{{ message }}
[web] Use thread local strike caches in skwasm - #190048
Merged
auto-submit[bot] merged 13 commits intoAug 5, 2026
Merged
Conversation
github-actions
Bot
added
a: text input
ColeSpringer
marked this pull request as ready for review
July 27, 2026 00:48
![gemini-code-assist[bot]](https://avatars.githubusercontent.com/in/956858?s=60&v=4){kind=small}
Contributor
There was a problem hiding this comment.
Code Review
This pull request introduces support for 'wasm_use_pthreads' in the build configuration and adds a concurrent text layout and rasterization test. It also dispatches resource cache limit updates to the raster worker thread in Skwasm, making 'current_callback_id_' atomic to support multi-threaded access. The reviewer recommends persistently storing the resource cache limit on the surface rather than clearing it after the initial setup, ensuring the limit is preserved if the render context is recreated.
ColeSpringer
force-pushed
the
fix-skwasm-hybrid-pthreads-190039
branch
from
July 27, 2026 00:57
fa1d523 to
d64e4b3
Compare
Multithreaded skwasm was built with -sWASM_WORKERS but without -pthread, which links emscripten's single-threaded stub system libraries: every lock in Skia, FreeType, and libc++ was a no-op while two threads shared linear memory, corrupting the heap under concurrent text layout and rasterization. Add a wasm_use_pthreads GN arg that links the pthread-enabled "-mt" system libraries while still creating threads as wasm workers, and enable it for the skwasm toolchains. Also make the cross-thread callback id atomic, dispatch surface_setResourceCacheLimitBytes to the raster worker that owns the render context, and add a regression test driving concurrent text layout and rasterization. Fixes #190039
ColeSpringer
force-pushed
the
fix-skwasm-hybrid-pthreads-190039
branch
from
July 27, 2026 17:31
d64e4b3 to
3f0a645
Compare
Renzo-Olivares
removed
the
a: text input
github-actions
Bot
added
the
a: text input
Contributor
Contributor
|
Also, I was looking at the change which makes |
Contributor
Author
|
@eyebrowsoffire Went ahead and switched out the pthreads implementation with the skia flag you mentioned. Ran the tests with the flag off and the issue reappeared (tests failed). Running with the flag on resulted in all of the tests passing. |
harryterkelsen
self-requested a review
August 4, 2026 19:33
harryterkelsen
approved these changes
Aug 4, 2026
harryterkelsen
left a comment
harryterkelsen
left a comment
Contributor
There was a problem hiding this comment.
LGTM. I think it's safe to use the experimental flag here. According to discussions with the Skia team, the flag is mostly safe, but not turned on by default because it breaks specific Chrome non-standard use cases. We should be okay using it.
Contributor
|
Please update the title of the PR to reflect the actual fix (enabling the experimental flag) |
eyebrowsoffire
approved these changes
Aug 4, 2026
eyebrowsoffire
left a comment
eyebrowsoffire
left a comment
Contributor
There was a problem hiding this comment.
I agree with @harryterkelsen, I think we should actually just land this. As he mentioned, please update the PR description and title so that the commit message is accurate.
ColeSpringer
changed the title
Contributor
Author
|
PR title and description updated. |
harryterkelsen
added
the
autosubmit
flutter-dashboard
Bot
removed
the
autosubmit
This was referenced Aug 5, 2026
This was referenced Aug 5, 2026
This was referenced Aug 6, 2026
auto-submit Bot
pushed a commit
to flutter/packages
that referenced
this pull request
Aug 10, 2026
…12420) Manual roll requested by stuartmorgan@google.com flutter/flutter@b766512...27b0988 2026-08-05 kevmoo@users.noreply.github.com reland(tool): remove redundant --enable-experiment=record-use flag (flutter/flutter#190591) 2026-08-05 chris@bracken.jp Windows: Propagate enabled accessibility state (flutter/flutter#190507) 2026-08-05 engine-flutter-autoroll@skia.org Roll Fuchsia Test Scripts from ltbuIH9Z3T_yOuigu... to vcANVO8VIDQHasH1X... (flutter/flutter#190589) 2026-08-05 256906086+mvincentong@users.noreply.github.com Document frozen embedder API structs (flutter/flutter#186842) 2026-08-05 49402500+fahaddoc@users.noreply.github.com Document super call order for State.didChangeDependencies (flutter/flutter#185945) 2026-08-05 dkwingsmt@users.noreply.github.com Move examples of `flutter/widgets` widgets out from `flutter/material` (flutter/flutter#189532) 2026-08-05 93888664+ColeSpringer@users.noreply.github.com [web] Use thread local strike caches in skwasm (flutter/flutter#190048) 2026-08-05 43089218+chika3742@users.noreply.github.com doc: fix typo in see also section for PrimaryScrollController.maybeOf (flutter/flutter#190386) 2026-08-05 jason-simmons@users.noreply.github.com Migrate the shell unit tests from legacy Dart native functions to FFI (flutter/flutter#190473) 2026-08-05 47866232+chunhtai@users.noreply.github.com render proxy box now defaults baseline calculation to null (flutter/flutter#190269) 2026-08-05 36861262+QuncCccccc@users.noreply.github.com Update Widgets Localizations from Translation Console (flutter/flutter#190503) 2026-08-04 154381524+flutteractionsbot@users.noreply.github.com Revert: fix(tool): remove redundant --enable-experiment=record-use flag (flutter/flutter#190583) 2026-08-04 engine-flutter-autoroll@skia.org Roll Fuchsia Test Scripts from 1frGe_KltAJKkeyPg... to ltbuIH9Z3T_yOuigu... (flutter/flutter#190561) 2026-08-04 chris@bracken.jp iOS,macOS: add tsan and ubsan support for Swift (flutter/flutter#190497) 2026-08-04 34465683+rkishan516@users.noreply.github.com fix: update on_message_ to nullptr after window destroy so that dart gets destroy message (flutter/flutter#185807) 2026-08-04 bkonyi@google.com [flutter_tools] Gracefully handle locked Windows files during clean (flutter/flutter#190095) 2026-08-04 chris@bracken.jp iOS,macOS: make Logger thread-safe, conform to Sendable (flutter/flutter#190488) 2026-08-04 chris@bracken.jp iOS: Eliminate use of IOSContextNoop in platform view tests (reland) (flutter/flutter#190509) 2026-08-04 kevmoo@users.noreply.github.com fix(tool): remove redundant --enable-experiment=record-use flag (flutter/flutter#190475) 2026-08-04 awolff@google.com android_hardware_smoke_test: Detect blank image failures or EGL initialization warnings and retry (flutter/flutter#190110) 2026-08-04 30870216+gaaclarke@users.noreply.github.com Bumps text gamma on windows to match skia. (flutter/flutter#190477) 2026-08-04 engine-flutter-autoroll@skia.org Roll Skia from 48b58ee222f1 to a8583a0a2c11 (2 revisions) (flutter/flutter#190537) 2026-08-04 kevmoo@users.noreply.github.com [tool][web] Intercept dart2wasm errors & append JS migration footers (flutter/flutter#190476) 2026-08-04 dacoharkes@google.com [record_use] Migrate IconTreeShaker to `package:record_use` (flutter/flutter#190225) 2026-08-04 s4bre.py@gmail.com Handle unexpected exceptions during Azure metadata detection (flutter/flutter#189457) 2026-08-04 15619084+vashworth@users.noreply.github.com Fix merge conflict from flutter/flutter#190369 (flutter/flutter#190544) 2026-08-04 15619084+vashworth@users.noreply.github.com Prepare device support symbols (flutter/flutter#190369) 2026-08-04 engine-flutter-autoroll@skia.org Roll Packages from ac87e65 to 3498b9d (1 revision) (flutter/flutter#190532) 2026-08-04 engine-flutter-autoroll@skia.org Roll Skia from a08d918ebd6a to 48b58ee222f1 (11 revisions) (flutter/flutter#190527) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC stuartmorgan@google.com,tarrinneal@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
pull Bot
pushed a commit
to AbhiShake1/flutter
that referenced
this pull request
Aug 20, 2026
After flutter#190048, we no longer have multthreading issues with wimp, so we should turn multithreading on. This addresses flutter#178749
This was referenced Aug 20, 2026
pull Bot
pushed a commit
to safarmer/flutter
that referenced
this pull request
Aug 20, 2026
Reverts: [[wimp] Turn multithreading on for wimp.](flutter#190626) Initiated by: @bkonyi Reason for reverting: [failing Linux linux_web_engine_tests on tree](https://ci.chromium.org/ui/p/flutter/builders/prod/Linux%20linux_web_engine_tests/9022). Original PR Author: @eyebrowsoffire Reviewed By: @mdebbar The original PR description is provided below: After flutter#190048, we no longer have multthreading issues with wimp, so we should turn multithreading on. This addresses flutter#178749
GhagSagar23
pushed a commit
to GhagSagar23/flutter
that referenced
this pull request
Aug 20, 2026
Reverts: [[wimp] Turn multithreading on for wimp.](flutter#190626) Initiated by: @bkonyi Reason for reverting: [failing Linux linux_web_engine_tests on tree](https://ci.chromium.org/ui/p/flutter/builders/prod/Linux%20linux_web_engine_tests/9022). Original PR Author: @eyebrowsoffire Reviewed By: @mdebbar The original PR description is provided below: After flutter#190048, we no longer have multthreading issues with wimp, so we should turn multithreading on. This addresses flutter#178749
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
5 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Description
Multithreaded skwasm is built with
-sWASM_WORKERSbut without-pthread, whichlinks the single threaded emscripten system libraries where mutexes are no-ops.
Text layout on the main thread and the raster worker share the global
SkStrikeCache, so under heavy text churn the two threads corrupt the heap andthe tab ends up pinned at 100% CPU.
The fix is Skia's experimental thread local strike cache flag, enabled from a
constructor in
surface.cc. Each thread gets its own strike cache, so there is noshared state left to race on.
Two adjacent fixes:
context_lost_callback_id_was allocated on the worker by incrementingcurrent_callback_id_, which the main thread also increments. It is nowallocated on the main thread in
SetCanvas.surface_setResourceCacheLimitBytestouched the worker ownedGrDirectContextfrom the main thread. It now dispatches to the worker, and the value is stored
and reapplied when the render context is recreated. This also fixes a null deref
when Dart sets the limit before surface init.
Tests
New regression test
lib/web_ui/test/skwasm/concurrent_text_layout_raster_test.dart:text layout with never repeating font parameters on the main thread while the
worker rasterizes the previous frame, disposing everything per frame and toggling
the resource cache limit. Without the flag it fails 2 of 2 runs (one wasm timeout,
one hard page freeze); with it, 6 of 6 pass. The context loss suite passes 4 of 4,
covering the callback id and cache limit changes.
No golden churn is expected.
Fixes #190039
Possibly also fixes #184858, which looks like the same corruption from the dispose
path.
Pre-launch Checklist
///).