DllCanUnloadNow  NR3B2O

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

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

STDAPI DllCanUnloadNow();

Return Values

S_OK

The DLL can be unloaded.

S_FALSE

The DLL cannot be unloaded now.

Remarks

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 CoFreeUnusedLibrariesKKW0B9 function. When it returns S_OK, CoFreeUnusedLibraries safely frees the DLL.

Notes to Implementers

You need to implement DllCanUnloadNow in, and export it from, DLLs that are to be dynamically loaded through a call to the CoGetClassObject2_47ZR8 function. (You also need to implement and export the DllGetClassObject14W.OVW 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 CoUninitializeITVXER function to release the OLE libraries.

If the DLL links to another DLL, returning S_OK from DllCanUnloadNow will also cause the second, dependent DLL to be unloaded. To eliminate the possibility of a crash, the primary DLL should call the CoLoadLibrary2APZM3O function, specifying the path to the second DLL as the first parameter, and setting the auto free parameter to TRUE. This forces the COM library to reload the second DLL and set it up for a call to CoFreeUnusedLibrariesKKW0B9 to free it separately when appropriate.

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

See Also