W3C home > Mailing lists > Public > public-web-perf@w3.org > July 2011

Re: [Efficient Script Yielding] - Clamping

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Sat, 02 Jul 2011 23:54:43 -0400
Message-ID: <4E0FE803.8010203@mit.edu>
To: public-web-perf@w3.org
On 7/2/11 1:34 PM, Kyle Simpson wrote:
> Another thought (quite possibly off base)... is the clamping done
> because of the inefficiency of a rapidly repeating script making changes
> to the DOM (or styles) and requiring repaints/reflows?

It's done because some pages expect repeated setTimeout(0) to do 
something "slowly enough" (e.g. scroll a message by that the user can read).

That's for foreground tab clamping; background tab is just a matter of 
preventing web pages the user is not looking at from using resources by 

> If a tightly running loop doesn't do anything but change values in JS variables
> (doesn't affect the DOM/CSS)

Defined how?  If a script reads/writes properties on the Window, is that 
affecting the DOM/CSS?

> is clamping as necessary? If it's less
> necessary, perhaps browsers could allow the bubble-sort use-case (the
> yield step in an algorithm) to run un-clamped, but if a piece of code
> affects the DOM/CSS in any way, then clamping kicks in?

This sounds like a very fragile setup to me, where code may or may not 
get clamped for very mysterious reasons.

Received on Sunday, 3 July 2011 03:55:11 UTC

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