Distributed object: Difference between revisions

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[[File:Distributed object communication.png|thumb|Image describes communication between distributed objects residing in different machines.]]

In [[distributed computing]], '''distributed objects'''{{citationneededcitation needed|date=May 2016}} are objects (in the sense of [[object-oriented programming]]) that are distributed across different [[address space]]s, either in different [[Process (computing)|processes]] on the same computer, or even in multiple [[computer]]s connected via a [[Computer network|network]], but which work together by sharing data and invoking methods. This often involves [[___location transparency]], where remote objects appear the same as local objects. The main method of [[distributed object communication]] is with [[remote method invocation]], generally by message-passing: one object sends a message to another object in a remote machine or process to perform some task. The results are sent back to the calling object.

Distributed objects were popular in the late 1990s and early 2000s, but have since fallen out of favor.<ref>[http://martinfowler.com/articles/distributed-objects-microservices.html Microservices and the First Law of Distributed Objects], Martin Fowler, 13 August 2014</ref>

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The term may also generally refer to one of the extensions of the basic [[object (computer science)|object]] concept used in the context of distributed computing, such as ''replicated objects'' or ''live distributed objects''.

* ''[[replication (computer science)|Replicated objects]]'' are groups of software components (''replicas'') that run a distributed multi-party protocol to achieve a high degree of consistency between their internal states, and that respond to requests in a coordinated manner. Referring to the group of replicas jointly as an ''object'' reflects the fact that interacting with any of them exposes the same externally visible state and behavior.

* ''[[Live distributed object]]s'' (or simply ''[[live distributed object|live objects]]'')<ref>Ostrowski, K., Birman, K., Dolev, D., and Ahnn, J. (2008). "Programming with Live Distributed Objects", ''Proceedings of the 22nd European Conference on Object-Oriented Programming'', Paphos, Cyprus, July 07–11, 2008, J. Vitek, Ed., ''Lecture Notes Inin Computer Science'', vol. 5142, Springer-Verlag, Berlin, Heidelberg, 463-489, http://portal.acm.org/citation.cfm?id=1428508.1428536.</ref> generalize the ''replicated object'' concept to groups of replicas that might internally use any distributed protocol, perhaps resulting in only a weak consistency between their local states. Live distributed objects can also be defined as running instances of distributed multi-party protocols, viewed from the object-oriented perspective as entities that have distinct identity, and that can encapsulate distributed state and behavior.

See also [[Internet protocol suite]].

== Local vs Distributed Objects ==

Local and distributed objects differ in many respects.<ref>W. Emmerich (2000) Engineering distributed objects, John Wiley & Sons Ltd.</ref> <ref>Samuel C. Kendall, Jim Waldo, Ann Wollrath, and Geoff Wyant. 1994. A Note on Distributed Computing. Technical Report. Sun Microsystems, Inc., Mountain View, CA, USA.</ref> Here are some of them:

# Life cycle : Creation, migration and deletion of distributed objects is different from local objects

# Reference : Remote references to distributed objects are more complex than simple pointers to memory addresses

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== Examples ==

The RPC facilities of the cross platform serialization protocol, [[Cap'n Proto]] amount to a distributed object protocol. Distributed object method calls can be executed(chained, in a single network request, if needs be) through interface references/[[Capability-based_securitybased security|capabilities]].<ref>https://kentonv.github.io/capnproto/rpc.html</ref>

Distributed objects are implemented in [[Objective-C]] using the [[Cocoa (API)|Cocoa API]] with the NSConnection class and supporting objects.