CComSingleThreadModel

CComSingleThreadModel is a threading model class in Microsoft's MFC (Microsoft Foundation Classes) library, designed to manage the synchronization of resources in single-threaded applications. It is part of the COM (Component Object Model) infrastructure and is used to ensure thread safety when dealing with COM objects that may be accessed from multiple threads.

In a single-threaded apartment (STA) model, which is the default threading model for most COM objects, all COM calls are executed in the same thread. CComSingleThreadModel provides mechanisms to enforce this behavior by maintaining a reference count for each COM object. When an object is created, its reference count is incremented, and when it is released, the count is decremented. If an attempt is made to access the object from a different thread, the model ensures that the object remains locked to the original thread, preventing potential race conditions or resource conflicts.

This class is particularly useful in scenarios where COM objects are shared across different parts of an application but must remain thread-safe. By using CComSingleThreadModel, developers can avoid the complexity of manual synchronization while still ensuring that COM objects are accessed in a controlled manner. It is commonly used alongside other MFC COM-related classes, such as CComObjectRootEx, to manage the lifecycle of COM objects.

CComSingleThreadModel is typically initialized in the application's initialization code, often within the InitInstance method of the application's main window class. It is inherited from CComModule, which is responsible for managing COM registration and other COM-related tasks. While it enforces thread safety, it does not inherently prevent all threading issues, so developers should still exercise caution when dealing with shared resources outside the COM object model.