[Webkit-unassigned] [Bug 202655] New: iOS Safari: timestamps can be identical for consecutive rAF callbacks
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Mon Oct 7 14:36:18 PDT 2019
https://bugs.webkit.org/show_bug.cgi?id=202655
Bug ID: 202655
Summary: iOS Safari: timestamps can be identical for
consecutive rAF callbacks
Product: WebKit
Version: Safari 12
Hardware: Unspecified
OS: Unspecified
Status: NEW
Severity: Normal
Priority: P2
Component: Layout and Rendering
Assignee: webkit-unassigned at lists.webkit.org
Reporter: nolan at nolanlawson.com
CC: bfulgham at webkit.org, simon.fraser at apple.com,
zalan at apple.com
Created attachment 380363
--> https://bugs.webkit.org/attachment.cgi?id=380363&action=review
Repro HTML page
Consider a web page trying to measure framerate by using the timestamps passed in to requestAnimationFrame callbacks. Per the event loop spec (https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model) it seems that the timestamps should typically be ~16ms apart (and certainly >0ms apart), but on iOS Safari it's possible for them to be 0ms apart.
Here is a sample page to demonstrate: https://bl.ocks.org/nolanlawson/raw/99773cc8edc4115e6ba156a503dd2c41/
You might have to refresh the page a few times to reproduce, but often there will be one rAF callback whose timestamp is exactly the same as the previous one, e.g.:
12
24 (+12)
34 (+10)
34 (+0) <-- exactly the same as the last one
43 (+9)
So far this seems only reproducible on iOS Safari. I can repro on both iOS 12.4 and 13.0 (using a real iPhone for the first and a simulator for the second).
I'm not sure if the issue is with the timestamp or if the rAF callbacks are truly firing on the same turn of the event loop.
--
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.webkit.org/pipermail/webkit-unassigned/attachments/20191007/98783bcb/attachment.html>
More information about the webkit-unassigned
mailing list