1710357 - No "snap back" effect when the page has a slow script warning

Status: NEW

(Core :: Panning and Zooming, defect, P3)

Description

[Martin Balfanz [:mbalfanz]]

I just ran into a situation on Slack where I could scroll the channel sidebar endlessly into the overscroll area. There was no snap back effect. Shortly after, I got a slow script warning. I assume this is related.

Unfortunately I don't have easy STR, but wanted to track this in case it comes up again.

Comment 1

[Hiroyuki Ikezoe (:hiro)]

If there are wheel event listeners, APZ waits for the responses from the event listener to see if the event can be used for APZ or not, so maybe that's the case? I haven't found suspicious event listeners there though.

Comment 2

[Botond Ballo [:botond]]

There is a timeout of 600ms on that wait, so it shouldn't, in and of itself, be causing us to get stuck in overscroll.

I think the more likely explanation is that some combination of events / responses causes us to get stuck in a bad state, as in bug 1707217.

Comment 3

[Hiroyuki Ikezoe (:hiro)]

Attachment: A trial to simulate the busy situation

Here is an artificial version of simulating slow script.

After one second, this file tries to generate 30s hang. During the hang I am still be able to overscroll and see snap back animations.

Comment 4

[Hiroyuki Ikezoe (:hiro)]

Blocking overscroll-post since we have no idea how this could happen. My current hypothesis is that the scroller in question was inactive at that moment when we try to scroll via APZ, then we couldn't make it active due to the slow script on the main-thread?

Comment 5

[Botond Ballo [:botond]]

(In reply to Hiroyuki Ikezoe (:hiro) from comment #4)

My current hypothesis is that the scroller in question was inactive at that moment when we try to scroll via APZ, then we couldn't make it active due to the slow script on the main-thread?

I don't think we could overscroll it in the first place if it was inactive.