smli_tr-94-29 - A Note on Distributed Computing Jim Waldo...

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Unformatted text preview: A Note on Distributed Computing Jim Waldo Geoff Wyant Ann Wollrath Sam Kendall SMLI TR-94-29 November 1994 Abstract: We argue that objects that interact in a distributed system need to be dealt with in ways that are intrinsically different from objects that interact in a single address space. These differences are required because distributed systems require that the programmer be aware of latency, have a dif- ferent model of memory access, and take into account issues of concurrency and partial failure. We look at a number of distributed systems that have attempted to paper over the distinction between local and remote objects, and show that such systems fail to support basic requirements of robustness and reliability. These failures have been masked in the past by the small size of the distributed systems that have been built. In the enterprise-wide distributed systems foreseen in the near future, however, such a masking will be impossible. We conclude by discussing what is required of both systems-level and application-level program- mers and designers if one is to take distribution seriously. A Sun Microsystems, Inc. Business M/S 29-01 2550 Garcia Avenue Mountain View, CA 94043 email addresses: jim.waldo@east.sun.com geoff.wyant@east.sun.com ann.wollrath@east.sun.com sam.kendall@east.sun.com 2 A Note on Distributed Computing Jim Waldo, Geoff Wyant, Ann Wollrath, and Sam Kendall Sun Microsystems Laboratories 2550 Garcia Avenue Mountain View, CA 94043 1 Introduction Much of the current work in distributed, object-oriented systems is based on the assumption that objects form a sin- gle ontological class. This class consists of all entities that can be fully described by the specification of the set of interfaces supported by the object and the semantics of the operations in those interfaces. The class includes objects that share a single address space, objects that are in sepa- rate address spaces on the same machine, and objects that are in separate address spaces on different machines (with, perhaps, different architectures). On the view that all objects are essentially the same kind of entity, these differ- ences in relative location are merely an aspect of the implementation of the object. Indeed, the location of an object may change over time, as an object migrates from one machine to another or the implementation of the object changes. It is the thesis of this note that this unified view of objects is mistaken. There are fundamental differences between the interactions of distributed objects and the interactions of non-distributed objects. Further, work in distributed object-oriented systems that is based on a model that ignores or denies these differences is doomed to failure, and could easily lead to an industry-wide rejection of the notion of distributed object-based systems....
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This note was uploaded on 11/15/2011 for the course ECKOW 123 taught by Professor Riuyt during the Spring '11 term at University of Damascus.

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smli_tr-94-29 - A Note on Distributed Computing Jim Waldo...

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