202655 2019-10-07 14:36:18 -0700 iOS Safari: timestamps can be identical for consecutive rAF callbacks 2025-09-13 17:35:27 -0700 1 1 1 Unclassified WebKit Layout and Rendering Safari 12 Unspecified Unspecified RESOLVED WORKSFORME InRadar P2 Normal --- 1 nolan webkit-unassigned ahmad.saleem792 bfulgham dino graouts sabouhallawa simon.fraser webkit-bug-importer zalan oldest_to_newest 1577518 0 380363 nolan 2019-10-07 14:36:18 -0700 Created attachment 380363 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. 1577521 1 webkit-bug-importer 2019-10-07 14:52:00 -0700 <rdar://problem/56051818> 2141638 2 ahmad.saleem792 2025-09-08 10:02:10 -0700 @Nolan - is it still reproducing for you? I tried to reproduce by refreshing test page multiple times on iOS 26 Beta with latest build and I am unable to reproduce (+0) case. 2142809 3 nolan 2025-09-13 17:27:41 -0700 @Ahmad I moved my repro to a Codepen [1] and agree that I cannot repro on iOS Safari 18.6.2. FWIW I also could not repro in Safari Technology Preview 227 or GNOME Web 46.5. [1]: https://codepen.io/nolanlawson-the-selector/pen/GgpbBRW?editors=1010 2142810 4 ahmad.saleem792 2025-09-13 17:35:27 -0700 (In reply to Nolan Lawson from comment #3) > @Ahmad I moved my repro to a Codepen [1] and agree that I cannot repro on > iOS Safari 18.6.2. FWIW I also could not repro in Safari Technology Preview > 227 or GNOME Web 46.5. > > [1]: https://codepen.io/nolanlawson-the-selector/pen/GgpbBRW?editors=1010 Thanks for confirming Nolan, please keep on filing bug and CC me, happy to look at them. :-) Will keep this repo in mind as well. 380363 2019-10-07 14:36:18 -0700 2019-10-07 14:36:18 -0700 Repro HTML page index.html text/html 843 nolan PCFET0NUWVBFIGh0bWw+CjxodG1sIGxhbmc9ImVuIj4KPGhlYWQ+CiAgPG1ldGEgY2hhcnNldD0i VVRGLTgiPgogIDxtZXRhIG5hbWU9InZpZXdwb3J0IiBjb250ZW50PSJ3aWR0aD1kZXZpY2Utd2lk dGgiPgogIDx0aXRsZT5UZXN0IHJBRiB0aW1pbmc8L3RpdGxlPgo8L2hlYWQ+Cjxib2R5Pgo8aDE+ VGVzdCByQUYgdGltaW5nPC9oMT4KPHByZSBpZD0iZGlzcGxheSI+PC9wcmU+CjxzY3JpcHQ+CiAg d2luZG93LmFkZEV2ZW50TGlzdGVuZXIoJ2xvYWQnLCBmdW5jdGlvbiAoKSB7CiAgICB2YXIgdGlt ZXN0YW1wcyA9IFtdCgogICAgZnVuY3Rpb24gb25SYWYgKHRzKSB7CiAgICAgIHRpbWVzdGFtcHMu cHVzaCh0cykKICAgICAgaWYgKHRpbWVzdGFtcHMubGVuZ3RoIDwgMzApIHsKICAgICAgICByZXF1 ZXN0QW5pbWF0aW9uRnJhbWUob25SYWYpCiAgICAgIH0gZWxzZSB7CiAgICAgICAgc2hvd1Jlc3Vs dHMoKQogICAgICB9CiAgICB9CgogICAgZnVuY3Rpb24gc2hvd1Jlc3VsdHMgKCkgewogICAgICB2 YXIgZGlzcGxheSA9IGRvY3VtZW50LmdldEVsZW1lbnRCeUlkKCdkaXNwbGF5JykKICAgICAgZm9y ICh2YXIgaSA9IDA7IGkgPCB0aW1lc3RhbXBzLmxlbmd0aDsgaSsrKSB7CiAgICAgICAgZGlzcGxh eS5pbm5lckhUTUwgKz0gdGltZXN0YW1wc1tpXSArCiAgICAgICAgICAgICAgICAoaSA+IDAgPyAo JyAoKycgKyAodGltZXN0YW1wc1tpXSAtIHRpbWVzdGFtcHNbaSAtIDFdKSArICcpJykgOiAnJykg KwogICAgICAgICAgICAgICAgJ1xuJwogICAgICB9CiAgICB9CgogICAgcmVxdWVzdEFuaW1hdGlv bkZyYW1lKG9uUmFmKQogIH0pCjwvc2NyaXB0Pgo8L2JvZHk+CjwvaHRtbD4K