68885 - nsXBLService::StripWhitespaceNodes() is expensive

Status: VERIFIED INVALID

(Core :: XBL, defect)

Description

[rbs]

In order to avoid ignorable whitespace, XBL uses StripWhitespaceNodes() to walk
the content model, removing each content which is only whitespace:
        aElement->RemoveChildAt(i, PR_TRUE);

This is a very expensive operation because for each call, observers
of the document are notified, among which is the famous frame construction
code, which grovels through the equally famous GetPrimaryFrameFor() ...

I can see this by putting a beak point before the call, and then entering
in that call.

Since whitespace nodes are usually before and after a tag, \n<tag>...</tag>\n,
the overall cost of these removals can be huge. Maybe a leaner solution
is possible -- such as not notifying?

There is a related discussion on ignorable whitespace going on in bug 68411.

Comment 1

[David Hyatt]

I have no idea why I made this notification noisy.  Making it non-noisy works
just fine.

Comment 2

[David Hyatt]

XBL docs are loaded without a presshell, which means the front end code is not
notified, so whether or not this notification is noisy or not is irrelevant.

Comment 3

[David Hyatt]

Marking INVALID.  Reopen if you have reproducible evidence that the front end
code is being called.  My tests show it is not.

Comment 4

[Chad Austin]

invalids, wontfixes, dups, worksformes