Hello, everyone!
I prefer Ben's idea of a thread or cron job to keep it fresh other
than overriding a service, especially now that I'm working on
something (smarter page invalidation, which is actually smarter
invalidation of some key Tapestry caches) which changes that
PageSourceImpl a bit and this override would likely break live class
reloading. I'd have the cron/thread call ComponentSource.getPage()
instead, since PageSource is an internal service and ComponentSource
isn't.
Another possibility is to introduce a configuration to tell whether
PageSource should use regular references or soft ones, defaulting to
current behavior. Or a new service to tell whether a specific page
class should use a regular reference instead of a soft one. This would
be more flexible.
On Wed, Dec 28, 2022 at 6:55 AM Ben Weidig <b...@netzgut.net> wrote:
>
> Hi Geoff,
>
> I've read through the SoftReference documentation and as far as I
> understand it the references do only get garbage-collected in case of
> memory-pressure.
> However, the behavior to keep recently used objects is only encouraged, not
> explicitly required.
>
> Looking over the source code, you mabye can replace PageSource with a
> custom implementation that uses another caching implementation.
> Something like this (untested) code maybe?
>
> package tapestry;
>
> import java.lang.ref.SoftReference;
> import java.util.Map;
>
> import org.apache.tapestry5.commons.util.CollectionFactory;
> import org.apache.tapestry5.internal.services.PageLoader;
> import org.apache.tapestry5.internal.services.PageSourceImpl;
> import org.apache.tapestry5.internal.structure.Page;
> import
> org.apache.tapestry5.services.pageload.ComponentRequestSelectorAnalyzer;
> import org.apache.tapestry5.services.pageload.ComponentResourceSelector;
>
> public class CustomPageSourceImpl extends PageSourceImpl {
>
> private PageLoader pageLoader;
> private ComponentRequestSelectorAnalyzer selectorAnalyzer;
>
> public CustomPageSourceImpl(PageLoader pageLoader,
> ComponentRequestSelectorAnalyzer selectorAnalyzer) {
> super(pageLoader, selectorAnalyzer);
> this.pageLoader = pageLoader;
> this.selectorAnalyzer = selectorAnalyzer;
>
> }
>
> private static final record CachedPageKey(String pageName,
> ComponentResourceSelector selector) {
> }
>
> private final Map<CachedPageKey, Object> pageCache =
> CollectionFactory.newConcurrentMap();
>
> public Page getPage(String canonicalPageName)
> {
> var selector = selectorAnalyzer.buildSelectorForRequest();
>
> var key = new CachedPageKey(canonicalPageName, selector);
>
> while (true)
> {
> Object cachedObject = pageCache.get(key);
>
> Page page = null;
> if (cachedObject instanceof SoftReference<?> ref) {
> page = ref == null ? null : (Page) ref.get();
> } else {
> page = (Page) cachedObject;
> }
>
> if (page != null)
> {
> return page;
> }
> // In rare race conditions, we may see the same page loaded
> multiple times across
> // different threads. The last built one will "evict" the
> others from the page cache,
> // and the earlier ones will be GCed.
>
> page = pageLoader.loadPage(canonicalPageName, selector);
>
> // TODO: Decide here if how you want to store the Page
>
> Object cacheValue = new SoftReference<Page>(page);
>
> pageCache.put(key, cacheValue);
> }
> }
> }
>
> I'm not sure what the implications are if a page is kept forever, but as a
> SoftReference isn't guaranteed to be garbage-collected, I don't see an
> immediate downside, except needing more memory.
>
> Alternatively you could trigger the page with a cron job to keep it
> "fresh", but an overriden service is the more robust solution in my opinion.
>
> Cheers
> Ben
>
> On Tue, Dec 27, 2022 at 3:24 PM JumpStart <
> geoff.callender.jumpst...@gmail.com> wrote:
>
> > Hi,
> >
> > I have one page in my production app which takes a long time to load -
> > minimum 18 seconds. Once loaded, it is very quick to request. But from time
> > to time throughout the day, when this page is requested Tapestry decides it
> > has to reload it. I presume this is because the page cache uses
> > SoftReference (PageSourceImpl.pageCache) and the page has been garbage
> > collected. For the unlucky user, they have to wait an unbearably long time.
> > Sometimes when the system is under load the request can even time out. Is
> > there a simple, reliable, safe way to prevent it being garbage collected?
> > Or have I misunderstood what’s going on?
> >
> > Cheers,
> >
> > Geoff
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: users-unsubscr...@tapestry.apache.org
> > For additional commands, e-mail: users-h...@tapestry.apache.org
> >
> >
--
Thiago
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscr...@tapestry.apache.org
For additional commands, e-mail: users-h...@tapestry.apache.org
