[Engine-devel] Dynamic resource loading in GWT

Einav Cohen ecohen at redhat.com
Thu Aug 8 13:16:00 UTC 2013 

> ----- Original Message -----
> From: "Roy Golan" <rgolan at redhat.com>
> Sent: Thursday, August 8, 2013 5:14:57 AM
> 
> On 08/07/2013 04:50 PM, Einav Cohen wrote:
> > [top posting]
> >
> > in general, gwt applications are not "built" for loading things at
> > run-time.
> > for the branding feature, we had to change some of that due to the feature
> > requirements.
> >
> > question is what will we gain from loading dynamically the values that are
> > currently being loaded statically.
> > for features such as dynamic/user-defined OSs [1] - it makes sense and
> > probably
> > even required, however, for error messages, which are not
> > dynamic/user-defined,
> > I think that it doesn't.
> 
> error messages changes when the engine changes them. the fact that there
> is 1 source and 3 copies is a mess
> so the point is not about making the error message "dynamic" - its about
> loading them always from the same source
> i.e - instead of error.js created by GWT(or whatever its hiding in) load
> it from [server]/fileServlet?f=errors
> 
> also its not only about error messages.
> Virt team want to load the system timezones. today its done via Query -
> Query should be used to get Entities no sources
> I'm sure lots of things are limited/complicate impl/buggy by the lack
> easy way of resource sharing.
> 
> we can start with a POC which will be used to load Timezones what do say?

in general, loading dynamically (in run time) data that is already "known" in 
compilation time doesn't make much sense to me.
having said that, after giving it some more thought: I agree with you, and the 
reason for that is that there is a chance that "tomorrow", the GUI and the 
engine-core might be separated to different projects/repos/etc., so sharing 
resources between them during compilation time might be very challenging.

so I think that you can definitely start with a POC of timezone loading, however 
we (GUI maintainers) must give some serious thought on resource sharing in general 
(in case we will indeed move towards separating the GUI from the core), given the 
fact that the gwt infrastructure / concept contradicts dynamic loading, in a sense.

> 
> 
> > there are other ways to ease maintenance of error-messages (e.g. maintain
> > only
> > one copy of each file, and copy it during compilation time to the relevant
> > locations, instead of maintaining several identical files), without
> > introducing
> > the disadvantages of dynamic loading.
> >
> > ----
> > Thanks,
> > Einav
> >
> > [1] http://www.ovirt.org/OS_info
> >
> > ----- Original Message -----
> >> From: "Roy Golan" <rgolan at redhat.com>
> >> To: awels at redhat.com
> >> Cc: engine-devel at ovirt.org
> >> Sent: Wednesday, August 7, 2013 9:35:30 AM
> >> Subject: Re: [Engine-devel] Dynamic resource loading in GWT
> >>
> >> On Wed 07 Aug 2013 03:23:36 PM IDT, Alexander Wels wrote:
> >>> On Wednesday, August 07, 2013 02:48:45 PM Roy Golan wrote:
> >>>> On 08/07/2013 02:08 PM, Einav Cohen wrote:
> >>>>> Hi Roy,
> >>>>>
> >>>>> a couple of notes (I could be totally wrong here, GWT experts - please
> >>>>> review/comment):
> >>>>>
> >>>>> - from [1]:
> >>>>> "Provides dynamic string lookup of key/value string pairs defined in a
> >>>>> module's host HTML page" - there is a chance that a gwt dictionary is
> >>>>> limited to reading key/value string pairs that reside within the *gwt
> >>>>> module host HTML page* (i.e., within the context of the GWT application
> >>>>> -
> >>>>> "http://[server]/webadmin/webadmin/...") and not outside - need to find
> >>>>> that out.
> >>>> well the file servlet resides on [server] so I don't think there a "same
> >>>> origin policy" problem here - correct me if I'm wrong (isn't branding
> >>>> doing something similar?)
> >>>>
> >>> Branding is doing exactly what you are suggesting, generating a
> >>> dictionary
> >>> in
> >>> the host page, and having the GWT application read it at runtime. The
> >>> only
> >>> reason we did it like that, is that there is no other way of changing
> >>> some
> >>> of
> >>> the messages at runtime. If there was some way of doing it at compile
> >>> time
> >>> I
> >>> would have done that. Also the number of resources changed by branding is
> >>> very
> >>> limited and therefore won't impact the performance as much as doing every
> >>> single resource.
> >>>
> >>> There are advantages and disadvantages of both methods that need to be
> >>> carefully weighed, and the GWT developers themselves did that and came to
> >>> the
> >>> conclusion that compile time inclusion is the best method for most
> >>> resources.
> >>> They did however anticipate the need for some runtime resources so they
> >>> included Dictionary etc.
> >>>
> >>>>> - again, from [1]:
> >>>>> "a variety of error conditions (particularly those involving key
> >>>>> mismatches) cannot be caught until runtime. Similarly, the GWT compiler
> >>>>> is unable discard unused dictionary values since the structure cannot
> >>>>> be
> >>>>> statically analyzed".
> >>>>> (this is expected, as the suggested loading here is dynamic, rather
> >>>>> than
> >>>>> static)
> >>>>>
> >>>>> - not sure exactly how this would work with localization; there is "A
> >>>>> Caveat Regarding Locale" mentioned in [1] - IIUC, we will lose the
> >>>>> automatic locale-mapping that we have today, and we would need to do it
> >>>>> ourselves somehow (not a big deal, I suppose, just some extra work that
> >>>>> needs to be done here).
> >>> The branding allows one to define java property bundles for all the
> >>> supported
> >>> languages, and will load them at runtime and put the translated strings
> >>> in
> >>> the
> >>> Dictionary in the host page. Again I wouldn't recommend doing it for a
> >>> large
> >>> number of resources.
> >> why?
> >> and what number is large?
> >>>> indeed but it will pay off. a change off resources means ctrl+F5 and not
> >>>> GWT compilation :P
> >>>>
> >>> Sure for the developer it would be great, less compiling. However for the
> >>> user
> >>> not so much,
> >> isn't admin is gaining from it? and development time and bugs around
> >> messages?
> >>
> >>   and in the end we are creating the software for the user and the
> >>> needs of the developer are secondary to that. When I say it is not so
> >>> great
> >>> for the user, I mean the fact that it becomes a lot harder to cache the
> >>> host
> >>> page (as the contents can change), vs caching the compiled resources is
> >>> really
> >>> easy as the contents won't chance.
> >> in the end both are cached so there is no memory overhead.
> >>>
> >>>>> ----
> >>>>> Thanks,
> >>>>> Einav
> >>>>>
> >>>>> [1]
> >>>>> http://www.gwtproject.org/javadoc/latest/com/google/gwt/i18n/client/Dicti
> >>>>> onary.html
> >>>>>
> >>>>> ----- Original Message -----
> >>>>>
> >>>>>> From: "Roy Golan" <rgolan at redhat.com>
> >>>>>> To: "engine-devel" <engine-devel at ovirt.org>
> >>>>>> Sent: Wednesday, August 7, 2013 2:59:07 AM
> >>>>>> Subject: [Engine-devel] Dynamic resource loading in GWT
> >>>>>>
> >>>>>> Painful issue here - we all know the regular drill of maintaining
> >>>>>> messages in many places, I18N files and so on.
> >>>>>> Also there's a patch to make all available timezone an java enum and
> >>>>>> by
> >>>>>> that share it for free with the UI. its a way better than a backend
> >>>>>> Query.
> >>>>>>
> >>>>>> But this is all hard-coded, not flexible, hard to maintain, we all
> >>>>>> know.
> >>>>>>
> >>>>>> Why won't we make GWT load a javascript dictionary/dictionaries from a
> >>>>>> servlet or our host page html[1] using GWT Dictionary[3]?
> >>>>>>
> >>>>>> that way the configuration is shared with the engine, it relies on the
> >>>>>> disk, customers and GSS can change it on-site and so on.
> >>>>>>
> >>>>>> | index.html | -> | file servlet | -> |read
> >>>>>> | /etc/ovirt-engine/conf/...|
> >>>>>> |
> >>>>>>         ^
> >>>>>> |
> >>>>>> | GWT loads Dictionary |
> >>>>>>
> >>>>>> candidates for dynamic resources
> >>>>>> * I18N resources AppErrors...
> >>>>>> * config ( just the UI subset )
> >>>>>> * osinfo ?
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> [1] host page html -
> >>>>>> http://www.gwtproject.org/doc/latest/DevGuideOrganizingProjects.html#DevG
> >>>>>> uideHostPage [2] Dynamic string internationalisation -
> >>>>>> http://www.gwtproject.org/doc/latest/DevGuideI18n.html#DevGuideDynamicStr
> >>>>>> ingInternationalization [3]
> >>>>>> http://www.gwtproject.org/javadoc/latest/com/google/gwt/i18n/client/Dicti
> >>>>>> onary.html
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Roy
> >>>>>> _______________________________________________
> >>>>>> Engine-devel mailing list
> >>>>>> Engine-devel at ovirt.org
> >>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
> >>>> _______________________________________________
> >>>> Engine-devel mailing list
> >>>> Engine-devel at ovirt.org
> >>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
> >>
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> >>
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