804948 - Add an early-return for scrollbox.ensureElementIsVisible when there is no overflow

Status: RESOLVED DUPLICATE of bug 752376

(Toolkit :: UI Widgets, defect)

Description

[Jared Wein [:jaws] (please needinfo? me)]

This profile, http://people.mozilla.com/~bgirard/cleopatra/?report=dee237c64c55db4ab71691167424dd52738965c7, shows some terrible slow-down when switching tabs from about:blank to a long data URI.

There is a large amount of time spent calculating the boundingRect for the scrollbox in _handleTabSelect -> ensureElementIsVisible -> get_scrollClientRect.

I don't think this is necessary if there is no overflow in the scrollbox. I may be missing something, but I think we can assume that the element is visible if the scrollbuttons are collapsed.

This patch adds an early-return in the case that there is no overflow on the tabstrip, which removes the single most expensive part of the associated profile.

Comment 1

[Jared Wein [:jaws] (please needinfo? me)]

Attachment: Patch

See comment #0 for an explanation of this patch. I ran into issues filing this bug.

Comment 2

[Jared Wein [:jaws] (please needinfo? me)]

You can use the data URI in https://www.msu.edu/~weinjare/804948/largeDataURI.txt to test with this.

Open one tab with this data URI
Open another tab to about:blank
Wait > 10 seconds for the image to be discarded
Now switch back to the image tab