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[whatwg] Structured clone algorithm on LocalStorage

From: Darin Fisher <darin@chromium.org>
Date: Wed, 23 Sep 2009 22:19:13 -0700
Message-ID: <bd8f24d20909232219s2320ce94u51b0acf7eba56965@mail.gmail.com>
On Wed, Sep 23, 2009 at 8:10 PM, Jonas Sicking <jonas at sicking.cc> wrote:

> On Wed, Sep 23, 2009 at 3:29 PM, Jeremy Orlow <jorlow at chromium.org> wrote:
> > On Wed, Sep 23, 2009 at 3:15 PM, Jonas Sicking <jonas at sicking.cc> wrote:
> >>
> >> On Wed, Sep 23, 2009 at 2:53 PM, Brett Cannon <brett at python.org> wrote:
> >> > On Wed, Sep 23, 2009 at 13:35, Jeremy Orlow <jorlow at chromium.org>
> wrote:
> >> >> What are the use cases for wanting to store data beyond strings (and
> >> >> what
> >> >> can be serialized into strings) in LocalStorage?  I can't think of
> any
> >> >> that
> >> >> outweigh the negatives:
> >> >> 1)  From previous threads, I think it's fair to say that we can all
> >> >> agreed
> >> >> that LocalStorage is a regrettable API (mainly due to its synchronous
> >> >> nature).  If so, it seems that making it more powerful and thus more
> >> >> attractive to developers is just asking for trouble.  After all, the
> >> >> more
> >> >> people use it, the more lock contention there'll be, and the more
> >> >> browser UI
> >> >> jank users will be sure to experience.  This will also be worse
> because
> >> >> it'll be easier for developers to store large objects in
> LoaclStorage.
> >> >> 2)  As far as I can tell, there's no where else in the spec where you
> >> >> have
> >> >> to serialize structured clone(able) data to disk.  Given that
> >> >> LocalStorage
> >> >> is supposed to throw an exception if any ImageData is contained and
> >> >> since
> >> >> File and FileData objects are legal, it seems as though making
> >> >> LocalStorage
> >> >> handle structured clone data has a fairly high cost to implementors.
> >> >>  Not to
> >> >> mention that disallowing ImageData in only this one case is not
> >> >> intuitive.
> >> >> I think allowing structured clone(able) data in LocalStorage is a big
> >> >> mistake.  Enough so that, if SessionStorage and LocalStorage can't
> >> >> diverge
> >> >> on this issue, it'd be worth taking the power away from
> SessionStorage.
> >> >> J
> >> >
> >> > Speaking from experience, I have been using localStorage in my PhD
> >> > thesis work w/o any real need for structured clones (I would have used
> >> > Web Database but it isn't widely used yet and I was not sure if it was
> >> > going to make the cut in the end). All it took to come close to
> >> > simulating structured clones now was to develop my own compatibility
> >> > wrapper for localStorage (http://realstorage.googlecode.com for those
> >> > who care) and add setJSONObject() and getJSONObject() methods on the
> >> > wrapper. Works w/o issue.
> >>
> >> Actually, this seems like a prime reason *to* add structured storage
> >> support. Obviously string data wasn't enough for you so you had to
> >> write extra code in order to work around that. If structured clones
> >> had been natively supported you both would have had to write less
> >> code, and the resulting algorithms would have been faster. Faster
> >> since the browser can serialize/parser to/from a binary internal
> >> format faster than to/from JSON through the JSON serializer/parser.
> >
> > Yes, but since LocalStorage is already widely deployed, authors are stuck
> > with the the structured clone-less version of LocalStorage for a very
> long
> > time.  So the only way an app can store anything that can't be JSONified
> is
> > to break backwards compatibility.
> >
> >
> >
> > On Wed, Sep 23, 2009 at 3:11 PM, Jonas Sicking <jonas at sicking.cc> wrote:
> >>
> >> On Wed, Sep 23, 2009 at 1:35 PM, Jeremy Orlow <jorlow at chromium.org>
> wrote:
> >> > What are the use cases for wanting to store data beyond strings (and
> >> > what
> >> > can be serialized into strings) in LocalStorage?  I can't think of any
> >> > that
> >> > outweigh the negatives:
> >> > 1)  From previous threads, I think it's fair to say that we can all
> >> > agreed
> >> > that LocalStorage is a regrettable API (mainly due to its synchronous
> >> > nature).  If so, it seems that making it more powerful and thus more
> >> > attractive to developers is just asking for trouble.  After all, the
> >> > more
> >> > people use it, the more lock contention there'll be, and the more
> >> > browser UI
> >> > jank users will be sure to experience.  This will also be worse
> because
> >> > it'll be easier for developers to store large objects in LoaclStorage.
> >> > 2)  As far as I can tell, there's no where else in the spec where you
> >> > have
> >> > to serialize structured clone(able) data to disk.  Given that
> >> > LocalStorage
> >> > is supposed to throw an exception if any ImageData is contained and
> >> > since
> >> > File and FileData objects are legal, it seems as though making
> >> > LocalStorage
> >> > handle structured clone data has a fairly high cost to implementors.
> >> >  Not to
> >> > mention that disallowing ImageData in only this one case is not
> >> > intuitive.
> >> > I think allowing structured clone(able) data in LocalStorage is a big
> >> > mistake.  Enough so that, if SessionStorage and LocalStorage can't
> >> > diverge
> >> > on this issue, it'd be worth taking the power away from
> SessionStorage.
> >>
> >> Despite localStorage unfortunate locking contention problem, it's
> >> become quite a popular API. It's also very successful in terms of
> >> browser deployment since it's available in at least latest versions of
> >> IE, Safari, Firefox, and Chrome. Don't know about support in Opera?
> >
> > The more popular it becomes, the more it's going to hurt UA developers,
> web
> > developers, and users.  I don't see why this is an argument for making it
> > more powerful.
>
> How will it hurt UA developers? I think we're stuck forever to
> implement the locking mechanism. Adding more datatypes to the API
> doesn't mean that we'll have to implement it more.
>


multi-core is the future.  what's the opposite of fine-grained locking?
 it's not good ;-)

the implicit locking mechanism as spec'd is super lame.  implicitly
unlocking under
mysterious-to-the-developer circumstances!  how can that be a good thing?

storage.setItem("y",
function_involving_implicit_unlocking(storage.getItem("x")));



> > In addition, this argument assumes that Microsoft (and other UAs) will
> > implement the structured clone version of LocalStorage.  Has anyone (or
> can
> > anyone) from Microsoft comment on this?
>
> Given that I've never heard microsoft commit to a webstandard, ever, I
> doubt that we'll hear anything here. Or that the lack of hearing
> anything means we can draw any conclusions.
>
> > This is not a small feature to add.  Yes, it's smaller than creating a
> new
> > storage mechanism (that everyone is willing to adopt), but I still think
> > that's what we should be looking at.  Rather than polishing a turd.
>
> I do think that localStorage is a decent API that developers will want
> to, and should, use. I think looking into adding a async accessor to
> get a storage object so that people can use an localStorage-like API
> while avoiding risks of blocking. This would also allow sharing data
> between worker threads and the main window.
>

i think the async callback to get a storage object is an improvement, but
i'm not sure that it addresses all of the problems.  for example, if a
worker
wants to read values from storage, compute, and then put a value into
storage, it would probably do all of this from the storage callback.  that
would result in holding the lock for a long time, which would lock out any
other threads, including non-worker threads.

the problem here is that localStorage is a pile of global variables.  we are
trying to give people global variables without giving them tools to
synchronize
access to them.  the claim i've heard is that developers are not savy enough
to use those tools properly.  i agree that developers tend to use tools
without
fully understanding them.  ok, but then why are we giving them global
variables?

there has to be a better answer.

-darin
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