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[web] Use Xvfb -displayfd and clean up Xvfb after Firefox test suites - #193510

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mdebbar:fix-firefox-xvfb-display
Sep 30, 2026
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auto-submit[bot] merged 2 commits into
flutter:masterfrom
mdebbar:fix-firefox-xvfb-display

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@mdebbar

@mdebbar mdebbar commented Sep 29, 2026

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Follow-up to #193187.

Firefox._ensureLinuxDisplay() previously spawned a detached Xvfb :99 process if /tmp/.X11-unix/X99 did not exist. When Swarming terminates a task with SIGKILL, the detached Xvfb :99 dies without unlinking /tmp/.X11-unix/X99 or /tmp/.X99-lock on the persistent host /tmp. Because File('/tmp/.X11-unix/X99').existsSync() returns true for a dead Unix domain socket inode, subsequent felt runs on that bot skip starting Xvfb and pass a dead DISPLAY=:99 to headless Firefox, causing firefox-dart2wasm-skwasm-ui to fail with:

Flutter Web: build dart2wasm/skwasm was skipped: Skwasm requires WebGL support; this browser does not provide it.
Flutter Web: no compatible build found for this browser.

Example CI failures:

This change:

  1. Launches Xvfb with -displayfd 1 instead of hardcoding :99, letting Xvfb pick an unused display (recovering automatically from stale dead sockets) and report the display number on stdout once ready to accept connections.
  2. Runs Xvfb as a managed child process and terminates it in FirefoxEnvironment.cleanup() (invoked inside RunSuiteStep.run()'s finally block).

Pre-launch Checklist

@flutter-dashboard flutter-dashboard Bot added the CICD Run CI/CD label Sep 29, 2026
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It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

@github-actions github-actions Bot added engine flutter/engine related. See also e: labels. platform-web Web applications specifically team-web Owned by Web platform team labels Sep 29, 2026

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Code Review

This pull request refactors the Xvfb startup and cleanup process for Firefox on Linux by dynamically reading the display number from stdout and ensuring proper process termination. It also moves the browser environment cleanup into a finally block during test suite execution. Feedback points out a potential unhandled asynchronous error if the display completer times out, suggesting stream subscription cancellation, and a race condition in process cleanup that could leak Xvfb if stopped before startup completes.

Comment thread engine/src/flutter/lib/web_ui/dev/firefox.dart
Comment thread engine/src/flutter/lib/web_ui/dev/firefox.dart
@mdebbar
mdebbar requested a review from kevmoo September 29, 2026 19:59
@mdebbar mdebbar added the autosubmit Merge PR when tree becomes green via auto submit App label Sep 30, 2026
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auto-submit Bot added this pull request to the merge queue Sep 30, 2026
Merged via the queue into flutter:master with commit 29bfd8c Sep 30, 2026
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@flutter-dashboard flutter-dashboard Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Sep 30, 2026
auto-submit Bot pushed a commit to flutter/packages that referenced this pull request Oct 1, 2026
…13104)

Manual roll requested by [email protected]

flutter/flutter@d649d2b...e89fd0a

2026-10-01 [email protected] Manual roll ICU from 6ebb40c59477 to 5aa526207171 (2 revisions) (flutter/flutter#193661)
2026-10-01 [email protected] fix(web): hash source maps before rewriting sourceMappingURL with --web-content-hash (flutter/flutter#193614)
2026-10-01 [email protected] [flutter_tools] Bootstrap DeviceManager in ToolDependencies (flutter/flutter#193524)
2026-10-01 [email protected] [wasm] Set flutter_runtime_mode in tools/gn to_gn_wasm_args (flutter/flutter#193407)
2026-10-01 [email protected] Remove remaining `download_jdk` references (flutter/flutter#193562)
2026-10-01 [email protected] Synchronize dart2wasm feature probes in roll script and flutter_bootstrap.js (flutter/flutter#193271)
2026-10-01 [email protected] [web] Unskip web tests that now pass in gestures, services, and widgets (flutter/flutter#193512)
2026-10-01 [email protected] Roll Fuchsia Test Scripts from whZAV1mfT-Rdc0rQ8... to fCNknap4ZI0AMcvIf... (flutter/flutter#193640)
2026-10-01 [email protected] Roll Skia from 0575a37d0619 to f2d68e0b8863 (2 revisions) (flutter/flutter#193621)
2026-10-01 [email protected] perf(widgets): use const <Never>{} in InheritedModelElement and avoid redundant casts in RenderObjectElement.update (flutter/flutter#192913)
2026-10-01 [email protected] [web] Unskip and strengthen missing glyph tofu test on Wimp (flutter/flutter#193426)
2026-10-01 [email protected] [flutter_tools] Fix `flutter drive -d chrome` hanging on web (flutter/flutter#193459)
2026-10-01 [email protected] [web] Fix hang when Chromium cannot bind remote debugging port (flutter/flutter#193461)
2026-10-01 [email protected] [flutter_tools] Bundle data assets from hooks in flutter test (flutter/flutter#193435)
2026-10-01 [email protected] Roll Packages from 0ba9a82 to d5ec6db (11 revisions) (flutter/flutter#193641)
2026-10-01 [email protected] Revert: [flutter_tools] Fix DTD "Stream already subscribed" error and wait for analysis over DTD in widget preview (flutter/flutter#193637)
2026-10-01 [email protected] Roll Skia from 6182a3cf8f98 to 0575a37d0619 (5 revisions) (flutter/flutter#193613)
2026-10-01 [email protected] [flutter_tools] Fix DTD "Stream already subscribed" error and wait for analysis over DTD in widget preview (flutter/flutter#192930)
2026-09-30 [email protected] [Impeller] Sample the render target rect in offscreen advanced blends (flutter/flutter#192988)
2026-09-30 [email protected] Roll Skia from 01524014dff5 to 6182a3cf8f98 (11 revisions) (flutter/flutter#193594)
2026-09-30 [email protected] [web] Use Xvfb -displayfd and clean up Xvfb after Firefox test suites (flutter/flutter#193510)
2026-09-30 [email protected] Fixes bug where sibling node fail to update size (flutter/flutter#191220)
2026-09-30 [email protected] Roll Skia from c7b323126bf0 to 01524014dff5 (3 revisions) (flutter/flutter#193577)
2026-09-30 [email protected] Remove some Undefined Behavior from run_customer_testing_tests.dart. (flutter/flutter#193582)
2026-09-30 [email protected] Fix pointer id/coordinate mismatch in Android platform view multi-touch (flutter/flutter#191631)
2026-09-30 [email protected] Roll Packages from 3c6ce59 to 0ba9a82 (11 revisions) (flutter/flutter#193578)
2026-09-30 [email protected] Fix unresolved doc comment references in dev/ tooling (flutter/flutter#193501)

If this roll has caused a breakage, revert this CL and set the roller
to dry run mode using the controls here:
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Please CC [email protected],[email protected] on the revert to ensure that a human
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