Reading again the contract of hashCode(), it seems this comes down to whether or not two instances of the same class (derived from byte-equivalent JAR or what have you) on different VMs are .equals(...) to one another. I haven't found any decent resources to suggest that would even theoretically be so, given it can't be tested. I'm sold on either reading the class or supporting a manual version number. Given that these values are computed only once, is it really that difficult to do the class-reading technique you describe?
--John On Tue, Sep 9, 2008 at 6:28 PM, Louis Ryan <[EMAIL PROTECTED]> wrote: > I would be a very wary of relying on VM implementation specifics like > XXXRweriter.class.hashCode(). You certainly don't want the same class > generating different coes on different instances in a cluster where the > cache is shared. Also dont use serialVersionUID as that is only intended > for > serialization compatability. Reading the class as an InputStream from the > ClassLoader and then computing a hash might work but seems more trouble > than > its worth. > > In general I think a a manually maintained version no. might actually be > your best bet. > > On Tue, Sep 9, 2008 at 5:29 PM, John Hjelmstad <[EMAIL PROTECTED]> wrote: > > > Back to this sub-thread... > > Adding a getVersion() parameter seems error prone and a little > burdensome. > > In theory the version needs to change when any modification in potential > > output for a given input is made, ie. not just optimization. That's not > > always the easiest thing to analyze and get right. Meanwhile, > invalidating > > a > > bunch of cache keys (by registering a new rewriter impl) isn't especially > > costly: if the cache is useful at all, it will be hit often, ie. > refreshed > > quickly. > > > > --John > > > > On Tue, Sep 9, 2008 at 1:50 PM, Louis Ryan <[EMAIL PROTECTED]> wrote: > > > > > The versioning should be more explicit than that I think. Maybe add a > > > getVersion function to the rewriter interface so they can manage their > > own > > > changes > > > > > > On Tue, Sep 9, 2008 at 12:39 PM, John Hjelmstad <[EMAIL PROTECTED]> > > wrote: > > > > > > > Interesting suggestion. I can include the rewriter class names and > > their > > > > class hash codes or some other such versioning construct. > > > > > > > > On Tue, Sep 9, 2008 at 12:32 PM, Ben Laurie <[EMAIL PROTECTED]> wrote: > > > > > > > > > On Tue, Sep 9, 2008 at 8:17 PM, John Hjelmstad <[EMAIL PROTECTED]> > > > wrote: > > > > > > Excellent, agreed. CLs forthcoming. > > > > > > > > > > Can you include the version numbers of the rewriters in the cache > > key? > > > > > > > > > > > > > > > > > On Tue, Sep 9, 2008 at 12:14 PM, Kevin Brown <[EMAIL PROTECTED]> > > > wrote: > > > > > > > > > > > >> #2 is the only really viable option. If we have to put caching > > logic > > > > in > > > > > 10 > > > > > >> different places we'll screw it up 9 different times :). > > > > > >> > > > > > >> On Tue, Sep 9, 2008 at 12:11 PM, John Hjelmstad < > [EMAIL PROTECTED] > > > > > > > > wrote: > > > > > >> > > > > > >> > As discussed on a few threads and tracked in JIRA issue ( > > > > > >> > http://issues.apache.org/jira/browse/SHINDIG-579), we need to > > > move > > > > > >> > rewriting > > > > > >> > logic out of AbstractHttpCache. Yet we should maintain > rewritten > > > > > content > > > > > >> > caching capability. The question is where to put it. > > > > > >> > I see two options, at a high level: > > > > > >> > 1. In code that calls > > > > > >> ContentRewriterRegistry.rewrite(HttpResponse|Gadget). > > > > > >> > Eg. MakeRequestHandler, ProxyHandler, ViewContentFetcher, > > > > > GadgetServer, > > > > > >> and > > > > > >> > the near-future Renderer and Preloader. This allows > > finer-grained > > > > > control > > > > > >> > over caching behavior in context, at the cost of distributing > > > > caching > > > > > >> logic > > > > > >> > in various places. > > > > > >> > 2. In ContentRewriterRegistry.rewrite(HttpResponse|Gadget) > > itself, > > > > if > > > > > so > > > > > >> > chosen. Caching logic can be consolidated in > > > > > >> > CachingContentRewriterRegistry, > > > > > >> > for instance (which will no longer subclass > > > > > CachingWebRetrievalFactory), > > > > > >> > and > > > > > >> > be considered an optimization to rewriting. > > > > > >> > > > > > > >> > I'm inclined to go #2. Rewriters themselves can be augmented > > with > > > > > caching > > > > > >> > hints if necessary, and be assumed deterministic for a given > > cache > > > > key > > > > > in > > > > > >> > the meantime. Consolidating rewriting logic makes it easier to > > > share > > > > > the > > > > > >> > cache itself. > > > > > >> > > > > > > >> > Still, I might be missing situations in which additional > context > > > > > inherent > > > > > >> > to > > > > > >> > the calling context is needed to make a caching decision. > > > > > >> > > > > > > >> > --John > > > > > >> > > > > > > >> > > > > > > > > > > > > > > > > > > > > >
