Re: DTD caching problems

[Alberto Massari]

Hi Daniel,
I have looked at the testcase you submitted, and I found two things:
1) the exception you get when using cached grammars and the DGXMLScanner is 
caused by GrammarResolver::orphanGrammar; to fix it, apply this diff

diff -u -r1.29 GrammarResolver.cpp
--- GrammarResolver.cpp 29 Sep 2004 19:27:07 -0000      1.29
+++ GrammarResolver.cpp 3 Dec 2004 16:16:23 -0000
@@ -439,7 +439,8 @@
         Grammar* grammar = fGrammarPool->orphanGrammar(nameSpaceKey);
         if (grammar)
         {
-            fGrammarFromPool->removeKey(nameSpaceKey);
+            if (fGrammarFromPool->containsKey(nameSpaceKey))
+                fGrammarFromPool->removeKey(nameSpaceKey);
             return grammar;
         }
         // It failed to remove it from the grammar pool either because it
2) as for the extra resolveEntity() you see, it's by design; 
GrammarResolver now stores the DTDs using their systemID as key (instead of 
the root element name), so, when caching is on, an extra call to 
resolveEntity is done in order to be able to invoke 
InputSource::getSystemId(). At that point, if the systemId is already in 
the cache, the input source is not parsed; if it is not in the cache, a new 
reader is created (and this triggers a new resolveEntity call)
I will change this to at least avoid the second call (as we have already 
resolved the DTD).

Thanks for the testcase,
Alberto
At 16.42 03/12/2004 +1100, Daniel McLean wrote:
I've put together a demo based on one of the sample programs shipped with
Xerces.  The demo creates a Xerces GrammarPoolImpl then conducts a number
of validating XML parses using that grammar pool when caching is enabled
for the parser.  The test documents include an XML file referring to a DTD
and an XML file referring to an XML schema.  Each type of parse is done
twice in succession to observe the caching behaviour of Xerces, with a new
parser instance created for each parse.  The parses done include:
   DGXMLScanner without caching involving DTD validation
   DGXMLScanner with caching    involving DTD validation
   IGXMLScanner without caching involving DTD validation
   IGXMLScanner with caching    involving DTD validation
   SGXMLScanner without caching involving XML schema validation
   SGXMLScanner with caching    involving XML schema validation
I ran with on an Fedora Core 1 linux x86 platform using Xerces 2.6.0.
I see a number of surprising things (refer to output below):
 - parsing fails when caching is enabled whilst using the DGXMLScanner
 - when using DGXMLScanner or IGXMLScanner for DTD validation, the DTD
   appears to be re-resolved for each parse.  I haven't checked whether
   the DTD is actually being re-parsed after being resolved each time, but
   I wonder why it is being resolved each time if it is supposedly being
   cached
 - the DTD is being resolved twice on the first parse when parsing with a
   DTD and caching enabled.  This seems questionable.
I've attached a tarball containing the files for the demo, which should
work after being unpacked into the samples directory.
Regards,
Daniel
doParse dtdDGXML
parse #1
resolveEntity("", "example.dtd")
parse #2
resolveEntity("", "example.dtd")
----------------------------
doParse dtdDGXMLCaching
parse #1
resolveEntity(null, "example.dtd")
resolveEntity("", "example.dtd")
Fatal Error at (file
/home/daniel/xerces/xerces-c-src_2_6_0/samples/GrammarCache/example-dtd.xml,
line 2, char 40): An exception occurred! Type:NoSuchElementException,
Message:The key '{0}' could not be found in the hash table
parse #2
resolveEntity(null, "example.dtd")
resolveEntity("", "example.dtd")
Fatal Error at (file
/home/daniel/xerces/xerces-c-src_2_6_0/samples/GrammarCache/example-dtd.xml,
line 2, char 40): An exception occurred! Type:NoSuchElementException,
Message:The key '{0}' could not be found in the hash table
----------------------------
doParse dtdIGXML
parse #1
resolveEntity("", "example.dtd")
parse #2
resolveEntity("", "example.dtd")
----------------------------
doParse dtdIGXMLCaching
parse #1
resolveEntity("", "example.dtd")
resolveEntity("", "example.dtd")
parse #2
resolveEntity("", "example.dtd")
----------------------------
doParse xsd
parse #1
resolveEntity("", "example.xsd")
parse #2
resolveEntity("", "example.xsd")
----------------------------
doParse xsdCaching
parse #1
resolveEntity("", "example.xsd")
parse #2
----------------------------
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