Topic summary
COM object
Extracted from the Wikipedia article Component Object Model.
Threading
In COM, threading is addressed through a concept known as apartments. An individual COM object lives in exactly one apartment, which might either be single-threaded or multi-threaded. There are three types of apartments in COM: Single-Threaded Apartment (STA), Multi-Threaded Apartment (MTA), and Thread Neutral Apartment (NA). Each apartment represents one mechanism whereby an object's internal state may be synchronized across multiple threads. A process can consist of multiple COM objects, some of which may use STA and others of which may use MTA. All threads accessing COM objects similarly live in one apartment. The choice of apartment for COM objects and threads are determined at run-time, and cannot be changed.