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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Distributed object</span></span>

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<p>In <a href="Distributed_computing" title="Distributed computing">distributed computing</a>, <b>distributed objects</b> are objects (in the sense of <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented programming</a>) that are distributed across different <a href="Address_space" title="Address space">address spaces</a>, either in different <a href="Process_(computing)" title="Process (computing)">processes</a> on the same computer, or even in multiple <a href="Computer" title="Computer">computers</a> connected via a <a href="Computer_network" title="Computer network">network</a>, but which work together by sharing data and invoking methods. This often involves <a href="Location_transparency" title="Location transparency">location transparency</a>, where remote objects appear the same as local objects. The main method of <a href="Distributed_object_communication" title="Distributed object communication">distributed object communication</a> is with <a href="Remote_method_invocation" class="mw-redirect" title="Remote method invocation">remote method invocation</a>, 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.

</p><p>Distributed objects were popular in the late 1990s and early 2000s, but have since fallen out of favor.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p><p>The term may also generally refer to one of the extensions of the basic <a href="Object_(computer_science)" title="Object (computer science)">object</a> concept used in the context of distributed computing, such as <i>replicated objects</i> or <i>live distributed objects</i>.

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<ul><li><i><a href="Replication_(computer_science)" class="mw-redirect" title="Replication (computer science)">Replicated objects</a></i> are groups of software components (<i>replicas</i>) 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 <i>object</i> reflects the fact that interacting with any of them exposes the same externally visible state and behavior.</li>

<li><i><a href="Live_distributed_object" title="Live distributed object">Live distributed objects</a></i> (or simply <i><a href="Live_distributed_object" title="Live distributed object">live objects</a></i>)<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> generalize the <i>replicated object</i> 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 a distinct identity, and that can encapsulate distributed state and behavior.</li></ul>

<p>See also <a href="Internet_protocol_suite" title="Internet protocol suite">Internet protocol suite</a>.

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<div class="mw-heading mw-heading2"><h2 id="Local_vs._distributed_objects">Local vs. distributed objects</h2></div>

<p>Local and distributed objects differ in many respects.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Here are some of them:

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<ol><li>Life cycle : Creation, migration and deletion of distributed objects is different from local objects</li>

<li>Reference : Remote references to distributed objects are more complex than simple pointers to memory addresses</li>

<li>Request Latency : A distributed object request is orders of magnitude slower than local method invocation</li>

<li>Object Activation : Distributed objects may not always be available to serve an object request at any point in time</li>

<li>Parallelism : Distributed objects may be executed in parallel.</li>

<li>Communication : There are different communication primitives available for distributed objects requests</li>

<li>Failure : Distributed objects have far more points of failure than typical local objects.</li>

<li>Security : Distribution makes them vulnerable to attack.</li></ol>

<div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2></div>

<p>The RPC facilities of the cross platform serialization protocol, <a href="Cap'n_Proto" title="Cap'n Proto">Cap'n Proto</a> 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/<a href="Capability-based_security" title="Capability-based security">capabilities</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>

</p><p>Distributed objects are implemented in <a href="Objective-C" title="Objective-C">Objective-C</a> using the <a href="Cocoa_(API)" title="Cocoa (API)">Cocoa API</a> with the NSConnection class and supporting objects.

</p><p>Distributed objects are used in <a href="Java_RMI" class="mw-redirect" title="Java RMI">Java RMI</a>.

</p><p><a href="CORBA" class="mw-redirect" title="CORBA">CORBA</a> lets one build distributed mixed object systems.

</p><p><a href="Distributed_Component_Object_Model" title="Distributed Component Object Model">DCOM</a> is a framework for distributed objects on the Microsoft platform.

</p><p><a href="DDObjects" title="DDObjects">DDObjects</a> is a framework for distributed objects using Borland Delphi.

</p><p>Jt is a framework for distributed components using a messaging paradigm.

</p><p><a href="JavaSpaces" class="mw-redirect" title="JavaSpaces">JavaSpaces</a> is a Sun specification for a distributed, shared memory (space based)

</p><p>Pyro is a framework for distributed objects using the <a href="Python_(programming_language)" title="Python (programming language)">Python programming language</a>.

</p><p>Distributed Ruby (DRb) is a framework for distributed objects using the <a href="Ruby_programming_language" class="mw-redirect" title="Ruby programming language">Ruby programming language</a>.

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<ul><li><a href="Fragmented_object" title="Fragmented object">Fragmented object</a></li>

<li><a href="Distributed_object_communication" title="Distributed object communication">Distributed object communication</a></li>

<li><a href="Object_request_broker" title="Object request broker">Object request broker</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://martinfowler.com/articles/distributed-objects-microservices.html">Microservices and the First Law of Distributed Objects</a>, Martin Fowler, 13 August 2014</span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Ostrowski, K., Birman, K., Dolev, D., and Ahnn, J. (2008). "Programming with Live Distributed Objects", <i>Proceedings of the 22nd European Conference on Object-Oriented Programming</i>, Paphos, Cyprus, July 07–11, 2008, J. Vitek, Ed., <i>Lecture Notes in Computer Science</i>, vol. 5142, Springer-Verlag, Berlin, Heidelberg, 463-489, <a rel="nofollow" class="external free" href="http://portal.acm.org/citation.cfm?id=1428508.1428536">http://portal.acm.org/citation.cfm?id=1428508.1428536</a>.</span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">W. Emmerich (2000) Engineering distributed objects, John Wiley & Sons Ltd.</span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text">Samuel C. Kendall, <a href="Jim_Waldo" title="Jim Waldo">Jim Waldo</a>, Ann Wollrath, and Geoff Wyant. 1994. A Note on Distributed Computing. Technical Report. Sun Microsystems, Inc., Mountain View, CA, USA.</span>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://kentonv.github.io/capnproto/rpc.html">"Cap'n Proto: RPC Protocol"</a>.</cite></span>

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