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[Linux] Wait for frames to be rendered before using them in another context by robert-ancell · Pull Request #192094 · flutter/flutter · GitHub
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[Linux] Wait for frames to be rendered before using them in another context - #192094

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robert-ancell:linux-gl-finish
Sep 1, 2026
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[Linux] Wait for frames to be rendered before using them in another context#192094
robert-ancell merged 1 commit into
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robert-ancell:linux-gl-finish

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@robert-ancell robert-ancell commented Sep 1, 2026

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Frames are rendered on the raster thread using the engine's OpenGL context, then read by whoever presents them using a different context. Sharing a texture between contexts requires the rendering to have completed before the other context uses it; a flush only guarantees the commands have been submitted. The frame could therefore be read while it was still being rendered, which can show a partially rendered frame and can put drivers into a state where later operations fail.

Two paths read a frame from another context:

  • fl_opengl_frame_composite() when the frame is shareable, which is drawn by GTK on the main thread using GDK's context.
  • fl_view_renderer_subsurface_present_layers(), which presents using the subsurface's own context. Making that context current only flushes the engine's context.

Wait for the rendering to complete in both. The remaining case, a frame that isn't shareable, is copied out with glReadPixels(), which already waits for the rendering to complete.

See #191775

@robert-ancell
[Linux] Wait for frames to be rendered before using them in another c…
8374bff 
…ontext

Frames are rendered on the raster thread using the engine's OpenGL
context, then read by whoever presents them using a different context.
Sharing a texture between contexts requires the rendering to have
completed before the other context uses it; a flush only guarantees the
commands have been submitted. The frame could therefore be read while it
was still being rendered, which can show a partially rendered frame and
can put drivers into a state where later operations fail.

Two paths read a frame from another context:

- fl_opengl_frame_composite() when the frame is shareable, which is
  drawn by GTK on the main thread using GDK's context.
- fl_view_renderer_subsurface_present_layers(), which presents using the
  subsurface's own context. Making that context current only flushes the
  engine's context.

Wait for the rendering to complete in both. The remaining case, a frame
that isn't shareable, is copied out with glReadPixels(), which already
waits for the rendering to complete.

See flutter#191775
@robert-ancell
robert-ancell requested a review from a team as a code owner September 1, 2026 03:26
@flutter-dashboard flutter-dashboard Bot added the CICD Run CI/CD label Sep 1, 2026
@github-actions github-actions Bot added engine flutter/engine related. See also e: labels. platform-linux Building on or for Linux specifically a: desktop Running on desktop team-linux Owned by the Linux platform team labels Sep 1, 2026
gemini-code-assist[bot]
gemini-code-assist Bot reviewed Sep 1, 2026
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Code Review

This pull request introduces synchronization using glFinish() in fl_opengl_frame.cc and fl_view_renderer_subsurface.cc to ensure rendering completes before textures are shared across different OpenGL contexts, and adds corresponding unit tests in fl_opengl_frame_test.cc with mocked epoxy calls. Feedback on these changes highlights that calling glFinish() can cause correctness issues depending on the active context and introduces performance bottlenecks by stalling the CPU thread; using OpenGL Sync Objects (Fences) is recommended instead for efficient GPU-side synchronization.

Comment thread engine/src/flutter/shell/platform/linux/fl_opengl_frame.cc Resolved
Comment thread engine/src/flutter/shell/platform/linux/fl_view_renderer_subsurface.cc Resolved
@robert-ancell

robert-ancell commented Sep 1, 2026

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Follow up in #192098 to add fence support which is more efficient.

@robert-ancell robert-ancell mentioned this pull request Sep 1, 2026
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mattkae
mattkae approved these changes Sep 1, 2026
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👍

@robert-ancell
robert-ancell added this pull request to the merge queue Sep 1, 2026
Merged via the queue into flutter:master with commit 6dad922 Sep 1, 2026
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@robert-ancell
robert-ancell deleted the linux-gl-finish branch September 1, 2026 23:05
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auto-submit Bot pushed a commit to flutter/packages that referenced this pull request Sep 4, 2026
@engine-flutter-autoroll
Roll Flutter from 0cbd1a4be0a4 to 70797e15325e (27 revisions) (#12727)
1240bb5 
flutter/flutter@0cbd1a4...70797e1

2026-09-02 bkonyi@google.com [analysis] Upgrade package:analyzer to 14.3.0 and enable custom plugin compilation (flutter/flutter#191590)
2026-09-02 engine-flutter-autoroll@skia.org Roll Dart SDK from d8d7869d8031 to 9a8fbde80f6c (1 revision) (flutter/flutter#192179)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from dec311244db4 to ae22da2e8308 (1 revision) (flutter/flutter#192177)
2026-09-02 bkonyi@google.com [tool] Migrate DoctorCommand to modular dependency injection (flutter/flutter#190758)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 482b7e285244 to dec311244db4 (3 revisions) (flutter/flutter#192161)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 28447e9fb8d5 to 482b7e285244 (3 revisions) (flutter/flutter#192157)
2026-09-02 34465683+rkishan516@users.noreply.github.com feat: Add placeholder to DecorationImage (flutter/flutter#191528)
2026-09-02 papmodern14@gmail.com [Android] Do not schedule engine frames on a detached FlutterJNI (flutter/flutter#191204)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 3a242fb7cdb3 to 28447e9fb8d5 (1 revision) (flutter/flutter#192145)
2026-09-02 engine-flutter-autoroll@skia.org Roll Dart SDK from 9164def35347 to d8d7869d8031 (2 revisions) (flutter/flutter#192144)
2026-09-02 74458687+anazr9@users.noreply.github.com Add FadeInImageTransition.fadeInOver to fade the image in over the placeholder (flutter/flutter#186246)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 63d13ec4df6d to 3a242fb7cdb3 (9 revisions) (flutter/flutter#192138)
2026-09-02 bkonyi@google.com [flutter_tools] Add --no-plugins flag and disable plugins for benchmark (flutter/flutter#192129)
2026-09-02 bkonyi@google.com [tool] Migrate ChannelCommand to modular dependency injection (flutter/flutter#190751)
2026-09-01 46920873+gabrimatic@users.noreply.github.com Add mouseCursor to RawScrollbar (flutter/flutter#185750)
2026-09-01 ksanaullah383.khan@gmail.com Fix self-comparison and assert typos in TestSemantics (flutter/flutter#191938)
2026-09-01 robert.ancell@canonical.com [Linux] Wait for frames to be rendered before using them in another context (flutter/flutter#192094)
2026-09-01 jacksongardner@google.com [wimp] Turn on multithreading for wimp. (flutter/flutter#191747)
2026-09-01 engine-flutter-autoroll@skia.org Roll Skia from 3911a1fe7f7a to 63d13ec4df6d (6 revisions) (flutter/flutter#192125)
2026-09-01 jason-simmons@users.noreply.github.com Remove the redundant flutter/shell/platform/android:robolectric_tests build target (flutter/flutter#192117)
2026-09-01 AfzalivE@users.noreply.github.com [iOS] Preserve semantics parents after reparenting (flutter/flutter#189686)
2026-09-01 bkonyi@google.com [flutter_tools] Report preview reload timing analytics in LspPreviewDetector (flutter/flutter#192120)
2026-09-01 bkonyi@google.com [flutter_tools] Implement Templates slice and flutter create integration (flutter/flutter#191748)
2026-09-01 louisehsu@google.com Uiscene migrate add2app hosts (flutter/flutter#191847)
2026-09-01 engine-flutter-autoroll@skia.org Roll Packages from d642322 to 7a7912f (8 revisions) (flutter/flutter#192119)
2026-09-01 zhongliu88889@gmail.com [web] Anchor flt-semantics-host at 0,0 to fix WebKit semantics offset (flutter/flutter#190486)
2026-09-01 jason-simmons@users.noreply.github.com Replace Shell::WaitForFirstFrame with an asynchronous API that matches the Shell threading model (flutter/flutter#191841)

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 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
victorsanni pushed a commit to victorsanni/packages that referenced this pull request Sep 9, 2026
@engine-flutter-autoroll @victorsanni
Roll Flutter from 0cbd1a4be0a4 to 70797e15325e (27 revisions) (flutte…
2822f8e 
…r#12727)

flutter/flutter@0cbd1a4...70797e1

2026-09-02 bkonyi@google.com [analysis] Upgrade package:analyzer to 14.3.0 and enable custom plugin compilation (flutter/flutter#191590)
2026-09-02 engine-flutter-autoroll@skia.org Roll Dart SDK from d8d7869d8031 to 9a8fbde80f6c (1 revision) (flutter/flutter#192179)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from dec311244db4 to ae22da2e8308 (1 revision) (flutter/flutter#192177)
2026-09-02 bkonyi@google.com [tool] Migrate DoctorCommand to modular dependency injection (flutter/flutter#190758)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 482b7e285244 to dec311244db4 (3 revisions) (flutter/flutter#192161)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 28447e9fb8d5 to 482b7e285244 (3 revisions) (flutter/flutter#192157)
2026-09-02 34465683+rkishan516@users.noreply.github.com feat: Add placeholder to DecorationImage (flutter/flutter#191528)
2026-09-02 papmodern14@gmail.com [Android] Do not schedule engine frames on a detached FlutterJNI (flutter/flutter#191204)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 3a242fb7cdb3 to 28447e9fb8d5 (1 revision) (flutter/flutter#192145)
2026-09-02 engine-flutter-autoroll@skia.org Roll Dart SDK from 9164def35347 to d8d7869d8031 (2 revisions) (flutter/flutter#192144)
2026-09-02 74458687+anazr9@users.noreply.github.com Add FadeInImageTransition.fadeInOver to fade the image in over the placeholder (flutter/flutter#186246)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 63d13ec4df6d to 3a242fb7cdb3 (9 revisions) (flutter/flutter#192138)
2026-09-02 bkonyi@google.com [flutter_tools] Add --no-plugins flag and disable plugins for benchmark (flutter/flutter#192129)
2026-09-02 bkonyi@google.com [tool] Migrate ChannelCommand to modular dependency injection (flutter/flutter#190751)
2026-09-01 46920873+gabrimatic@users.noreply.github.com Add mouseCursor to RawScrollbar (flutter/flutter#185750)
2026-09-01 ksanaullah383.khan@gmail.com Fix self-comparison and assert typos in TestSemantics (flutter/flutter#191938)
2026-09-01 robert.ancell@canonical.com [Linux] Wait for frames to be rendered before using them in another context (flutter/flutter#192094)
2026-09-01 jacksongardner@google.com [wimp] Turn on multithreading for wimp. (flutter/flutter#191747)
2026-09-01 engine-flutter-autoroll@skia.org Roll Skia from 3911a1fe7f7a to 63d13ec4df6d (6 revisions) (flutter/flutter#192125)
2026-09-01 jason-simmons@users.noreply.github.com Remove the redundant flutter/shell/platform/android:robolectric_tests build target (flutter/flutter#192117)
2026-09-01 AfzalivE@users.noreply.github.com [iOS] Preserve semantics parents after reparenting (flutter/flutter#189686)
2026-09-01 bkonyi@google.com [flutter_tools] Report preview reload timing analytics in LspPreviewDetector (flutter/flutter#192120)
2026-09-01 bkonyi@google.com [flutter_tools] Implement Templates slice and flutter create integration (flutter/flutter#191748)
2026-09-01 louisehsu@google.com Uiscene migrate add2app hosts (flutter/flutter#191847)
2026-09-01 engine-flutter-autoroll@skia.org Roll Packages from d642322 to 7a7912f (8 revisions) (flutter/flutter#192119)
2026-09-01 zhongliu88889@gmail.com [web] Anchor flt-semantics-host at 0,0 to fix WebKit semantics offset (flutter/flutter#190486)
2026-09-01 jason-simmons@users.noreply.github.com Replace Shell::WaitForFirstFrame with an asynchronous API that matches the Shell threading model (flutter/flutter#191841)

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 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
victorsanni pushed a commit to victorsanni/packages that referenced this pull request Sep 9, 2026
@engine-flutter-autoroll @victorsanni
Roll Flutter from 0cbd1a4be0a4 to 70797e15325e (27 revisions) (flutte…
2ee1685 
…r#12727)

flutter/flutter@0cbd1a4...70797e1

2026-09-02 bkonyi@google.com [analysis] Upgrade package:analyzer to 14.3.0 and enable custom plugin compilation (flutter/flutter#191590)
2026-09-02 engine-flutter-autoroll@skia.org Roll Dart SDK from d8d7869d8031 to 9a8fbde80f6c (1 revision) (flutter/flutter#192179)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from dec311244db4 to ae22da2e8308 (1 revision) (flutter/flutter#192177)
2026-09-02 bkonyi@google.com [tool] Migrate DoctorCommand to modular dependency injection (flutter/flutter#190758)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 482b7e285244 to dec311244db4 (3 revisions) (flutter/flutter#192161)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 28447e9fb8d5 to 482b7e285244 (3 revisions) (flutter/flutter#192157)
2026-09-02 34465683+rkishan516@users.noreply.github.com feat: Add placeholder to DecorationImage (flutter/flutter#191528)
2026-09-02 papmodern14@gmail.com [Android] Do not schedule engine frames on a detached FlutterJNI (flutter/flutter#191204)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 3a242fb7cdb3 to 28447e9fb8d5 (1 revision) (flutter/flutter#192145)
2026-09-02 engine-flutter-autoroll@skia.org Roll Dart SDK from 9164def35347 to d8d7869d8031 (2 revisions) (flutter/flutter#192144)
2026-09-02 74458687+anazr9@users.noreply.github.com Add FadeInImageTransition.fadeInOver to fade the image in over the placeholder (flutter/flutter#186246)
2026-09-02 engine-flutter-autoroll@skia.org Roll Skia from 63d13ec4df6d to 3a242fb7cdb3 (9 revisions) (flutter/flutter#192138)
2026-09-02 bkonyi@google.com [flutter_tools] Add --no-plugins flag and disable plugins for benchmark (flutter/flutter#192129)
2026-09-02 bkonyi@google.com [tool] Migrate ChannelCommand to modular dependency injection (flutter/flutter#190751)
2026-09-01 46920873+gabrimatic@users.noreply.github.com Add mouseCursor to RawScrollbar (flutter/flutter#185750)
2026-09-01 ksanaullah383.khan@gmail.com Fix self-comparison and assert typos in TestSemantics (flutter/flutter#191938)
2026-09-01 robert.ancell@canonical.com [Linux] Wait for frames to be rendered before using them in another context (flutter/flutter#192094)
2026-09-01 jacksongardner@google.com [wimp] Turn on multithreading for wimp. (flutter/flutter#191747)
2026-09-01 engine-flutter-autoroll@skia.org Roll Skia from 3911a1fe7f7a to 63d13ec4df6d (6 revisions) (flutter/flutter#192125)
2026-09-01 jason-simmons@users.noreply.github.com Remove the redundant flutter/shell/platform/android:robolectric_tests build target (flutter/flutter#192117)
2026-09-01 AfzalivE@users.noreply.github.com [iOS] Preserve semantics parents after reparenting (flutter/flutter#189686)
2026-09-01 bkonyi@google.com [flutter_tools] Report preview reload timing analytics in LspPreviewDetector (flutter/flutter#192120)
2026-09-01 bkonyi@google.com [flutter_tools] Implement Templates slice and flutter create integration (flutter/flutter#191748)
2026-09-01 louisehsu@google.com Uiscene migrate add2app hosts (flutter/flutter#191847)
2026-09-01 engine-flutter-autoroll@skia.org Roll Packages from d642322 to 7a7912f (8 revisions) (flutter/flutter#192119)
2026-09-01 zhongliu88889@gmail.com [web] Anchor flt-semantics-host at 0,0 to fix WebKit semantics offset (flutter/flutter#190486)
2026-09-01 jason-simmons@users.noreply.github.com Replace Shell::WaitForFirstFrame with an asynchronous API that matches the Shell threading model (flutter/flutter#191841)

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 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
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