DllCanUnloadNow function (combaseapi.h)

Determines whether the DLL that implements this function is in use. If not, the caller can unload the DLL from memory.

OLE does not provide this function. DLLs that support the OLE Component Object Model (COM) should implement and export DllCanUnloadNow.


HRESULT DllCanUnloadNow();

Return value

If the function succeeds, the return value is S_OK. Otherwise, it is S_FALSE.


A call to DllCanUnloadNow determines whether the DLL from which it is exported is still in use. A DLL is no longer in use when it is not managing any existing objects (the reference count on all of its objects is 0).

Notes to Callers

You should not have to call DllCanUnloadNow directly. OLE calls it only through a call to the CoFreeUnusedLibraries function. When it returns S_OK, CoFreeUnusedLibraries frees the DLL.

Notes to Implementers

You must implement DllCanUnloadNow in, and export it from, DLLs that are to be dynamically loaded through a call to the CoGetClassObject function. (You also need to implement and export the DllGetClassObject function in the same DLL).

If a DLL loaded through a call to CoGetClassObject fails to export DllCanUnloadNow, the DLL will not be unloaded until the application calls the CoUninitialize function to release the OLE libraries.

DllCanUnloadNow should return S_FALSE if there are any existing references to objects that the DLL manages.


Requirement Value
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header combaseapi.h (include Objbase.h)

See also