On Mon, 20 Aug 2001 12:27:53 -0400, "Vadim Gritsenko" <[EMAIL PROTECTED]>
wrote:
> According to http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-toolbox.html
> this technique does not work, especially on SMP systems.
Very good article, thanks for posting a reference to it!
Greetings,
Ovidiu
> Vadim
>
> > -----Original Message-----
> > From: Michael McKibben [mailto:[EMAIL PROTECTED]]
> > Sent: Monday, August 20, 2001 12:20 PM
> > To: '[EMAIL PROTECTED]'
> > Subject: RE: [C2] sitemap creation threading issue ?
> >
> >
> > I briefly glanced at the patch and one thing you can do to optimize the
> > syncronization is to apply the "double check" lock pattern. This will allow
> > you to remove the synchronized keyword from the method. For example:
> >
> > Handler sitemapHandler = (Handler)sitemaps.get(source);
> > if (sitemapHandler != null) {
> > ...
> > }
> >
> > Remove synchronized from the method and change body to:
> >
> > Handler sitemapHandler = (Handler)sitemaps.get(source);
> > if (sitemapHandler == null) {
> > synchronized (sitemaps) {
> > sitemapHandler = (Handler)sitemaps.get(source);
> > if (sitemapHandler == null) {
> > // create handler, put in the Map ...
> > sitemaps.put(...)
> > }
> > }
> > }
> >
> > Notice that threads only get synchronized in the case where a new handler
> > has not yet been created, not every call into the method!
> >
> > Regards,
> >
> > --mike
> >
> > -----Original Message-----
> > From: Morrison, John [mailto:[EMAIL PROTECTED]]
> > Sent: Monday, August 20, 2001 5:47 AM
> > To: '[EMAIL PROTECTED]'
> > Subject: RE: [C2] sitemap creation threading issue ?
> >
> >
> > Hi all, esp Marcus,
> >
> > I too have been running Load tests, I also noticed that 'something' was
> > happening regularly to slow the response. I hadn't gotten round to checking
> > the code though (the testing machines are isolated - 0 access from/to my dev
> > station).
> >
> > I saw your patch and rejoiced ;) but it's taken the response of some of my
> > pages from a couple of hundred milliseconds to over 5! I've not yet looked
> > at _what_ your patch did, but have you seen a similar increase in time?
> >
> > J.
> >
> > > -----Original Message-----
> > > From: Carsten Ziegeler [mailto:[EMAIL PROTECTED]]
> > > Sent: Monday, 20 August 2001 7:57 am
> > > To: [EMAIL PROTECTED]
> > > Subject: AW: [C2] sitemap creation threading issue ?
> > >
> > >
> > > Hi Marcus,
> > >
> > > thanks for your patch. I applied it, please cross check :-)
> > >
> > > Carsten
> > >
> > > > -----Ursprungliche Nachricht-----
> > > > Von: Marcus Crafter [mailto:[EMAIL PROTECTED]]
> > > > Gesendet: Samstag, 18. August 2001 22:41
> > > > An: Cocoon Developers Mailing List
> > > > Betreff: [C2] sitemap creation threading issue ?
> > > >
> > > >
> > > > Hi *,
> > > >
> > > > Hope all is well.
> > > >
> > > > Michael and I have spent the day testing our C2 application with
> > > > LoadRunner and have potentially uncovered a threading
> > > problem during
> > > > sitemap creation.
> > > >
> > > > We're not experts with the code but from our understanding the
> > > > following is happening, please let us know if we are
> > > right/wrong:
> > > >
> > > > There seems to be a problem with the getHandler()
> > > method, located in
> > > > the sitemap Manager class (line 154). getHandler() attempts
> > > > to access a
> > > > sitemap handler object for each request for processing. If
> > > > the handler
> > > > object is not available it creates one, causing the
> > > sitemap to be
> > > > generated.
> > > >
> > > > We've noticed under load, that many handler objects are
> > > created for
> > > > the same sitemap. This is because getHandler() does not
> > > protect the
> > > > following lines:
> > > >
> > > > Handler sitemapHandler = (Handler)sitemaps.get(source);
> > > >
> > > > and
> > > >
> > > > sitemaps.put(source, sitemapHandler);
> > > >
> > > > as a critical area.
> > > >
> > > > If multiple concurrent threads pass through
> > > getHandler() which are
> > > > requests for resources from the same sitemap, the first line
> > > > above will return null multiple times causing the same
> > > sitemap to be
> > > > compiled several times, each by individual Handler objects.
> > > >
> > > > This happens because sitemaps.put() executes after each
> > > > sitemap handler
> > > > object is created (which can take time for large sitemaps),
> > > > and cannot
> > > > prevent other incoming threads from waiting until it
> > > adds the newly
> > > > created handler object into the 'sitemaps' hashmap.
> > > >
> > > > When we synchronized the getHandler method to protect the
> > > > getting/setting of the sitemaps hashmap, we saw that the sitemap
> > > > handler object was created only once, and that the application
> > > > performed much better under load. Previously the same
> > > > sitemap handler
> > > > object was created as many times as we had simultaneous threads
> > > > make requests.
> > > >
> > > > Attached is a diff of the change we made. There might
> > > be a better
> > > > solution as the Handler class seems to be built to
> > > handle this, it's
> > > > just that the allocation of a new Handler objects per
> > > > sitemap, defeats
> > > > it's internal multi-thread logic.
> > > >
> > > > Any comments/thoughts/suggestions ?
> > > >
> > > > Cheers,
> > > >
> > > > Marcus
> > > >
> > > > --
> > > > .....
> > > > ,,$$$$$$$$$, Marcus Crafter
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