I am assuming it does but would appreciate confirmation of this from someone knowledgable! Ive seen a similar thread but no explicit confirmation.
Standard COM rules dictate that if you want to see if 2 interfaces belong to the same object, you query IUknown from each interface and then compare the 2 IUknown pointers. If pUnknown1==pUnknown2 they are the same object.
Does this still hold across process boundaries after the interfaces have been marshalled several times?
For example, take 3 out-of-process COM servers:
ObjectContainer.exe
ObjectRouter.exe
ObjectComparer.exe
OBJECTCOMPARER.EXE
This implements an interface called IObjectComparer which supports the following functions:
* HRESULT SetObject1(ITestObject obj1)
* HRESULT SetObject2(ITestObject obj2)
* HRESULT CompareSetObjects(BOOL* bEqual)
OBJECTROUTER.EXE
This implements IObjectRouter which has a single function:
* SetObject2OnComparer(ITest
All this does is to call SetObject2() in ObjectComparer.exe with the passed parameter.
OBJECTCONTAINER.EXE
This maintains a single instance of CTestObject (which implements ITestObject).
It calls SetObject1() on IObjectComparer with the CTestObject
It then calls SetObject2OnComparer() with the same CTestObject
It then calls CompareSetObjects()
Should CompareSetObject() still be able to query IUnknown from obj1 and obj2 and compare the pointer value, even though they have been marshalled several times?
Presumably the proxy/stub code is intelligent enough to supply the same pointer values for the single instance of the out-of-process object?
Many thanks!
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I would agree with evilrix. My understanding is probably more limited than his, but this I believes confirms it as well.
"The COM specification states that a client calling QueryInterface(IID_IUnknow
--http://www.usenix.org/ev
Key words: must always!
Regards,
isa
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by: evilrixPosted on 2009-08-20 at 06:44:04ID: 25142398
>> Does the COM object IUnknown equality comparison work across process boundaries?
It's been a while and I'd have to check to be 100% sure but IIRC a correctly written COM component, when comparing the IUnknown Interfaces must correctly identify components that are the same or different and this is true even for out-of-process components. Also, IIRC this is ONLY true when comparing via the IUnknown interfaces.
This seems to confirm: http://tinyurl.com/nzqve3