[whatwg] RFC: Alternatives to storage mutex for cookies and localStorage

[Jeremy Orlow]

On Wed, Sep 9, 2009 at 9:54 AM, Maciej Stachowiak <mjs at apple.com> wrote:

>
> On Sep 8, 2009, at 4:10 PM, Jonas Sicking wrote:
>
>  On Tue, Sep 8, 2009 at 4:00 PM, Maciej Stachowiak<mjs at apple.com> wrote:
>>
>>>
>>> On Sep 8, 2009, at 1:35 AM, Jonas Sicking wrote:
>>>
>>>
>>>> I think Firefox would be willing to break compat. The question is if
>>>> microsoft is. Which we need to ask them.
>>>>
>>>
>>> We would be very hesitant to break LocalStorage API compatibility for
>>> Safari, at least without some demonstration that the level of  real-world
>>> breakage is low (including for mobile-specific/iPhone-specific sites).
>>>
>>
>> Even if that means that you'll for all future will need to use a
>> per-domain mutex protecting localStorage? And even possibly a global
>> mutex as currently specified?
>>
>
> I don't think telling this story to users or developers will make them
> satisfied with the breakage, so the "even if" is not very relevant.
>
> I think there are ways to solve the problem without completely breaking
> compatibility. For example:
>
> - Keep the current LocalStorage API, but make it give no concurrency
> guarantees whatsoever (only single key/value accesses are guaranteed
> atomic).
> - Add a simple optional transactional model for aware authors who want
> better consistency guarantees.
>
> This might not meaningfully break existing content, unlike proposals for
> effectively mandatory new API calls. Particularly since IE doesn't have any
> kind of storage mutex.
>
> Yet another possibility is to keep a per-domain mutex, also offer a
> transactional API, and accept that careless authors may indefinitely lock up
> the UI for all pages in their domain (up to the slow script execution limit)
> if they code poorly, but in exchange won't have unexpected race conditions
> with themselves.
>

I'll see if I can't get any numbers on how widely used localStorage is
today.  Assuming that we can't break compat (which I think is a strong
possibility) I think Maciej's idea is the best one so far.  That said, I
think Chris's |window.localStorage == undefined| could work.  Both would be
confusing to web developers in different ways, but I don't think that's
avoidable (unless we break compat).
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