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Can't access MS XML DOM once passed across a DCOM boundary ?

Posted on 2002-04-19
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Last Modified: 2008-02-01
I'm using C++ (but it's not a C++ problem) with the MS XML DOM in order to build well formed XML data files and apply XSLT to these to get nice output. That all works fine. However when I try to pass the DOM Interface across to another DCOM object I've defined (an optional component) and access it this causes an exception -

First-chance exception in MSServer.exe (KERNEL32.DLL): 0xC0010000: (no name).
First-chance exception in MSServer.exe (KERNEL32.DLL): 0xE06D7363: Microsoft C++ Exception.

The Microsoft support knowledgebase has the following to say -

http://support.microsoft.com/default.aspx?scid=kb;EN-US;q259004

Which isn't solving the proble at all, it's just sweeping it under the carpet ... I can't believe it's not possible to pass an XML DOM interface across to another DCOM component and use it from there, that's the whole point of DCOM really !

Any insights anyone ?
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Question by:s_stirley
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Expert Comment

by:b1xml2
ID: 6954432
We have had this chat with Microsoft Premier Support and all they can say is that:

1. Do not pass DOM objects by reference or even by value across DCOM Objects. Pass XML String.

2. This problem relates to context switching and loss of pointers.

and thus this is the same thing in the URL mentioned:

>>
If you want to use XML across execution contexts, define a method on your wrappers that passes the raw XML data back to the caller (which you obtain through the use of IXMLDOMDocument::get_XML()). The caller can then call IXMLDOMDocument::loadXML(BSTR) on this string to restore the XML object locally.
<<
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Expert Comment

by:b1xml2
ID: 6954441
or rather the pointers are no longer valid references
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Accepted Solution

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BigRat earned 300 total points
ID: 6962412
"I can't believe it's not possible to pass an XML DOM interface across to another DCOM component and use it from there, that's the whole point of DCOM really !"

The XML DOM may be declared as an interface but it is actually an in-process object.

In DCOM you can get objects to source and sink themselves only if the support certain types of marshalling and, most importantly, they run in their own process space - called the threading model. In which case proxy objects actually do the work in passing the parameters and returning the result with little messages.

There is a very readable book "Learning DCOM" from O'Reilly which explains exactly how this all works, including the delta pings and all the other nasty complexities.

As Brandon says get the DOM to XML source in a BSTR and just pass that along. The time taken to destruct and construct the DOM will be negligable compared to the DCOM message passing.

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Author Comment

by:s_stirley
ID: 6962859
Using get_xml sending it across as a BSTR and then reloading that to another DOM in the client does work fine, and is quite quick.

Seems a shame I can't pass the object, but that's life sometimes ! thanks for both answers, I'd split the points but it won't let me :(  they go to BigRat for the in-depth reason why it won't work and the book suggestion.

Thanks.
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