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- | ===== Ambient References ===== | ||
- | {{ ambientrefs.jpg }} | ||
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- | Ambient references are a novel remote object reference mechanism. Remote object references are " | ||
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- | == Motivation == | ||
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- | One may wonder why new referencing abstractions are required for mobile networks. In order to motivate the need for new referencing abstractions at the language level, we list a number of desirable properties of remote references for mobile networks which current remote referencing abstractions do not offer: | ||
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- | - **Provisional References**: | ||
- | - **Resilience to Partial Failure**: remote references for mobile networks should be able to tolerate network disconnections because of the volatile connnections hardware phenomenon of mobile networks. | ||
- | - **Transitory Addressing**: | ||
- | - **Group Communication**: | ||
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- | == Design == | ||
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- | Ambient references unify two concepts: they are both a peer-to-peer discovery channel //and// an asynchronous communication channel to a remote object. When an ambient reference is **unbound** (i.e. it is a dangling pointer), it is acting as a discovery channel, actively looking for remote service objects in the environment to bind to. Once such a suitable ((What exactly constitutes a " | ||
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- | When the service object to which an ambient reference is bound moves out of communication range, the ambient reference can become unbound again. It becomes a dangling pointer anew and immediately becomes a peer discovery mechanism again: the ambient reference will try to //rebind// to the same or another matching service. | ||
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- | === Describing services === | ||
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- | An ambient reference is always initialized with a //service type// which denotes remote objects intensionally by the service it provides. One may, for example, declare an ambient reference to a nearby printer: | ||
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- | <code javascript> | ||
- | printer = ambient Printer; | ||
- | </ | ||
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- | The code excerpt above creates an ambient reference to an object providing the '' | ||
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- | The primary advantage of using such service types rather than e.g. name servers, IP addresses or URLs is, evidently, abstraction over the machine address of the host providing the services. Ambient references can be used to refer to service objects, the host address of which is unknown to the code declaring the reference. All that needs to be agreed upon is a matching service type. | ||
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- | === Communicating with services === | ||
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- | Asynchronous messages may be sent to an ambient reference at any point in time. For example, in order to print a document on a nearby printer, the '' | ||
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- | <code javascript> | ||
- | printer< | ||
- | </ | ||
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- | In this example code ''< | ||
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- | One may wonder how return values can be acquired from such asynchronous message sends. We use the concept of a **future**, which is a very well known concept that unifies asynchronous message passing with return values. More specifically, | ||
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- | <code javascript> | ||
- | answer = printer< | ||
- | when(answer) lambda(ok) -> { | ||
- | if (ok) | ||
- | print(" | ||
- | } | ||
- | </ | ||
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- | == Example Usage == | ||
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- | == Implementation == | ||
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- | A detailed explanation of ambient references can be found in [[ftp:// | ||
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- | == Further Reading == | ||
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- | Ambient References: Addressing Objects in Mobile Networks. Tom Van Cutsem, Jessie Dedecker, Stijn Mostinckx, Elisa Gonzalez Boix, Theo D' | ||
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- | Also see the [[research: |