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Re: JavaScript-Driven Accelerated Animations

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Wed, 02 Oct 2013 17:15:49 -0400
Message-ID: <524C8D05.5080308@mit.edu>
To: www-style@w3.org
On 10/2/13 2:28 PM, Ian Vollick wrote:
>     /Why can't we update CSS properties from a worker thread?

In practical terms, because style system data structures tend to not be 
threadsafe in UAs.

But more conceptually, because that would violate the main thread's 
run-to-completion semantics: setting the value on the main thread and 
then reading it might not read the same value if in the meantime the 
background thread has written the value.

>     CSS properties could effect a style recalc or a layout and those
>     operations must happen on the main thread.

Those happen async anyway, so aren't a problem per se if we're not 
worried about a background thread touching the CSSOM.

That said, reading your proposal it sounds like you're basically 
proposing sugar for computing the values of properties in a worker but 
then actually setting them on the main thread, right?  At least that's 
my best guess for what the asynchronous proxies are meant to do?

-Boris
Received on Wednesday, 2 October 2013 21:16:17 UTC

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