The Uninstall_Init function prototype is called before the uninstallation begins. This function can be used for custom operations such as closing the application if it is running.
codeUNINSTALL_INIT Uninstall_Init(HWND hwndParent, LPCTSTR pszInstallDir);
The Uninstall_Init function prototype is part of Setup.dll, an ISV-created file for custom operations dealing with installation and uninstallation of applications.