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Re: IndexedDB: IDBOpenDBRequest sequencing

From: Joshua Bell <jsbell@chromium.org>
Date: Tue, 26 Feb 2013 17:19:58 -0800
Message-ID: <CAD649j5stj3dd7qOaUaGPbtz7jv0r6iWrAE8QSk7hoSNPrne2w@mail.gmail.com>
To: Jonas Sicking <jonas@sicking.cc>
Cc: "public-webapps@w3.org" <public-webapps@w3.org>
On Tue, Feb 26, 2013 at 5:02 PM, Jonas Sicking <jonas@sicking.cc> wrote:

> 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;
>
> Agreed so far.
>
> > 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.
>
> I agree that this is what the spec says, but this seems like a spec
> bug to me. I'd prefer is the "blocked" event was always fired if the
> "success" event is hindered due to someone keeping the database open.
> I.e. we should only wait silently there if all open connections to the
> database (if any) have the closePending flag set.
>
>
Agreed in principal - waiting silently doesn't seem helpful. Will need to
ponder how to reflect this in the spec, though.


> > 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?
>
> The current Firefox behavior definitely seems like a bug to me.
>
> I think that the proper set of events is either
>
> openRequest1 - success
> openRequest2 - blocked
> deleteRequest - blocked
> openRequest3 - blocked
>
> or
>
> openRequest2 - success
> deleteRequest - blocked
> openRequest3 - blocked
> openRequest1 - error
>
> Note that the spec already says that if two requests to open the same
> database, but with different versions, happens "at the same time" then
> the one with the higher version number is attempted to be opened first
> and if that's successful the one with the lower numbers receives an
> error.
>
> See the Notes in 4.1 step 3.
>
> "at the same time" is of course hard to define.
>

In my sample, openRequest2/deleteRequest/openRequest3 are made in the
"success" handler of openRequest1, so I'm not sure how the openRequest1
could fail.

Agreed that "at the same time" leaves wiggle room for 2 vs. 3, though. 3
also opens with the "current version" which require definition when other
requests are in the process of upgrading the database. I think I suggested
text for that in one of the open bugs.



>
> / Jonas
>
Received on Wednesday, 27 February 2013 01:20:26 GMT

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