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COM & .NET Component Services by Juval Lowy

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Chapter 2. COM+ Context

COM+ provides services to components by intercepting the calls the client makes to component interfaces. The idea of providing services through an interception mechanism is not a COM+ innovation. As you will see, classic COM also provides component services via interception. What is new is the length to which COM+ takes the idea. This chapter starts by describing the way classic COM uses marshaling to provide its services and to encapsulate the runtime requirements of its objects. Next, the chapter introduces you to the COM+ context—the innermost execution scope of an object. COM+ call interception occurs at context boundaries. Generally, you need not be concerned with contexts at all. They are transparent to you, whether you develop a client or a component. However, the COM+ context is a good model for explaining the way COM+ services are implemented. This book clearly outlines the few cases when you should interact with the contexts directly. Interaction with the contexts occurs mostly when dealing with COM+ instance management and transactions, but also when dealing with some security issues.

Encapsulation via Marshaling in COM

One of the core principles of classic COM is location transparency. Location transparency allows the client code to be independent of the actual object’s location. Nothing in the client’s code pertains to where the object executes, although the client can insist on a specific location as well. A client CoCreates its objects and ...

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