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Asynchronous Interface Implementations

Note the following findings about asynchronous interfaces :

1. An interface that is marked to be asynchronous must be derived from IUnknown. It cannot be derived from IDispatch.

2. A C++/ATL implementation which has #import'ed the originating IDL may experience compilation errors e.g. "MIDL2320 : conflicting optimization requirements, cannot optimize : [Procedure '...']" :

2.1 The cause of the problem has to do with the fact that the asynchronous interface most likely was declared outside of the "library" statement in its original IDL file.

2.2 This indicates to the compiler (compiling the current implementation) that the asynchronous interface will not be using Type Library marshaling (i.e. standard marshaling that uses the Type Library for information instead of any proxy/stub DLL).

2.3 The marshaling for the asynchronous interface will be done via a proxy/stub DLL.

2.4 We currently do not why the compilation error is issued. However, we do have a soluton : place an "importlib" statement inside the "library" statement of the current implementation. It must import the type library of the original IDL file.

2.5 This will avert the compilation problem.

3. A good news about asynchronous interfaces is that it can be implemented in VB. However, the VB implementation must be ActiveX EXE based.

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