This issue is blocking some accessibility improvements in Electron-based apps, e.g. VSCode.

See https://bugs.chromium.org/p/chromium/issues/detail?id=580955 and https://github.com/Microsoft/vscode/issues/41423 (in particular, https://github.com/Microsoft/vscode/issues/26730#issuecomment-302929299 - "Chromium stalls for seconds if we write large quantities of text to the textarea [when accessibility support is turned on]") for details.

Using "--force-renderer-accessibility" and the attached test.html,
bisected to c101cb728aecdd2bb77d29ebe8deaee47261f65e
"Accessibility should always serialize an entire block when something changes."
Landed in 69.0.3497.0

Able to reproduce this issue on Windows 10, Mac OS 10.13.3 and Ubuntu 16.04 on the latest Canary 70.0.3507.0 and latest Dev 69.0.3497.12 as per comment #3.

Bisect Information:
===================
Good Build: 69.0.3496.0
Bad Build : 69.0.3497.0

As per comment #3, suspecting the below change:
Reviewed-on: https://chromium-review.googlesource.com/1062661

dmazzoni@ Please check and confirm if this issue is related to your change, else help us in assigning to the right owner.

Adding 'ReleaseBlock-Stable' as this is a recent regression. Please feel free to remove if it is not applicable.

Thanks..

I want to see if https://chromium-review.googlesource.com/c/chromium/src/+/1152180 fixes this issue too.

M69 Stable promotion is coming VERY soon. Your bug is labelled as Stable ReleaseBlock, pls make sure to land the fix and request a merge into the release branch ASAP. Thank you.

dmazzoni@ I can still reproduce this issue on the latest trunk build (Version 70.0.3522.0 - https://crrev.com/582628), so your other change doesn't seem to have fixed it.

M69 Stable promotion is coming VERY soon. Your bug is labelled as Stable ReleaseBlock, pls make sure to land the fix and request a merge into the release branch ASAP. Thank you.

Working on a revert here:

https://chromium-review.googlesource.com/c/chromium/src/+/1174851

Pls request a merge to M69 once revert listed at #12 is landed in canary and looks safe to merge to M69. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b53fffcc225fd0f37ab7f56ba9f075f319d5e439

commit b53fffcc225fd0f37ab7f56ba9f075f319d5e439
Author: Dominic Mazzoni <dmazzoni@chromium.org>
Date: Wed Aug 15 06:49:41 2018

Roll back code that serialized at the CSS block level due to performance.

crrev.com/c/1062661 made it so that any time an accessibility node changes,
we re-serialize the entire CSS block it's contained in - while this fixed
some correctness issues, it introduced a performance regression that's
too significant to ignore.

This change rolls back the fix for now until we can find a way to fix it
that doesn't impact performance.

TBR=dtseng@chromium.org

Bug:  868830 , 865621,  843746 
Change-Id: I900a4e6ba796608974e881f091b99b0d45c09536
Reviewed-on: https://chromium-review.googlesource.com/1174851
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583182}
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/browser/accessibility/line_layout_browsertest.cc
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/renderer/accessibility/render_accessibility_impl.cc
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/test/data/accessibility/event/aria-combo-box-next-expected-win.txt
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/test/data/accessibility/event/listbox-next-expected-win.txt
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/test/data/accessibility/event/menulist-collapse-expected-mac.txt
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/test/data/accessibility/event/menulist-collapse-expected-win.txt
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/test/data/accessibility/event/menulist-focus-expected-mac.txt
[modify] https://crrev.com/b53fffcc225fd0f37ab7f56ba9f075f319d5e439/content/test/data/accessibility/event/menulist-focus-expected-win.txt

Can confirm that https://crrev.com/583195 does not exhibit the issue. Thank you.

As noted in #15, I can confirm that the regression introduced at c101cb728aecdd2bb77d29ebe8deaee47261f65e has been fixed.

However, the underlying performance issue which is blocking accessibility improvements in VSCode still exists. (I was confused and thought the regression was the issue we were facing in VSCode, but it can't be, since it never made it to Electron.)


Here are steps to reproduce the underlying issue:

1. Turn on Chrome's accessbility support by going to chrome://accessibility and ticking 'Native accessibility API support' and 'Web accessibility'

2. On the same page, tick 'Text metrics'. (This is turned on by default when a screen reader, e.g. NVDA, is used.)

3. Open a page with a large <textarea> (10,000 lines)

4. The page is instantly unreponsive & hangs. No input events are executed -- all time out (see trace).


This triggers specifically when 'text metrics' is on. It seems there's some sort of infinite loop. See the attached GIF and trace from chrome://tracing.

(I suppose it might be OK to remove the Release Block now, since this underlying issue has existed for at least 2 years.)

Deleted: test10k.html 165 bytes

test10k.html 165 bytes View Download

Deleted: text-metrics-hang.gif 216 KB

	text-metrics-hang.gif 216 KB View Download

Deleted: trace_text-metrics-hang.json.gz 1.4 MB

trace_text-metrics-hang.json.gz 1.4 MB Download

Hi George - I filed a new bug -  http://crbug.com/875344  - for the 10k text area. I'll keep this bug for the regression release blocker. Thanks.

Requesting merge to M69, since we've verified that it fixes the regrsesion.

This bug requires manual review: M69 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), kariahda@(iOS), cindyb@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Approving merge to M69 branch 3497 based on comment #18. Please merge. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5c376201983d79d88a1650b108a83888853404d3

commit 5c376201983d79d88a1650b108a83888853404d3
Author: Dominic Mazzoni <dmazzoni@chromium.org>
Date: Fri Aug 17 18:10:49 2018

Merge to M69: Roll back code that serialized at the CSS block level due to performance.

crrev.com/c/1062661 made it so that any time an accessibility node changes,
we re-serialize the entire CSS block it's contained in - while this fixed
some correctness issues, it introduced a performance regression that's
too significant to ignore.

This change rolls back the fix for now until we can find a way to fix it
that doesn't impact performance.

TBR=dtseng@chromium.org

Bug:  868830 , 865621,  843746 
Change-Id: I900a4e6ba796608974e881f091b99b0d45c09536
Reviewed-on: https://chromium-review.googlesource.com/1174851
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#583182}(cherry picked from commit b53fffcc225fd0f37ab7f56ba9f075f319d5e439)
Reviewed-on: https://chromium-review.googlesource.com/1180141
Cr-Commit-Position: refs/branch-heads/3497@{#691}
Cr-Branched-From: 271eaf50594eb818c9295dc78d364aea18c82ea8-refs/heads/master@{#576753}
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/browser/accessibility/line_layout_browsertest.cc
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/renderer/accessibility/render_accessibility_impl.cc
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/test/data/accessibility/event/aria-combo-box-next-expected-win.txt
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/test/data/accessibility/event/listbox-next-expected-win.txt
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/test/data/accessibility/event/menulist-collapse-expected-mac.txt
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/test/data/accessibility/event/menulist-collapse-expected-win.txt
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/test/data/accessibility/event/menulist-focus-expected-mac.txt
[modify] https://crrev.com/5c376201983d79d88a1650b108a83888853404d3/content/test/data/accessibility/event/menulist-focus-expected-win.txt