45668 - convert global history to use Mork's row-level APIs

Status: VERIFIED FIXED

(Core :: DOM: Navigation, defect, P3)

Description

[Chris Waterson]

Global history is currently using Mork's cell-level APIs to look up values. This
is fairly expensive, because it means that each lookup causes an allocation.
Change this to use row-level APIs which do not require this overhead.

This is important because it's called from nsILinkHandler::GetLinkState(), which
is called an enormous number of times from the style system for link coloring.

Comment 1

[Chris Waterson]

Attachment: proposed fix: replace nsIMdbRow::GetCell() with AliasCellYarn()

Comment 2

[Chris Waterson]

bienvenu: could you sanity check these changes? thanks! (FWIW, this is another
5% speed boost on page layout: drops one second out of 20 from large LXR pages...)

Comment 3

[David :Bienvenu]

Looks sane to me. One comment, though. AliasCellYarn will always succeed, so
that you can't use it to tell if a column/cell really exists in a row. It
returns an empty yarn if the cell isn't in the row. I'm not sure from your code
if you care or not. The message db code did care, because it tries to default
certain values if the cell didn't exist, and that was the one thing that broke
when I converted to the newer api.

Comment 4

[Chris Waterson]

I can test yarn.mYarn_Fill to see if there was a value, right? I'll double-check 
to make sure I've tested it when I need to...

Comment 5

[David :Bienvenu]

yes, that's right. fill will be 0.

Comment 6

[Chris Waterson]

fix checked in

Comment 7

[Claudius Gayle]

code-level fix marking VERIFIED (rubber-stamp)