<div class="gmail_quote">On Thu, Sep 24, 2009 at 1:17 AM, Darin Fisher <span dir="ltr"><<a href="mailto:darin@chromium.org">darin@chromium.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="gmail_quote"><div><div></div><div class="h5">On Thu, Sep 24, 2009 at 12:20 AM, Jonas Sicking <span dir="ltr"><jonas@sicking.cc></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div></div><div>On Wed, Sep 23, 2009 at 10:19 PM, Darin Fisher <<a href="mailto:darin@chromium.org" target="_blank">darin@chromium.org</a>> wrote:<br>
><br>
><br>
> On Wed, Sep 23, 2009 at 8:10 PM, Jonas Sicking <jonas@sicking.cc> wrote:<br>
>><br>
>> On Wed, Sep 23, 2009 at 3:29 PM, Jeremy Orlow <<a href="mailto:jorlow@chromium.org" target="_blank">jorlow@chromium.org</a>> wrote:<br>
>> > On Wed, Sep 23, 2009 at 3:15 PM, Jonas Sicking <jonas@sicking.cc> wrote:<br>
>> >><br>
>> >> On Wed, Sep 23, 2009 at 2:53 PM, Brett Cannon <<a href="mailto:brett@python.org" target="_blank">brett@python.org</a>> wrote:<br>
>> >> > On Wed, Sep 23, 2009 at 13:35, Jeremy Orlow <<a href="mailto:jorlow@chromium.org" target="_blank">jorlow@chromium.org</a>><br>
>> >> > wrote:<br>
>> >> >> What are the use cases for wanting to store data beyond strings (and<br>
>> >> >> what<br>
>> >> >> can be serialized into strings) in LocalStorage? I can't think of<br>
>> >> >> any<br>
>> >> >> that<br>
>> >> >> outweigh the negatives:<br>
>> >> >> 1) From previous threads, I think it's fair to say that we can all<br>
>> >> >> agreed<br>
>> >> >> that LocalStorage is a regrettable API (mainly due to its<br>
>> >> >> synchronous<br>
>> >> >> nature). If so, it seems that making it more powerful and thus more<br>
>> >> >> attractive to developers is just asking for trouble. After all, the<br>
>> >> >> more<br>
>> >> >> people use it, the more lock contention there'll be, and the more<br>
>> >> >> browser UI<br>
>> >> >> jank users will be sure to experience. This will also be worse<br>
>> >> >> because<br>
>> >> >> it'll be easier for developers to store large objects in<br>
>> >> >> LoaclStorage.<br>
>> >> >> 2) As far as I can tell, there's no where else in the spec where<br>
>> >> >> you<br>
>> >> >> have<br>
>> >> >> to serialize structured clone(able) data to disk. Given that<br>
>> >> >> LocalStorage<br>
>> >> >> is supposed to throw an exception if any ImageData is contained and<br>
>> >> >> since<br>
>> >> >> File and FileData objects are legal, it seems as though making<br>
>> >> >> LocalStorage<br>
>> >> >> handle structured clone data has a fairly high cost to implementors.<br>
>> >> >> Not to<br>
>> >> >> mention that disallowing ImageData in only this one case is not<br>
>> >> >> intuitive.<br>
>> >> >> I think allowing structured clone(able) data in LocalStorage is a<br>
>> >> >> big<br>
>> >> >> mistake. Enough so that, if SessionStorage and LocalStorage can't<br>
>> >> >> diverge<br>
>> >> >> on this issue, it'd be worth taking the power away from<br>
>> >> >> SessionStorage.<br>
>> >> >> J<br>
>> >> ><br>
>> >> > Speaking from experience, I have been using localStorage in my PhD<br>
>> >> > thesis work w/o any real need for structured clones (I would have<br>
>> >> > used<br>
>> >> > Web Database but it isn't widely used yet and I was not sure if it<br>
>> >> > was<br>
>> >> > going to make the cut in the end). All it took to come close to<br>
>> >> > simulating structured clones now was to develop my own compatibility<br>
>> >> > wrapper for localStorage (<a href="http://realstorage.googlecode.com" target="_blank">http://realstorage.googlecode.com</a> for those<br>
>> >> > who care) and add setJSONObject() and getJSONObject() methods on the<br>
>> >> > wrapper. Works w/o issue.<br>
>> >><br>
>> >> Actually, this seems like a prime reason *to* add structured storage<br>
>> >> support. Obviously string data wasn't enough for you so you had to<br>
>> >> write extra code in order to work around that. If structured clones<br>
>> >> had been natively supported you both would have had to write less<br>
>> >> code, and the resulting algorithms would have been faster. Faster<br>
>> >> since the browser can serialize/parser to/from a binary internal<br>
>> >> format faster than to/from JSON through the JSON serializer/parser.<br>
>> ><br>
>> > Yes, but since LocalStorage is already widely deployed, authors are<br>
>> > stuck<br>
>> > with the the structured clone-less version of LocalStorage for a very<br>
>> > long<br>
>> > time. So the only way an app can store anything that can't be JSONified<br>
>> > is<br>
>> > to break backwards compatibility.<br>
>> ><br>
>> ><br>
>> ><br>
>> > On Wed, Sep 23, 2009 at 3:11 PM, Jonas Sicking <jonas@sicking.cc> wrote:<br>
>> >><br>
>> >> On Wed, Sep 23, 2009 at 1:35 PM, Jeremy Orlow <<a href="mailto:jorlow@chromium.org" target="_blank">jorlow@chromium.org</a>><br>
>> >> wrote:<br>
>> >> > What are the use cases for wanting to store data beyond strings (and<br>
>> >> > what<br>
>> >> > can be serialized into strings) in LocalStorage? I can't think of<br>
>> >> > any<br>
>> >> > that<br>
>> >> > outweigh the negatives:<br>
>> >> > 1) From previous threads, I think it's fair to say that we can all<br>
>> >> > agreed<br>
>> >> > that LocalStorage is a regrettable API (mainly due to its synchronous<br>
>> >> > nature). If so, it seems that making it more powerful and thus more<br>
>> >> > attractive to developers is just asking for trouble. After all, the<br>
>> >> > more<br>
>> >> > people use it, the more lock contention there'll be, and the more<br>
>> >> > browser UI<br>
>> >> > jank users will be sure to experience. This will also be worse<br>
>> >> > because<br>
>> >> > it'll be easier for developers to store large objects in<br>
>> >> > LoaclStorage.<br>
>> >> > 2) As far as I can tell, there's no where else in the spec where you<br>
>> >> > have<br>
>> >> > to serialize structured clone(able) data to disk. Given that<br>
>> >> > LocalStorage<br>
>> >> > is supposed to throw an exception if any ImageData is contained and<br>
>> >> > since<br>
>> >> > File and FileData objects are legal, it seems as though making<br>
>> >> > LocalStorage<br>
>> >> > handle structured clone data has a fairly high cost to implementors.<br>
>> >> > Not to<br>
>> >> > mention that disallowing ImageData in only this one case is not<br>
>> >> > intuitive.<br>
>> >> > I think allowing structured clone(able) data in LocalStorage is a big<br>
>> >> > mistake. Enough so that, if SessionStorage and LocalStorage can't<br>
>> >> > diverge<br>
>> >> > on this issue, it'd be worth taking the power away from<br>
>> >> > SessionStorage.<br>
>> >><br>
>> >> Despite localStorage unfortunate locking contention problem, it's<br>
>> >> become quite a popular API. It's also very successful in terms of<br>
>> >> browser deployment since it's available in at least latest versions of<br>
>> >> IE, Safari, Firefox, and Chrome. Don't know about support in Opera?<br>
>> ><br>
>> > The more popular it becomes, the more it's going to hurt UA developers,<br>
>> > web<br>
>> > developers, and users. I don't see why this is an argument for making<br>
>> > it<br>
>> > more powerful.<br>
>><br>
>> How will it hurt UA developers? I think we're stuck forever to<br>
>> implement the locking mechanism. Adding more datatypes to the API<br>
>> doesn't mean that we'll have to implement it more.<br>
><br>
><br>
> multi-core is the future. what's the opposite of fine-grained locking?<br>
> it's not good ;-)<br>
> the implicit locking mechanism as spec'd is super lame. implicitly<br>
> unlocking under<br>
> mysterious-to-the-developer circumstances! how can that be a good thing?<br>
> storage.setItem("y",<br>
> function_involving_implicit_unlocking(storage.getItem("x")));<br>
<br>
</div></div>I totally agree on all points. The current API has big imperfections.<br>
However I haven't seen any workable counter proposals so far, and I<br>
honestly don't believe there are any as long as our goals are:<br>
<br>
* Don't break existing users of the current implementations.<br>
* Don't expose race conditions to the web.<br>
* Don't rely on authors getting explicit locking mechanisms right.<br>
<br></blockquote><div><br></div></div></div><div>The current API exposes race conditions to the web. The implicit</div><div>dropping of the storage lock is that. In Chrome, we'll have to drop</div><div>an existing lock whenever a new lock is acquired. That can happen</div>
<div>due to a variety of really odd cases (usually related to nested loops</div><div>or nested JS execution), which will be difficult for developers to</div><div>predict, especially if they are relying on third-party JS libraries.</div>
<div><br></div><div>This issue seems to be discounted for reasons I do not understand.</div><div><div></div><div class="h5"><div><br></div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
But, as imperfect as the current API is, I think the following is a<br>
decent way forward:<br>
<br>
* Allow pages that want the convenience of localStorage to use it. For<br>
multi-process browsers this will mean poor UI *for pages that use<br>
localStorage*. Especially when said pages hold on to localStorage for<br>
a long time.<br>
* Add alternative APIs that don't suffer from the same problems. More below.<br>
<div><div></div><div><br>
>> > In addition, this argument assumes that Microsoft (and other UAs) will<br>
>> > implement the structured clone version of LocalStorage. Has anyone (or<br>
>> > can<br>
>> > anyone) from Microsoft comment on this?<br>
>><br>
>> Given that I've never heard microsoft commit to a webstandard, ever, I<br>
>> doubt that we'll hear anything here. Or that the lack of hearing<br>
>> anything means we can draw any conclusions.<br>
>><br>
>> > This is not a small feature to add. Yes, it's smaller than creating a<br>
>> > new<br>
>> > storage mechanism (that everyone is willing to adopt), but I still think<br>
>> > that's what we should be looking at. Rather than polishing a turd.<br>
>><br>
>> I do think that localStorage is a decent API that developers will want<br>
>> to, and should, use. I think looking into adding a async accessor to<br>
>> get a storage object so that people can use an localStorage-like API<br>
>> while avoiding risks of blocking. This would also allow sharing data<br>
>> between worker threads and the main window.<br>
><br>
> i think the async callback to get a storage object is an improvement, but<br>
> i'm not sure that it addresses all of the problems. for example, if a<br>
> worker<br>
> wants to read values from storage, compute, and then put a value into<br>
> storage, it would probably do all of this from the storage callback. that<br>
> would result in holding the lock for a long time, which would lock out any<br>
> other threads, including non-worker threads.<br>
> the problem here is that localStorage is a pile of global variables. we are<br>
> trying to give people global variables without giving them tools to<br>
> synchronize<br>
> access to them. the claim i've heard is that developers are not savy enough<br>
> to use those tools properly. i agree that developers tend to use tools<br>
> without<br>
> fully understanding them. ok, but then why are we giving them global<br>
> variables?<br>
> there has to be a better answer.<br>
<br>
</div></div>I actually described an potential solution in the thread on worker storage.<br>
<br>
The problem you describe is a worker holding on the the storage for an<br>
very long (indefinite) time, thereby locking out other threads/windows<br>
from accessing the same storage area. This seems inevitable if we want<br>
to prevent race conditions while at the same time not forcing the<br>
complexities of locks onto web developers. The WebDatabase API suffers<br>
from exactly the same problem.<br></blockquote><div><br></div></div></div><div>Hmm... are you saying that from the SQLStatementCallback used to read</div><div>some data out of the database, you might compute on that data, and then</div>
<div>issue an executeSql call to write a computed result, and that in this scenario,</div><div>the fact that it is the same transaction means that other threads are locked</div><div>out of accessing the same database? I hadn't considered chaining executeSql</div>
<div>calls like this to keep the transaction alive. Hmm...</div><div><div></div><div class="h5"><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
However, we can lessen the problem. By adding multiple storage areas,<br>
we can allow a worker to use one storage area, while allowing other<br>
parties to simultaneously use other storage areas. This way, if a<br>
worker and a window aren't sharing data at all, they never get in the<br>
way of each other.<br>
<br>
So a very simplistic design would be something like the following:<br>
<br>
getStorageArea(name, callback)<br>
<br>
when called will asynchronously call the callback parameter once the<br>
storage area named by the first parameter becomes available. The<br>
callback receives the storage area as an argument. We would also have<br>
the function<br>
<br>
getMultipleStorageAreas(names, callback)<br>
<br>
Same as above, but names is an array of strings indicating multiple<br>
storage areas that need to be acquired before the callback is called.<br>
The callback receives all the areas in an array as an argument. This<br>
function allows transferring data between multiple storage areas<br>
without risking racing.<br>
<br>
There's several problems with this, such as the names are sort of<br>
crappy, and that getting storage areas an array isn't very friendly.<br>
However you get the basic idea.<br>
<br>
We don't even need to use Storage objects for this. In fact, I hope<br>
mozilla will in a not too distant future come up with an alternative<br>
proposal to the WebDatabase SQL API. Something like this might fit<br>
into such a proposal as I think that'll have multiple separate storage<br>
areas anyway.<br>
<font color="#888888"><br>
/ Jonas<br>
</font></blockquote></div></div></div><br><div><br></div><div>Maybe we should just invent a similar transaction method for name/value</div><div>storage? Wouldn't that be better than inventing a new idiom? Ideally,</div>
<div>we'd also make reads and writes on storage be asynchronous. The</div>
<div>transaction would then be usable to hold the lock across multiple</div><div>asynchronous reads and writes. Since local storage is backed by disk,</div><div>it seems like a more ideal local storage API would not require synchronous</div>
<div>filesystem access.</div><div><br></div><font color="#888888"><div>-Darin</div>
</font></blockquote></div><br><div><br></div><div>I forgot to say that I like the name proposal. It gives domains a way to</div><div>carve up their storage, avoiding the need to create dummy hostnames.</div><div><br></div>
<div>-Darin</div>