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Date: Thu, 29 Jun 2000 14:30:26 -0700
From: Kevin Regan <kevinr@valicert.com>
Subject: RE: Performance and thread safety in Xerces
To: general@xml.apache.org
Message-id: <27FF4FAEA8CDD211B97E00902745CBE2015B7F32@seine.valicert.com>
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I don't see any problem with requiring a separate parser per thread
as long as those parsers do not somehow interact with each other
behind the scenes in a way that can not be synchronized by the user...

Sincerely,
Kevin Regan

kevinr@valicert.com

-----Original Message-----
From: Mike Pogue [mailto:mpogue@apache.org]
Sent: Thursday, June 29, 2000 2:38 PM
To: general@xml.apache.org
Subject: Re: Performance and thread safety in Xerces


Hmmmm.  The section on thread safety seems to have disappeared from the
Xerces-J docs.
There is a section in Xerces-C, however: 
http://xml.apache.org/xerces-c/faq-parse.html#faq-5

The bottom line:

	1) Making the parser 100% thread safe would be a HUGE, GIGANTIC
performance hit.
		(Did I say LARGE, BIG, MAJOR performance hit?  That,
too.)
	2) Your application knows best what needs to be locked, and what
doesn't.
	3) Therefore, although you can run the parser, DOM, etc. from
separate threads,
		we do NOT lock every method call on the parser, and each
application
		is responsible for doing appropriate locking.

Mike

Dennis Thrysoe - Netnord A/S wrote:
> 
> > Dennis Thrysoe - Netnord A/S wrote:
> > > I my concrete case I have some code that calls
> > ElementImpl.getAttribute()
> > > about 320,000 times. This code takes a bit long, and creates a
total of
> > > almost 600,000 objects.
> >
> > I would imagine that your 600,000 objects come from the fact that
> > the getAttribute method has to concatenate the children of the
> > attribute node in order to return you a string. So save the
> > memory you should use getAttributeNode and then query the
> > children yourself.
> 
> Using AttrImpl.getValue() has the same effect: Creating many objects.
Which
> otrher way is there to query the attributes value?
> 
> > > The other thing relates to the thread safety of Xerces. I have
> > two seperate
> > > threads parsing two different XML files. Still I seem to get
> > race conditions
> > > on some arrays:
> >
> > Access to the parser and the DOM are *not* thread-safe. You still
> > have to manage locks in order to ensure that multiple threads are
> >
> >   1) not using the parser at the same time
> >   2) not editing a DOM document at the same time
> >
> > Now, if there are static members that are used in the code and
> > access to them is not synchronized, then that could be causing
> > the race condition problems that you are seeing. Let us know if
> > you deduce the cause of your problem.
> 
> Does plans exist for making the parser thread safe? In our project it
is
> quite important that several threads can each parse something
different, or
> the whole idea of concurrency is wasted.
> 
> -dennis
> 
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