COM

Not really, as COM/DCOM interfaces use pointers to functions, just as a typical class might (not a real COM object):

class IMyClass : public IUnknown
{
public:
IMyClass();
HRESULT (*MyFunction)();
};

When you create an IMyClass object, the COM server checks if it''s the first instance, and if so, it loads the .DLL file that contains the functions. It then sets its function pointers (MyFunction for example) to point to the DLL code.

quote:

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Original post by walkingcarcass
i dont know a lot about the internals of COM calls but i understand they use lookup tables, call into DLLs and are SLOW!

is there an easy way to get the DLL function pointer to speed up calls? how many cycles would it save?

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You are describing IDispatch - the dynamic-binding/OLE Automation aspect of COM, and it is slow.

Most of the time you use vtable binding, which is slower than inlined code, but the cost of dereferencing the vtable and jumping is mitigated on modern x86 processors, as they can perform the dereferencing and vectoring in the same op code.

The only time you pay a serious penalty, is if jumping to the code results in a hard or soft page-fault - which is no different than a normal function call.

Default creation of COM objects is god-awfully slow becase CoCreate looks up a pile of crap in the registery.

P.S. DirectX uses COM.

quote:

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Original post by Magmai Kai Holmlor
P.S. DirectX uses COM.

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If you take a look at which forum he posted in, I think it''s pretty safe to say he already knew that

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The world holds two classes of men -- intelligent men without religion, and religious men without intelligence. - Abu''l-Ala-Al-Ma''arri (973-1057; Syrian poet)

i dont know anything about IDispatch but can i just gather the function pointers of all COM functions i intend to use?

Magmai Kai Holmlor, do you mean "CALL dword ptr [lookuplable+[functionID]]" is a legal instruction?

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Sure you can. You can query for the functions and cache the results.

But why - nearly ALL classes that implement IDispatch also implement a "sensible interface".


Regards

Thomas Tomiczek
THONA Consulting Ltd.
(Microsoft MVP C#/.NET)