Xerces-C in a COM object for ASP

["Stratton, Jason" <js...@telegea.com>]

I have an interesting/frustrating situation occurring.

I have created a COM object which is used by an ASP. In a method of the COM
object a XML transaction occurs and I need to parse the response. I have
chosen to use Xerces-C for this task. I got it set up and working fine. But
the second time the method is called, it crashes when instantiating the
Xerces-C parser. I thought this was odd, but while playing with it for a
while, I resolved it by using a static instance of the parser. (Effectively
creating it only once.) This works fine. I can call the method multiple
times without a problem. It feels like a hack, but I can live with it.

Now I needed to create another, similar COM object to be used in a different
ASP. For parsing the XML, I use exactly the same code, the same C++ file in
fact. So the same code is compiled and statically linked into two different
COM objects. Again, this appears to work just fine ... until I attempt to
instantiate both COM objects at the same time.

I visit the first ASP and make the transaction successfully, then visit the
second ASP and when I try to kick off the transaction, it crashes when
attempting to instantiate the Xerces-C parser. The same thing happens when
visiting the pages in the opposite order, second ASP then the first will
crash.

It appears that at most only one Xerces-C parser may be created at any point
in time. Is this correct? Is there something important that I am missing?

The code I have written for using Xerces-C is below. Any help will be
greatly appreciated.

Thank you.
Jason Stratton
jstratton@telegea.com


Here is my code. I have cut out & commented the irrelevant parts. I have
also noted where the crashing occurs.

HRESULT TGRTITransaction::ParseXMLResponse(BSTR bstrOutBuf /*other param*/)
{
	// <snip> validating param

	// The response is coming back as UTF-8, but as Unicode.
	// So we must convert the Unicode to single byte char string.
	// (Or we could find the UTF-8 in the string and change it to
"UTF-16")
	int isbXMLLength = wcslen(bstrOutBuf)*sizeof(wchar_t);
	char *psbXML = new char[isbXMLLength];
	if (!psbXML)
		;// report error & return
	BSTR_TO_STRING(bstrOutBuf, psbXML, isbXMLLength);

	try
	{
		 XMLPlatformUtils::Initialize();
	}
	catch (const XMLException& e)
	{
		// report error
		return E_FAIL;
	}

	static DOMParser parser;	// if not static, will crash second
time thru - I don't know why

	parser.setDoValidation(false);
	parser.setDoNamespaces(false);
	TGXMLErrorHandler errorHandler(/*param*/);
	parser.setErrorHandler(&errorHandler);
	parser.setExpandEntityReferences(true);
	parser.setToCreateXMLDeclTypeNode(true);

	static const char*  BufId = "LiveOakXMLResponse";
	MemBufInputSource memBufIS((const XMLByte*)psbXML, isbXMLLength,
BufId, false);

	try
	{
		parser.parse(memBufIS);
	}
	catch (const XMLException& e)
	{
		// report error
		delete[] psbXML;
		XMLPlatformUtils::Terminate();
		return E_FAIL;
	}

	DOM_Document doc = parser.getDocument();
	hr = TraverseDOM(doc /*other param*/);

	delete[] psbXML;

	XMLPlatformUtils::Terminate();

	return hr;
}

Re: Xerces-C in a COM object for ASP

[Simon Fell <so...@zaks.demon.co.uk>]

you should call XMLPlatformUtils::Initialize & Terminate once per
process, not per call. Move the XMLPlatformUtils::Initialize /
Terminate to ObjectMain (I'm assuming you're using ATL), and then go
back to creating a parser per request.

Cheers
Simon

On Thu, 28 Sep 2000 14:50:08 -0400, in soap you wrote:

>I have an interesting/frustrating situation occurring.
>
>I have created a COM object which is used by an ASP. In a method of the COM
>object a XML transaction occurs and I need to parse the response. I have
>chosen to use Xerces-C for this task. I got it set up and working fine. But
>the second time the method is called, it crashes when instantiating the
>Xerces-C parser. I thought this was odd, but while playing with it for a
>while, I resolved it by using a static instance of the parser. (Effectively
>creating it only once.) This works fine. I can call the method multiple
>times without a problem. It feels like a hack, but I can live with it.
>
>Now I needed to create another, similar COM object to be used in a different
>ASP. For parsing the XML, I use exactly the same code, the same C++ file in
>fact. So the same code is compiled and statically linked into two different
>COM objects. Again, this appears to work just fine ... until I attempt to
>instantiate both COM objects at the same time.
>
>I visit the first ASP and make the transaction successfully, then visit the
>second ASP and when I try to kick off the transaction, it crashes when
>attempting to instantiate the Xerces-C parser. The same thing happens when
>visiting the pages in the opposite order, second ASP then the first will
>crash.
>
>It appears that at most only one Xerces-C parser may be created at any point
>in time. Is this correct? Is there something important that I am missing?
>
>The code I have written for using Xerces-C is below. Any help will be
>greatly appreciated.
>
>Thank you.
>Jason Stratton
>jstratton@telegea.com
>
>
>Here is my code. I have cut out & commented the irrelevant parts. I have
>also noted where the crashing occurs.
>
>HRESULT TGRTITransaction::ParseXMLResponse(BSTR bstrOutBuf /*other param*/)
>{
>	// <snip> validating param
>
>	// The response is coming back as UTF-8, but as Unicode.
>	// So we must convert the Unicode to single byte char string.
>	// (Or we could find the UTF-8 in the string and change it to
>"UTF-16")
>	int isbXMLLength = wcslen(bstrOutBuf)*sizeof(wchar_t);
>	char *psbXML = new char[isbXMLLength];
>	if (!psbXML)
>		;// report error & return
>	BSTR_TO_STRING(bstrOutBuf, psbXML, isbXMLLength);
>
>	try
>	{
>		 XMLPlatformUtils::Initialize();
>	}
>	catch (const XMLException& e)
>	{
>		// report error
>		return E_FAIL;
>	}
>
>	static DOMParser parser;	// if not static, will crash second
>time thru - I don't know why
>
>	parser.setDoValidation(false);
>	parser.setDoNamespaces(false);
>	TGXMLErrorHandler errorHandler(/*param*/);
>	parser.setErrorHandler(&errorHandler);
>	parser.setExpandEntityReferences(true);
>	parser.setToCreateXMLDeclTypeNode(true);
>
>	static const char*  BufId = "LiveOakXMLResponse";
>	MemBufInputSource memBufIS((const XMLByte*)psbXML, isbXMLLength,
>BufId, false);
>
>	try
>	{
>		parser.parse(memBufIS);
>	}
>	catch (const XMLException& e)
>	{
>		// report error
>		delete[] psbXML;
>		XMLPlatformUtils::Terminate();
>		return E_FAIL;
>	}
>
>	DOM_Document doc = parser.getDocument();
>	hr = TraverseDOM(doc /*other param*/);
>
>	delete[] psbXML;
>
>	XMLPlatformUtils::Terminate();
>
>	return hr;
>}
>
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