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

robert-ancell · 2026-09-01T03:26:50Z

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

…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

gemini-code-assist

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.

robert-ancell · 2026-09-01T05:47:23Z

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

mattkae

👍

flutter/flutter@0cbd1a4...70797e1 2026-09-02 [email protected] [analysis] Upgrade package:analyzer to 14.3.0 and enable custom plugin compilation (flutter/flutter#191590) 2026-09-02 [email protected] Roll Dart SDK from d8d7869d8031 to 9a8fbde80f6c (1 revision) (flutter/flutter#192179) 2026-09-02 [email protected] Roll Skia from dec311244db4 to ae22da2e8308 (1 revision) (flutter/flutter#192177) 2026-09-02 [email protected] [tool] Migrate DoctorCommand to modular dependency injection (flutter/flutter#190758) 2026-09-02 [email protected] Roll Skia from 482b7e285244 to dec311244db4 (3 revisions) (flutter/flutter#192161) 2026-09-02 [email protected] Roll Skia from 28447e9fb8d5 to 482b7e285244 (3 revisions) (flutter/flutter#192157) 2026-09-02 [email protected] feat: Add placeholder to DecorationImage (flutter/flutter#191528) 2026-09-02 [email protected] [Android] Do not schedule engine frames on a detached FlutterJNI (flutter/flutter#191204) 2026-09-02 [email protected] Roll Skia from 3a242fb7cdb3 to 28447e9fb8d5 (1 revision) (flutter/flutter#192145) 2026-09-02 [email protected] Roll Dart SDK from 9164def35347 to d8d7869d8031 (2 revisions) (flutter/flutter#192144) 2026-09-02 [email protected] Add FadeInImageTransition.fadeInOver to fade the image in over the placeholder (flutter/flutter#186246) 2026-09-02 [email protected] Roll Skia from 63d13ec4df6d to 3a242fb7cdb3 (9 revisions) (flutter/flutter#192138) 2026-09-02 [email protected] [flutter_tools] Add --no-plugins flag and disable plugins for benchmark (flutter/flutter#192129) 2026-09-02 [email protected] [tool] Migrate ChannelCommand to modular dependency injection (flutter/flutter#190751) 2026-09-01 [email protected] Add mouseCursor to RawScrollbar (flutter/flutter#185750) 2026-09-01 [email protected] Fix self-comparison and assert typos in TestSemantics (flutter/flutter#191938) 2026-09-01 [email protected] [Linux] Wait for frames to be rendered before using them in another context (flutter/flutter#192094) 2026-09-01 [email protected] [wimp] Turn on multithreading for wimp. (flutter/flutter#191747) 2026-09-01 [email protected] Roll Skia from 3911a1fe7f7a to 63d13ec4df6d (6 revisions) (flutter/flutter#192125) 2026-09-01 [email protected] Remove the redundant flutter/shell/platform/android:robolectric_tests build target (flutter/flutter#192117) 2026-09-01 [email protected] [iOS] Preserve semantics parents after reparenting (flutter/flutter#189686) 2026-09-01 [email protected] [flutter_tools] Report preview reload timing analytics in LspPreviewDetector (flutter/flutter#192120) 2026-09-01 [email protected] [flutter_tools] Implement Templates slice and flutter create integration (flutter/flutter#191748) 2026-09-01 [email protected] Uiscene migrate add2app hosts (flutter/flutter#191847) 2026-09-01 [email protected] Roll Packages from d642322 to 7a7912f (8 revisions) (flutter/flutter#192119) 2026-09-01 [email protected] [web] Anchor flt-semantics-host at 0,0 to fix WebKit semantics offset (flutter/flutter#190486) 2026-09-01 [email protected] 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 [email protected] 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

…r#12727) flutter/flutter@0cbd1a4...70797e1 2026-09-02 [email protected] [analysis] Upgrade package:analyzer to 14.3.0 and enable custom plugin compilation (flutter/flutter#191590) 2026-09-02 [email protected] Roll Dart SDK from d8d7869d8031 to 9a8fbde80f6c (1 revision) (flutter/flutter#192179) 2026-09-02 [email protected] Roll Skia from dec311244db4 to ae22da2e8308 (1 revision) (flutter/flutter#192177) 2026-09-02 [email protected] [tool] Migrate DoctorCommand to modular dependency injection (flutter/flutter#190758) 2026-09-02 [email protected] Roll Skia from 482b7e285244 to dec311244db4 (3 revisions) (flutter/flutter#192161) 2026-09-02 [email protected] Roll Skia from 28447e9fb8d5 to 482b7e285244 (3 revisions) (flutter/flutter#192157) 2026-09-02 [email protected] feat: Add placeholder to DecorationImage (flutter/flutter#191528) 2026-09-02 [email protected] [Android] Do not schedule engine frames on a detached FlutterJNI (flutter/flutter#191204) 2026-09-02 [email protected] Roll Skia from 3a242fb7cdb3 to 28447e9fb8d5 (1 revision) (flutter/flutter#192145) 2026-09-02 [email protected] Roll Dart SDK from 9164def35347 to d8d7869d8031 (2 revisions) (flutter/flutter#192144) 2026-09-02 [email protected] Add FadeInImageTransition.fadeInOver to fade the image in over the placeholder (flutter/flutter#186246) 2026-09-02 [email protected] Roll Skia from 63d13ec4df6d to 3a242fb7cdb3 (9 revisions) (flutter/flutter#192138) 2026-09-02 [email protected] [flutter_tools] Add --no-plugins flag and disable plugins for benchmark (flutter/flutter#192129) 2026-09-02 [email protected] [tool] Migrate ChannelCommand to modular dependency injection (flutter/flutter#190751) 2026-09-01 [email protected] Add mouseCursor to RawScrollbar (flutter/flutter#185750) 2026-09-01 [email protected] Fix self-comparison and assert typos in TestSemantics (flutter/flutter#191938) 2026-09-01 [email protected] [Linux] Wait for frames to be rendered before using them in another context (flutter/flutter#192094) 2026-09-01 [email protected] [wimp] Turn on multithreading for wimp. (flutter/flutter#191747) 2026-09-01 [email protected] Roll Skia from 3911a1fe7f7a to 63d13ec4df6d (6 revisions) (flutter/flutter#192125) 2026-09-01 [email protected] Remove the redundant flutter/shell/platform/android:robolectric_tests build target (flutter/flutter#192117) 2026-09-01 [email protected] [iOS] Preserve semantics parents after reparenting (flutter/flutter#189686) 2026-09-01 [email protected] [flutter_tools] Report preview reload timing analytics in LspPreviewDetector (flutter/flutter#192120) 2026-09-01 [email protected] [flutter_tools] Implement Templates slice and flutter create integration (flutter/flutter#191748) 2026-09-01 [email protected] Uiscene migrate add2app hosts (flutter/flutter#191847) 2026-09-01 [email protected] Roll Packages from d642322 to 7a7912f (8 revisions) (flutter/flutter#192119) 2026-09-01 [email protected] [web] Anchor flt-semantics-host at 0,0 to fix WebKit semantics offset (flutter/flutter#190486) 2026-09-01 [email protected] 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 [email protected] 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

robert-ancell requested a review from a team as a code owner September 1, 2026 03:26

flutter-dashboard Bot added the CICD Run CI/CD label Sep 1, 2026

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 reviewed Sep 1, 2026

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Comment thread engine/src/flutter/shell/platform/linux/fl_opengl_frame.cc

Comment thread engine/src/flutter/shell/platform/linux/fl_view_renderer_subsurface.cc

robert-ancell mentioned this pull request Sep 1, 2026

[Linux] Use fences to synchronize frames between OpenGL contexts #192098

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mattkae approved these changes Sep 1, 2026

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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 deleted the linux-gl-finish branch September 1, 2026 23:05

This was referenced Sep 2, 2026

Roll Flutter from 0cbd1a4be0a4 to 540a2711c83a (26 revisions) flutter/packages#12723

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Roll Flutter from 0cbd1a4be0a4 to 70797e15325e (27 revisions) flutter/packages#12727

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Axiaobo7788 mentioned this pull request Sep 3, 2026

[Linux][Desktop] Tracking issue for frame pacing and display synchronization gaps affecting animation smoothness #191245

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[Linux] Wait for frames to be rendered before using them in another context - #192094

[Linux] Wait for frames to be rendered before using them in another context#192094
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robert-ancell:linux-gl-finish

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