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

[Aaron Boodman]

On Tue, Sep 8, 2009 at 12:54 AM, Jonas Sicking<jonas at sicking.cc> wrote:
> On Tue, Sep 8, 2009 at 12:00 AM, Aaron Boodman<aa at google.com> wrote:
>> On Fri, Sep 4, 2009 at 12:02 AM, Chris Jones<cjones at mozilla.com> wrote:
>>> I propose adding the functions
>>>
>>>  window.localStorage.beginTransaction()
>>>  window.localStorage.commitTransaction()
>>> or
>>>  window.beginTransaction()
>>>  window.commitTransaction()
>>
>> I think this is a good idea! I would modify it to follow the pattern
>> set by the current SQLDatabase proposal, to have a callback, like
>> this:
>>
>> window.localStorage.transaction(function() {
>>  // use local storage here
>> });
>
> We have discussed similar APIs in the past. Something like a:
>
> window.getLocalStorage(function (storage) {
>  ...use storage...
> });
>
> This is nice because it can be expanded to something like:
> window.getSharedItems(window.SHARED_ITEM_LOCALSTORAGE |
> window.SHARED_ITEM_COOKIES, function (...) { ... });
>
> to let you access both cookies and localStorage safely at the same time.

I think worrying about safely accessing cookies is a bit of
over-design. As has been pointed out, cookies don't work correctly
today and the wheels haven't fallen off yet.

I think a solution for localStorage that doesn't fix cookies is fine.

> However, this requires breaking compatibility with existing syntax,
> something that seems impossible at this point given that Microsoft has
> shipped localStorage. I know Hixie has asked them in the past about
> how they plan to deal with the mutex problem, but I'm not sure if an
> answer has been received as of yet.

I addressed this at the end of my last message. Specifically, I suggest:

interface LocalStorageTransactionCallback {
  void handleEvent();  // note: no arguments!
};

interface LocalStorage {
  ...
  // LocalStorage can only be accessed inside this callback. Access outside
  // of it will raise an exception, except in some browsers that support such
  // behavior for legacy reasons.
  void transaction(LocalStorageTransactionCallback callback);
  ...
};

With this, there is no need to change anything about the current API.
The only change is the addition of the new transaction() method.

- a