This function determines whether the dynamic-link library (DLL) that implements this function is in use. If it is not, the caller can safely 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.|
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, that is, when the reference count on all of its objects is zero.
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 safely frees the DLL.
You need to 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.
If the DLL links to another DLL and DllCanUnloadNow returns S_OK, the primary and the dependent DLL will be unloaded. To eliminate the possibility of a crash, the primary DLL should call the CoLoadLibrary 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 CoFreeUnusedLibraries to free it separately when appropriate.
DllCanUnloadNow should return S_FALSE if there are any existing references to objects that the DLL manages.
To determine whether the platform supports this function, see Determining Supported COM APIs.