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List:       xerces-j-dev
Subject:    Re: Caching grammars
From:       Michael Glavassevich <mrglavas () ca ! ibm ! com>
Date:       2013-01-20 20:05:22
Message-ID: OFDF1F0A76.1B0F6834-ON85257AF9.006D5F93-85257AF9.006E59AC () ca ! ibm ! com
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Xerces' grammar objects are thread-safe. The ones cached in the JAXP 
Schema object are shared with each Validator created from the JAXP Schema.

Thanks.

Michael Glavassevich
XML Technologies and WAS Development
IBM Toronto Lab
E-mail: mrglavas@ca.ibm.com
E-mail: mrglavas@apache.org

Robert Huffman <robert.huffman@gmail.com> wrote on 20/01/2013 01:59:33 PM:

> That does seem to be the way it works. I dug into the source more 
> after my initial post. It seems that the grammar pool in the Schema 
> is used to initialize a second grammar pool owned by the Validator. 
> This second grammar pool lives only as long as the validator.
> 
> I haven't gotten back into that part of my code in a week or so, but
> I believe I can ultimately get my grammars that are dynamically 
> loaded via the LSResourceResolver by reusing my Validator. Of 
> course, the Validator is not thread-safe, so I will probably use a 
> ThreadLocal<Validator>. (Synchronizing a single validator is 
> probably not acceptable in my environment.)
> 
> Of course, that means I will end up with a grammar cache in each 
> thread in my thread pool. So my next step is to figure out if the 
> grammars are thread safe. If they are, perhaps I can figure out a 
> way to share a single instance of a thread safe grammar cache 
> between validators.
> 
> On Sun, Jan 20, 2013 at 10:23 AM, Michael Glavassevich 
<mrglavas@ca.ibm.com
> > wrote:
> The JAXP Schema created through SchemaFactory.newSchema() caches 
grammars
> (through SoftReferences [1]) by their schema location. It's been quite
> awhile since I've looked at how this works, but it wouldn't surprise me 
if
> Xerces calls your LSResourceResolver each time you validate in order to
> give your application an opportunity to redirect the schema location and
> then use the value returned from the LSResourceResolver to look up the
> cached grammar.
> 
> Thanks.
> 
> [1]
> http://svn.apache.org/viewvc/xerces/java/trunk/src/org/apache/
> xerces/jaxp/validation/SoftReferenceGrammarPool.java?annotate=699892
> 
> Michael Glavassevich
> XML Technologies and WAS Development
> IBM Toronto Lab
> E-mail: mrglavas@ca.ibm.com
> E-mail: mrglavas@apache.org
> 
> Robert Huffman <robert.huffman@gmail.com> wrote on 12/01/2013 05:04:17 
PM:
> 
> > I must parse documents that may use a large number of fairly large
> > XSDs. However, the large majority of documents will not use most of
> > those XSDs. Therefore, I would like to use a custom
> > LSResourceResolver to resolve the target namespaces to local
> > resources during parsing rather than building a Schema object that
> > has all the grammars loaded up front.
> >
> > Unfortunately, as nearly as I can tell, grammars loaded through the
> > use of a LSResourceResolver are never cached in the grammar pool. Is
> > that correct? Is there some nuance I'm missing?
> 

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