Determines whether the DLL that implements it is in use. It is called by OLE,
not by the application. If the DLL is not in use, the calling function can safely
unload it from memory.
OLE does not provide this function. DLLs that support the OLE Component
Object Model(COM) should implement and export DllCanUnloadNow
Indicates that the DLL can be unloaded.
Indicates that the DLL cannot be unloaded now.
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
safely frees the DLL.
Notes to Implementors
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 by 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, returning S_OK from DllCanUnloadNow
will also cause the second, dependent DLL to be unloaded. To eliminate the
possibility of a crash, the DLL should call the CoLoadLibrary
, TRUE), which forces the COM library to reload the second DLL and set it up
for a call to CoFreeUnusedLibraries
to free it separately when appropriate.
should return S_FALSE if there are any existing references to objects that
the DLL manages.
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