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Re: IndexedDB: IDBOpenDBRequest sequencing

From: Joshua Bell <jsbell@chromium.org>
Date: Thu, 10 Jan 2013 13:30:02 -0800
Message-ID: <CAD649j4hSBYbxh8eqH+hcUcJeCxuYPt4EfBOiJ2wd3PK18kAww@mail.gmail.com>
To: "public-webapps@w3.org" <public-webapps@w3.org>
Pinging the group again on this topic.

(I sent this out just before the holidays so I wasn't surprised to see this
overlooked.)


On Fri, Dec 21, 2012 at 11:26 AM, Joshua Bell <jsbell@chromium.org> wrote:

> I was playing around with the following sample:
>
> <!DOCTYPE html>
> <script>
>   var dbname = 'db' + Date.now();
>   function show(m) { return function() { console.log(m); }; }
>   openRequest1 = indexedDB.open(dbname, 1);
>     openRequest1.onblocked = show("openRequest1 - blocked");
>     openRequest1.onsuccess = function() {
>       console.log("openRequest1 - success");
>
>       openRequest2 = indexedDB.open(dbname, 2);
>       openRequest2.onblocked = show("openRequest2 - blocked");
>       openRequest2.onsuccess = show("openRequest2 - success");
>
>       deleteRequest = indexedDB.deleteDatabase(dbname);
>       deleteRequest.onblocked = show("deleteRequest - blocked");
>       deleteRequest.onsuccess = show("deleteRequest - success");
>
>       openRequest3 = indexedDB.open(dbname);
>       openRequest3.onblocked = show("openRequest3 - blocked");
>       openRequest3.onsuccess = show("openRequest3 - success");
> };
> </script>
>
> In both FF17 and IE10 the output is:
>
> openRequest1 - success
> openRequest2 - blocked
>
> If you manually execute openRequest1.result.close() the output continues:
>
> openRequest2 - success
> deleteRequest - blocked
>
> Finally, if you manually execute openRequest2.result.close() the output
> concludes:
>
> deleteRequest - success
> openRequest3 - success
>
> Given the spec, I would have expected that deleteRequest's blocked event
> would be fired immediately when the script was executed rather than waiting
> until the first connection was closed. The second open() call should follow
> the steps in 4.1 "Opening a database" through 6 ("Create a new connection
> to db..."), then in step 7 jump to 4.8 "steps for running a versionchange
> transaction", resulting in a blocked event at step 3, and in step 4 waiting
> until the first connection closes. So far so good. But in 4.11 "Database
> deletion steps" I don't see anything preventing the steps from starting or
> proceeding through step 6, resulting in a blocked event.
>
> As written, I would expect this behavior:
>
> openRequest1 - success
> openRequest2 - blocked
> deleteRequest - blocked
>
> i.e. the second open creates a connection but the versionchange must wait
> so "blocked" is fired; the delete call sets the delete pending flag, but
> must also wait so "blocked" is fired. The third connection must wait since
> the delete pending flag is set, so it waits (silently) at 4.1 step 3.
>
> If you manually execute openRequest1.result.close() the second
> connection's versionchange can proceed, leading to:
>
> openRequest2 - success
>
> Finally, if you manually execute openRequest2.result.close() there are no
> more connections so the delete can proceed. Once the delete has completed
> the third open can proceed, leading to:
>
> deleteRequest - success
> openRequest3 - success
>
> I'd chalk this up to browser bugs, but the identical behavior in FF17 and
> IE10 gives me pause. One way to model this behavior would be to imply that
> only one IDBOpenDBRequest (either an open or a delete) can be running
> against a database at a time. I don't see this stated in the spec, but it's
> a reasonable model.
>
> Can implementers speak up on their interpretations of the spec? Do we need
> to clarify the spec here one way or another?
>
>
Received on Thursday, 10 January 2013 21:30:29 GMT

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