C# in a Nutshell, Second Edition

COM+ Support

The CLR also includes special plumbing and interop services that allow CLR classes to be deployed as COM+ configured components. This allows both CLR clients and classic COM clients to make use of COM+ services for building scalable applications.

What Is COM+?

COM+ provides a set of services that are designed to help build scalable distributed systems, such as distributed transaction support, object pooling, Just-In-Time activation, synchronization, role-based security, loosely coupled events, and others.

These services are provided by a runtime environment called the COM+ runtime, and are based on the idea of intercepting new COM object creation and (possibly) method calls to layer in the additional services as needed.

COM classes that use COM+ services are called Configured Components because the exact set of services each COM class requires is controlled and configured using declarative attributes that are stored in a metadata repository called the COM+ Catalog.

The COM+ Catalog groups a set of configured components together into something called an Application, which also has metadata settings that control which process the COM components end up in when they are created at runtime (the options here are Library and Server, where Library components end up in the creator’s process, while Server components are hosted in a separate process), the security principal the new process runs as, and other settings.

Using COM+ Services with CLR Classes

Naturally, CLR classes can