[Impeller] Add render target cache clearing and test hook by andywolff · Pull Request #193497 · flutter/flutter

andywolff · 2026-09-29T06:55:46Z

Fixes #193015
Part of #192992

During testing, RenderTargetCache retained allocated offscreen render targets across consecutive test cases within the same process. When earlier tests performed offscreen drawing or backdrop filtering passes, dirty textures remained in the cache and were recycled into subsequent test passes, leading to test order flakiness and non-deterministic golden snapshots (#192992).

To address both production memory pressure handling (#193015) and test isolation, I added cache clearing methods across the Impeller rendering pipeline. In the engine, RenderTargetAllocator and RenderTargetCache now provide a Clear() method that drops all cached texture allocations. I wired this cleanup through ContentContext, AiksContext, Rasterizer, Engine, and Shell.

In production, the rasterizer now purges the render target cache when receiving low-memory warning signals (FlutterEngineNotifyLowMemoryWarning / Rasterizer::NotifyLowMemoryWarning).

For tests, I exposed a general PlatformDispatcher.resetInternalState() hook through native platform configuration bindings. This mirrors ServicesBinding.resetInternalState() and will allow test harnesses to purge cached offscreen render targets between tests to prevent texture leakage across test boundaries while keeping the engine test interface extensible. To prevent merge queue and postsubmit analyzer failures against the baseline prebuilt sky_engine, the framework test wiring (TestWidgetsFlutterBinding.postTest and TestPlatformDispatcher.resetInternalState()) is deferred to a follow-up PR once this engine commit rolls.

I also added C++ unit tests in RasterizerTest, ShellTest, EngineTest, and RuntimeControllerTest.

Pre-launch Checklist

gemini-code-assist

Code Review

This pull request introduces a mechanism to clear cached render targets and textures maintained by the rasterizer. It adds clearRenderTargetCache to PlatformDispatcher along with its native bindings and engine-side implementations across Shell, Engine, Rasterizer, AiksContext, and ContentContext. Additionally, it integrates this clearing mechanism into TestWidgetsFlutterBinding.resetInternalState to ensure test isolation and includes corresponding unit tests. There are no review comments, and I have no feedback to provide.

loic-sharma

Dart + core engine looks good to me. However, I'm not familiar with Impeller so please also get an approval from someone who is :)

gaaclarke

Looking good, just want more clear assertions in the tests.

gaaclarke · 2026-10-01T22:09:18Z

+  EXPECT_CALL(*surface, GetAiksContext()).WillRepeatedly(Return(aiks_context));
+  EXPECT_CALL(*surface, MakeRenderContextCurrent()).WillRepeatedly([] {
+    return std::make_unique<GLContextDefaultResult>(true);
+  });


Where is the assertion that the caches are cleared?

This test isn't really doing anything useful without that, huh? Thanks for catching. Updated the header and added an EXPECT_CALL, then confirmed that this (and the tests from your other comments) fail when the clear is commented out

gaaclarke · 2026-10-01T22:09:38Z

+  auto aiks_context = std::make_shared<impeller::AiksContext>(nullptr, nullptr);
+  EXPECT_CALL(*surface, GetAiksContext()).WillRepeatedly(Return(aiks_context));
+  EXPECT_CALL(*surface, MakeRenderContextCurrent()).WillRepeatedly([] {
+    return std::make_unique<GLContextDefaultResult>(true);
+  });


gaaclarke · 2026-10-01T22:11:16Z

+  test('TestPlatformDispatcher delegates resetInternalState', () {
+    final testPlatformDispatcher = TestPlatformDispatcher(
+      platformDispatcher: PlatformDispatcher.instance,
+    );
+    testPlatformDispatcher.resetInternalState();
+  });


there's no assertion here either

Fixed and red-green validated

auto-submit · 2026-10-05T20:04:31Z

autosubmit label was removed for flutter/flutter/193497, because - The status or check suite Dashboard Checks has failed. Please fix the issues identified (or deflake) before re-applying this label.

…er#193842) Part of flutter#192992 Follow-up to flutter#193497. In flutter#193497, I introduced `PlatformDispatcher.resetInternalState()` to allow test harnesses to purge internal engine caches (such as Impeller's offscreen `RenderTargetCache`) between test cases to ensure test isolation. Now that the engine changes have rolled into the framework, this PR connects the framework test harness: 1. Implements `TestPlatformDispatcher.resetInternalState()` in `packages/flutter_test/lib/src/window.dart` to delegate to the underlying `PlatformDispatcher`. 2. Invokes `platformDispatcher.resetInternalState()` in `TestWidgetsFlutterBinding.postTest` alongside `ServicesBinding.instance.resetInternalState()`. 3. Adds a unit test in `packages/flutter_test/test/platform_dispatcher_test.dart` to verify delegation. ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant in-code documentation (doc comments with `///`). - [x] If this PR introduces a new feature or capability, I created and linked a website documentation issue or PR in [flutter/website] (or verified none is needed). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing.  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [flutter/website]: https://github.com/flutter/website [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

@andywolff

…3497) Fixes flutter#193015 Part of flutter#192992 During testing, `RenderTargetCache` retained allocated offscreen render targets across consecutive test cases within the same process. When earlier tests performed offscreen drawing or backdrop filtering passes, dirty textures remained in the cache and were recycled into subsequent test passes, leading to test order flakiness and non-deterministic golden snapshots (flutter#192992). To address both production memory pressure handling (flutter#193015) and test isolation, I added cache clearing methods across the Impeller rendering pipeline. In the engine, `RenderTargetAllocator` and `RenderTargetCache` now provide a `Clear()` method that drops all cached texture allocations. I wired this cleanup through `ContentContext`, `AiksContext`, `Rasterizer`, `Engine`, and `Shell`. In production, the rasterizer now purges the render target cache when receiving low-memory warning signals (`FlutterEngineNotifyLowMemoryWarning` / `Rasterizer::NotifyLowMemoryWarning`). For tests, I exposed a general `PlatformDispatcher.resetInternalState()` hook through native platform configuration bindings. This mirrors `ServicesBinding.resetInternalState()` and will allow test harnesses to purge cached offscreen render targets between tests to prevent texture leakage across test boundaries while keeping the engine test interface extensible. To prevent merge queue and postsubmit analyzer failures against the baseline prebuilt `sky_engine`, the framework test wiring (`TestWidgetsFlutterBinding.postTest` and `TestPlatformDispatcher.resetInternalState()`) is deferred to a follow-up PR once this engine commit rolls. I also added C++ unit tests in `RasterizerTest`, `ShellTest`, `EngineTest`, and `RuntimeControllerTest`. ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant in-code documentation (doc comments with `///`). - [x] If this PR introduces a new feature or capability, I created and linked a website documentation issue or PR in [flutter/website] (or verified none is needed). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing.  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [flutter/website]: https://github.com/flutter/website [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

…er#193842) Part of flutter#192992 Follow-up to flutter#193497. In flutter#193497, I introduced `PlatformDispatcher.resetInternalState()` to allow test harnesses to purge internal engine caches (such as Impeller's offscreen `RenderTargetCache`) between test cases to ensure test isolation. Now that the engine changes have rolled into the framework, this PR connects the framework test harness: 1. Implements `TestPlatformDispatcher.resetInternalState()` in `packages/flutter_test/lib/src/window.dart` to delegate to the underlying `PlatformDispatcher`. 2. Invokes `platformDispatcher.resetInternalState()` in `TestWidgetsFlutterBinding.postTest` alongside `ServicesBinding.instance.resetInternalState()`. 3. Adds a unit test in `packages/flutter_test/test/platform_dispatcher_test.dart` to verify delegation. ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant in-code documentation (doc comments with `///`). - [x] If this PR introduces a new feature or capability, I created and linked a website documentation issue or PR in [flutter/website] (or verified none is needed). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing.  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [flutter/website]: https://github.com/flutter/website [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

@andywolff

andywolff added the CICD Run CI/CD label Sep 29, 2026

andywolff force-pushed the test_randomization branch 6 times, most recently from f7cc179 to 89615d5 Compare September 30, 2026 05:45

[Impeller] Add render target cache clearing and test hook

b3dabb0

andywolff force-pushed the test_randomization branch from 89615d5 to b3dabb0 Compare September 30, 2026 06:52

andywolff marked this pull request as ready for review September 30, 2026 16:33

gemini-code-assist Bot reviewed Sep 30, 2026

View reviewed changes

andywolff requested a review from gaaclarke September 30, 2026 16:51

loic-sharma self-requested a review September 30, 2026 17:40

Document clearRenderTargetCache usage constraints

42482d9