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Documentation

Overall Architecture

Facade pattern. Instances of MpMiddleware are facade objects. A middleware is made of parts. Each part knows about the middleware it belongs to, so it can retrieve other parts if needed. MpMiddleware is abstract. We create middleware as instances of its concrete subclasses. Example of creating a middleware on top of TCP/IP. The initialization of the middleware takes care of setting up all parts.

middleware := MpTcpMiddleware new.

Exporting objects

A middleware can export an object. That is making it available remotely. Exporting an object answers a remote reference instance of MpRemoteReference Example

someObject := ...
remoteReference := middleware export: someObject.

See MpMiddlewareTest>>#testExportObject.

Proxy creation

Proxies can be forged by the middleware user from a remote reference. As in the following example :

remoteReference := middlewareA export: self newValueHolder.
proxy := middlewareB objectAt: remoteReference.

Proxies are automatically created upon receiving a message which some argument is a remote reference, or upon receiving a remote reference as an answer to a sent message.

objectFromA := …
remoteReferenceA := middlewareA export: objectFromA.
proxyAInB := middlewareB objectAt: remoteReferenceA.
objectFromB := …
proxyAInB doSomethingWith: objectFromB.

A proxy on objectFromB is created on the fly by middlewareA upon receiving themessage doSomethingWith:.

Each exported object is assigned an ID. By default, this is automated. But, IDs can be set by the middleware user upon exporting.

middlewareA export: exportedObject id: #someUniqueID.
remoteReference := MpRemoteReference
                           address: middlewareA address
                           objectId: #someUniqueID.
proxy := middlewareB objectAt: remoteReference.

Proxy Class and Species

We assume that classes that have the same name are interoperable. This asumption is useful for instnce, when it comes to testing equality. So, when we send a proxy the class or the species message, we get a class from the local image (the one where the message was issued), if there is one with the same name as the actual remote class.

objectFromA := #(1 2 3).
remoteReferenceA := middlewareA export: objectFromA.
proxyAInB := middlewareB objectAt: remoteReferenceA.
proxyAInB class. "--> actual Array class in B"
proxyAInB species. "--> actual Array class in B"