is secure because a belief that the fingerprint function is one way implies that the association between a capsule 1 ....

A. Birrell et al. Network objects. In 14th Symp. on Operating Systems Principles (SOSP'93), pages 217-- 230, Ashville, NC, Dec. 1993. ACM.

.... tools causes the application to become intractable ( complex things are not possible ) Of the tools available for integrating distributed objects into programming languages, client server data sharing is by far the most common approach, as exemplified by CORBA [26] Modula 3 Network Objects [5], and Java RMI [39] Unfortunately, interactive graphical applications, such as virtual reality, require that the data used to refresh the display be local to the process doing the rendering or acceptable frame refresh rates will not be achieved. Therefore, pure client server approaches are ....

....most important features for our work is that it gives us uniform access to these facilities across all architectures. Repo 3D relies on a number of Modula 3 libraries, as illustrated in Figure 2. Distributed data sharing is provided by two packages, the Network Object client server object package [5], and the Replicated Object shared object package [24] see Section 4.1) DistAnim 3D is derived from Anim 3D [25] a powerful, nondistributed, general purpose 3D library originally designed for 3D algorithm animation (see Section 4.2) Finally, Repo itself is a direct descendant of Obliq [8] and ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network Objects. In Proc. 14th ACM Symp. on Operating Systems Principles, 1993.

....standard buffering techniques to improve performance of certain distributed objects. The buffered collection and buffered iterator patterns allow efficient handling of collections of small primitive elements while supporting conventional distributed object semantics through remote proxy objects[3][4]. Specifically, the patterns apply to remote proxies for collections that are composed of very large numbers of small primitive elements in collection form. These patterns are motivated by the following forces: latency networks, RPCs, process context switching all add up to a great deal of ....

....the collection in situations that aren t strictly iterative. Lazy Evaluation of the buffered data some systems might benefit from collections which transmit and marshall unmarshall buffered data on demand rather than as it is added to the collection. 13.0 See Also Remote Proxy pattern [3] [4] Iterator pattern [3] 14.0 Acknowledgments The following individuals contributed to the development and refinement of this pattern: Douglas Schmidt schmidt cs.wustl.edu Rich Strobel rich strobel mentorg.com Robert Todd robert todd mentorg.com George. Moberly georgem homer.atria.com ....

A. Birrell, G. Nelson, S. Owicki, E. Wobber, "Network Objects," Digital Systems Research Center, Feb 1994

....and contrast these approaches. We conclude that while Java with RMI support offers significant advantages over its more traditional counterparts to programming heterogeneous networks, it lacks certain features that would enhance its expressivity. 2 Motivation Like many distributed languages [3, 5], Java s sequential core is object based. A Java class defines a datatype, and an object is an instance of that type. Operationally, an object defines a collection of data along with operations on that data. A distributed Java program can be now viewed as a collection of objects resident on ....

Birrell, A., Nelson, G., Owicki, S., and Wobber, E. Network Objects. In 14th ACM Symposium on Operating Systems Principles (1993 December).

....at the server site. Instance arrays, form constructors and other forms of global code are placed in the initial, common scope at the serversite, and are hence globally visible. The Obliq distribution and data sharing mechanisms are built using the Modula3 Network Objects package. Network Objects [3] are special Modula 3 objects that support remote access to fields and methods. Obliq uses a Network Object Daemon to make object references publicly available. In Visual Obliq we use this mechanism to make the session constructor publicly available. Any site that starts a Visual Obliq must must ....

Andrew D. Birrell, Greg Nelson, Susan Owicki, and Edward P. Wobber. Network Objects. Proceedings of the 14th ACM Symposium on Operating System Principles, pages 217--130, December 1993.

....standard buffering techniques to improve performance of certain distributed objects. The buffered collection and buffered iterator patterns allow efficient handling of collections of small primitive elements while supporting conventional distributed object semantics through remote proxy objects[3][4]. Specifically, the patterns apply to remote proxies for collections that are composed of very large numbers of small primitive elements in collection form. These patterns are motivated by the need to introduce efficiency to the handling of these small primitive elements without compromising the ....

.... Concrete Aggregate portion of the Itera Passive Server Side Active Client Side BufferedCollection RProxy Input RBuffer Concrete RBuffer Input Buffer Real Collection Concrete Buffer Buffered Collection Proxy tor pattern described in [3] It is also similar to the Network Proxies described in [4]. Buffered Collection RProxy The remote side of the object proxy. This contains the real collection. In general, the names of classes on the remote or server side of the proxy correspond to the name of the client side of the proxy with the R prefix added. Input Buffer RBuffer Buffered ....

[Article contains additional citation context not shown here]

A. Birrell, G. Nelson, S. Owicki, E. Wobber, "Network Objects," Digital Systems Research Center, Feb 1994

....can rebind names. ffl user specified linking: in this case, the user explicitly specifies which names are to be bound to which operations on which sites. An example of this would be the net import( primitive provided by Obliq [4] as well the NetObj.Import primitive provided by Network Objects [3] that has been used to implement it) While this provides the greatest flexibility of all schemes, the programmer can rebind names as and when needed, it requires the user to manage all linking operations. 5 Related work Various forms and implementations of user specified linking have been ....

....Various forms and implementations of user specified linking have been described in the literature. At the simplest level, the eval(env,expr) primitive that has long been available allows the user to control the bindings for the free variables in the expression expr. Obliq [4] and Network Objects [3] allow the programmer to query a name server and obtain a reference which can then be bound to a name in the program. The fragmentedobjects model [17, 18] proposed by Shapiro includes a detailed interface for binding and unbinding references in a distributed system. First class environments [8] ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network objects. In Proceedings of the 14th ACM Symposium on Operating System Principles, pages 217--30, Dec 1993.

....operations: RPC systems (like DCE) always ship the arguments of a function to a remote server. Spring[6] provides some flexibility with subcontracts but the interface presented to an application process is basically still a stub. Remote object systems like, for example CORBA[8] and Network Objects[1] provide the same functionality as an RPC based system: arguments are shipped to the (remote) object. A system that seems at first glance similar to ours is the combination of Fragmented Objects with SSP chains[9] Fragmented Objects, as described in [7] provide a similar model to the user of the ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. "Network Objects." In Proc. 14th Symposium on Operating Systems Principles, pp. 217--230, Asheville, North Carolina, December 1993. ACM.

....Our proxy specialization techniques provide similar structuring opportunities within C at the cost of additional code complexity. Munin [6] specializes proxy objects for portions of memory similar to problem oriented shared memory [8] using a standard communication facility. Network objects [5] provide support for exporting objects including a powerful marshalling system. The system is implemented as a set of simple interfaces, similar in motivation to the channel interface design. However, the network object system does not address functional extensions by applications. Multicast RPC ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network Objects. In Proceedings of the Fourteenth Symposium on Operating Systems Principles. ACM, December 1993.

....middleware solution. However, in comparing middleware solutions, differences exist with respect to interfaces and organization. Interfaces are either expressed in terms of a programming language, or through special interface libraries. Language based interfaces, such as offered by Network Objects [5] have the benefit that they generally support application development at a relatively high level of abstraction. A more restricted use of languages is offered by systems such as Fragmented Objects [11] and Thor [10] in which new object types are to be specified in a special definition language. ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. "Network Objects." In Proc. 14th Symp. on Operating Systems Principles, pp. 217--230, Asheville, NC, Dec. 1993. ACM.

....Work Many object support systems have been designed. Some examples are Emerald [Black87] Cool [Lea93] Guide [Balter91] Spring [Hamilton93b, Radia93] and Choices [Campbell93] However, these systems have not been designed to run on general purpose operating systems. Network Objects system [Birrell93] offers somewhat similar functionality to Shadows but does not support object mobility, a key feature of our system. DC [Schill93] and Panda [Assenmacher93] provide C extensions and run time systems, on top of DCE and a specialised picokernel respectively, which offer similar functionality ....

Birrell, A., G. Nelson, S. Owicki and E. Wobber, "Network Objects", 14th ACM Symposium on Operating System Principles, pp. 217-230, Asheville, North Carolina, December 1993.

....choose to conduct our discussion in the context of RPC, but similar issues arise with the other mechanisms. RPC mechanisms have been built with many different objectives. For example, there are RPC mechanisms designed for heterogeneity [7] performance [3, 28, 18] flexibility [9] or simplicity [5]. Adding persistence to RPC introduces new issues, many of which have been addressed elsewhere [30, 23, 24] In this paper we concentrate on the semantics for parameter passing in a type complete persistent RPC. We use this term to refer to an RPC for a persistent programming language. The next ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network objects. In Proceedingsof the 14th ACM Symposium on Operating Systems Principles, pages 217--230, Dec. 1993.

....communicating continuous data such as voice and video are hardly supported. Operations on remote shared objects. Finally, we distinguish paradigms centered around user defined operations on remote state, such as offered by objects in Corba [11] and Spring [8] and in models such as Network Objects [3]. Solutions that fall within this paradigm implement remote objects, where a distinction is made between clients and servers. Clients issue requests (invoke methods) and servers implement methods and send back replies. This limits communication patterns to the asymmetrical client server model, ....

A. Birrell, G. Nelson, S. Owicki, and E. Wobber. "Network Objects. " In Proc. 14th Symp. on Operating System Principles, pp. 217--230, Asheville, North Carolina, Dec. 1993. ACM.

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A. Birrell, G. Nelson, S. Owicki, E. Wobber, Network objects, in: Symposium on Operating Systems Principles, ACM Press, 1993, pp. 217--230.

No context found.

A. D. Birrell, G. Nelson, S. Owicki, and E. Wobber. Network objects. In Proc. 14th Symposium on Operating Systems Principles, 1993.

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