AfxOleLockApp and AfxOleUnlockApp

The Microsoft Foundation Class Library provides additional facilities for controlling application behavior when external clients have references to the application's objects. Besides maintaining a count of references to each object, servers maintain a global count of active objects. The global functions AfxOleLockApp and AfxOleUnlockApp update the application's count of active objects. If this count is nonzero, the application does not terminate when the user chooses Close from the system menu or Exit from the File menu. Instead, the application's main window is hidden (but not destroyed) until all pending client requests have been completed. Typically, AfxOleLockApp and AfxOleUnlockApp are called in the constructors and destructors, respectively, of classes that support Automation.

FROM : MSDN