Re: Cross-page locking mechanism for indexedDB/web storage/FileHandle ?

Based on similar feedback, I've been noodling on this too. Here are my
current thoughts:

https://gist.github.com/inexorabletash/a53c6add9fbc8b9b1191

Feedback welcome - I was planning to send this around shortly anyway.

On Wed, Jul 15, 2015 at 3:07 AM, 段垚 <duanyao@ustc.edu> wrote:

> Hi all,
>
> I'm developing an web-based editor which can edit HTML documents locally
> (stored in indexedDB).
> An issue I encountered is that there is no reliable way to ensure that at
> most one editor instance (an instance is a web page) can open a document at
> the same time.
>
> * An editor instance may create a flag entry in indexedDB or localStorage
> for each opened document to indicate "this document is locked", and remove
> this flag when the document is closed. However, if the editor is closed
> forcibly, this flag won't be removed, and the document can't be opened any
> more!
>
> * An editor instance may use storage event of localStorage to ask "is this
> document has been opened by any other editor instance". If there is no
> response for a while, it can open the document. However, storage event is
> async so we are not sure about how long the editor has to wait before
> opening the document.
>
> * IndexedDB and FileHandle do have locks, but such locks can only live for
> a short time, so can't lock an object during the entire lifetime of an
> editor instance.
>
> In a native editor application, it may use file locking (
> https://en.wikipedia.org/wiki/File_locking) to achieve this purpose.
> So maybe it is valuable to add similar locking mechanism to indexedDB/web
> storage/FileHandle?
>
> I propose a locking API of web storage:
>
>   try {
>     localStorage.lock('file1.html');
>     myEditor.open('file1.html'); // open and edit the document
>   } catch (e) {
>     alert('file1.html is already opened by another editor');
>   }
>
> Storage.lock() lock an entry if it has not been locked, and throw if it
> has been locked by another page.
> The locked entry is unlocked automatically after the page holding the lock
> is unloaded. It can also be unlocked by calling Storage.unlock().
>
> What do you think?
>
> Regards,
> Duan Yao
>
>
>
>