[webkit-dev] setTimeout as browser speed throttle

[Rob Burns]

Hi Darin,

On Oct 3, 2008, at 9:37 AM, Darin Fisher wrote:

> On Thu, Oct 2, 2008 at 10:36 PM, Maciej Stachowiak <mjs at apple.com>  
> wrote:
>
> On Oct 2, 2008, at 10:09 PM, Darin Fisher wrote:
>
>> On Thu, Oct 2, 2008 at 9:58 PM, Maciej Stachowiak <mjs at apple.com>  
>> wrote:
>>
>
>> (I don't understand your comment about not having to have it on all  
>> the time.  Surely if a page is asking for a fast setTimeout  
>> repeatedly, it would be on "all the time.")
>>
>> My understanding is that timeBeinPeriod(1) is currently on all the  
>> time in Chrome, even when no short-delay timers are currently  
>> pending, thus leading to constant greater power consumption. But  
>> there is no need for it to be on when there are not fast timers  
>> pending. See WebCore/platform/win/SharedTimerWin.cpp. I think that  
>> is a technically better approach than switching based on power  
>> management state. Feedback welcome, though, and perhaps you will  
>> still come to a different conclusion.
>>
>> I think that is a good idea too, but it doesn't help when a fast  
>> setInterval is active.
>
> That is true. With the webkit.org version of SharedTimerWin, though,  
> you can at least close the problematic tab when you hear your fan  
> spin up and stop suffering any power drain. It may be that running  
> slower is a better option.
>
>
> Yeah, that's the trade off.  Close the offending tab or let it run,  
> but more slowly.

Another option, would be to halt timers for all unexposed tabs (i.e.,  
tabs in windows that are not the frontmost tab). Are there use-cases  
or sites that would break with such behavior? The reason I raise this  
option is that the loaded page represents important state to the user,  
but when it is buried on a window, it is probably not necessary for it  
to be actively responding to timer callbacks. Closing the tab saves  
battery life, but burying the tab behind another tab would be  
preferable for the user (a mobile user that may not be online when  
that important state represented by the page loaded in the tab is  
sought again).

Take care,
Rob
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