Bug 145817 – GraphicsContext state stack wasting lots of memory when empty.

• Status: RESOLVED
• Resolution: FIXED
• Component: Canvas

[Andreas Kling]

GraphicsContext::restore() uses removeLast() which never nukes the Vector<State>'s backing store.
This means that we always have capacity for at least 16 states in each GraphicsContext that has ever save()d.
Since canvas elements have a persistent GraphicsContext, this adds up to a bunch of memory with multiple canvases around.

[Andreas Kling]

Created attachment 254604 [details]
Patch

[Geoffrey Garen]

Comment on attachment 254604 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=254604&action=review

r=me

> Source/WebCore/platform/graphics/GraphicsContext.cpp:140
> +    // Make sure we deallocate the state stack buffer when it goes empty.
> +    // Canvas elements will immediately save() again, but that goes into inline capacity.
> +    if (m_stack.isEmpty())
> +        m_stack.clear();

Should Vector do this automatically?

[Geoffrey Garen]

To elaborate, I really hate it that std::vector does not do this automatically. At the limit, you have to add a call to clear to every client!

[Andreas Kling]

(In reply to comment #3)
> To elaborate, I really hate it that std::vector does not do this
> automatically. At the limit, you have to add a call to clear to every client!

I guess you mean WTF::Vector.
We can totes do that. Let's separate the issues though.

[Geoffrey Garen]

> > To elaborate, I really hate it that std::vector does not do this
> > automatically. At the limit, you have to add a call to clear to every client!
> 
> I guess you mean WTF::Vector.
> We can totes do that. Let's separate the issues though.

No, I mean that std::vector never ever shrinks until you call shrink_to_fit, which is super annoying, while WTF::Vector often shrinks automatically, but misses in this case.

[WebKit Commit Bot]

Comment on attachment 254604 [details]
Patch

Clearing flags on attachment: 254604

Committed r185396: <http://trac.webkit.org/changeset/185396>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.