1059056 - Instantiate nsDOMAttributeMap::mAttributeCache lazily

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

[Nicholas Nethercote [inactive]]

With Gmail, cnn.com and TechCrunch open, I have 1507 instances of
nsDOMAttributeMap::mAttributeCache. 1504 of them are empty, and 3 of them have
1 element. On 64-bit, at 256 bytes a pop, their combined entry storage
accounts for 385,792 bytes.

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: Instantiate nsDOMAttributeMap::mAttributeCache lazily

Comment 2

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 8479566 [details] [diff] [review]
Instantiate nsDOMAttributeMap::mAttributeCache lazily

This works, though we could also do a Maybe<AttrCache>, right?  I guess that would still be bigger than a single pointer....

r=me

Comment 3

[Andrew McCreight [:mccr8]]

Just out of idle curiosity, about what % of the empty hash tables you were seeing was this responsible for, Nick?

Comment 4

[Nicholas Nethercote [inactive]]

> Just out of idle curiosity, about what % of the empty hash tables you were
> seeing was this responsible for, Nick?

About 50%.

Comment 5

[Andrew McCreight [:mccr8]]

Nice find!

Comment 6

[Jeff Walden [:Waldo]]

Why isn't this using mozilla::UniquePtr instead of nsAutoPtr?

Comment 7

[Nicholas Nethercote [inactive]]

> Why isn't this using mozilla::UniquePtr instead of nsAutoPtr?

I just wanted to give you a chance to ask "Why isn't this using mozilla::UniquePtr instead of nsAutoPtr?"

Comment 8

[Olli Pettay [:smaug][[e-mail]]]

And I could ask why should it use mozilla::UniquePtr.

Comment 9

[Nicholas Nethercote [inactive]]

Try looks good: https://tbpl.mozilla.org/?tree=Try&rev=2e7a6d923050

Comment 10

[Jeff Walden [:Waldo]]

(In reply to Olli Pettay [:smaug] from comment #8)
> And I could ask why should it use mozilla::UniquePtr.

Because nsAutoPtr is broken in the same ways std::auto_ptr is broken, in that it can sort-of be copied, and UniquePtr implements correct lack-of-copying semantics and proper move semantics.  And also nsAutoPtr is non-standard, whereas UniquePtr emulates the standard std::unique_ptr interface, making it better for approachability/readability/understandability.

Comment 11

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/0fe77d7b34fb

Comment 12

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/0fe77d7b34fb