Bug 62590 – REGRESSION(r82934-r83016): Non-parallel downloads of linked stylesheets with media attribute

• Component: Page Loading
• Status: NEW

Created attachment 96996 [details]
Reduced Test Case

The WebKit nightly for Windows r82934 downloads linked stylesheets with a media attribute in parallel. The WebKit nightly for Windows r83016 does not download the linked stylesheets with media attributes in parallel.

Steps to reproduce:
1. Open the Network panel of the Web Inspector.
2. Load the linked jsbin page or the attached reduced test case.
3. Note the stylesheet resources loaded from hang.nodester.com

The hang.nodester.com server waits two seconds before sending a response. This makes it easy to see the stair-stepping pattern (on r83016 and on) indicating the browser is waiting for the previous stylesheet to download before downloading the next. In r82934, the stylesheets download in roughly the same amount of time.

I looked at the changes (http://trac.webkit.org/?from=04%2F06%2F2011&daysback=1&changeset=on&wiki=on&update=Update), and the one that looks to me like it could have changed this behavior is <http://trac.webkit.org/changeset/82951>.

Some additional test URLs:
Link with no media and one with media="print": http://jsbin.com/akumi5
Link with no media and one with media="crazy" (non-existent media type): http://jsbin.com/akumi5

Oops, the "crazy" media type test case link should be http://jsbin.com/ukidu5

[Alexey Proskuryakov]

Isn't it how it should work? Only one of these stylesheets needs to be downloaded quickly, as only one is going to be used for screen rendering. The rest can be fetched with lowest priority.

I agree that the stylesheets that will be used immediately for screen rendering should be downloaded quickly, but I don't believe the other stylesheets need to be downloaded serially.

I tested with @media="screen" (http://jsbin.com/ibofa4) and with media queries that should immediately apply (http://jsbin.com/ixemu4). In both tests, the stylesheets to be immediately used were downloaded in parallel. That's good.

However, going back to the original test case (http://jsbin.com/ajigu4 or attachment 96996 [details]) with media queries for smaller window sizes, even after the "large" stylesheet (which will be immediately used for screen rendering) has downloaded, why are the other two stylesheets downloaded serially even when they are the only remaining resources to be downloaded and the only resources to be downloaded from hang.nodester.com?

In Aurora 6.0a2(2011-06-13), Firefox 4.0.1, Opera 11.11, Opera 11.50 beta (build 1040), and WebKit prior to and including r82934, the stylesheets download in parallel, with the load event firing usually around 2 seconds. In WebKit revision 83016 and on, the load event fires around 7 seconds.

[Alexey Proskuryakov]

Yes, that sounds wrong to me. It might be just an artifact of Web Inspector network panel, which is largely broken now (see bug 53828).

Created attachment 97138 [details]
Chrome Stable Network Panel Screenshot

I don't think it's a Web Inspector artifact (specifically bug 53828), as Chrome stable (12.0.742.91) shows that the stylesheets are non being downloaded in parallel. The attached screenshot shows Chrome's Network panel after loading attachment 96996 [details]. It doesn't display the resources starting to download at the same time like bug 53828.

[Tony Gentilcore]

Looks like this bug still exists. Fixing it could be a nice page load time win for some sites.