[Impeller] Guard the sampler library caches with a mutex - #193738

…#13220)

Manual roll Flutter from d03768eef055 to 4249ccbc18a3 (158 revisions)

Manual roll requested by [email protected]

flutter/flutter@d03768e...4249ccb

2026-10-12 [email protected] [AGP 9.1.0 Migration #8] Unify add-to-app module wiring on the variant API (flutter/flutter#193717)
2026-10-12 [email protected] [master] Update Flutter DEPS to Dart 5933cb486b4aef2f8cf6b9f89a5651c0d5b0955e (flutter/flutter#193982)
2026-10-12 [email protected] [Android] Fix use-after-free of SurfaceControl.Transaction in HCPP (flutter/flutter#192969)
2026-10-12 [email protected] [windows] Add OpenGL compositor tests against ANGLE at D3D11 feature level 10_0 (flutter/flutter#194114)
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2026-10-12 [email protected] Remove no-shuffle from text_field_test.dart (flutter/flutter#193550)
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2026-10-11 [email protected] Fix another `parameter_assignments` warning (flutter/flutter#193669)
2026-10-11 [email protected] Roll Skia from 3136abef8f58 to 93c9d3ffda25 (1 revision) (flutter/flutter#194169)
2026-10-11 [email protected] [Impeller] Guard the sampler library caches with a mutex (flutter/flutter#193738)
2026-10-11 [email protected] Roll Dart SDK from e9c89888bcc1 to 047ca322aa9c (1 revision) (flutter/flutter#194157)
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2026-10-10 [email protected] Refactored PipelineLibraryGLES (flutter/flutter#193985)
2026-10-09 [email protected] add shorthands for scroll physics subclasses in framework (flutter/flutter#193082)
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2026-10-09 [email protected] Move the Vulkan wrapped-texture helper out of the GPU surface (flutter/flutter#193001)
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2026-10-09 [email protected] Bump dartdoc to 9.0.11 (flutter/flutter#194076)
...

)

`SamplerLibraryMTL`, `SamplerLibraryVK` and `SamplerLibraryGLES` cache
samplers in a plain vector that `GetSampler` scans and then appends to,
with no lock. Flutter GPU calls `GetSampler` on the UI thread
(`RenderPass.bindTexture`) while Impeller calls it on the raster thread
(for example `FramebufferBlendContents::Render`). A scan can read a
buffer that a concurrent `push_back` is reallocating, and two concurrent
inserts can corrupt the vector or drop a sampler that was already
returned.

This PR guards `samplers_` with a mutex in all three backends. On Metal
and Vulkan, the lock covers the lookup and the insert but not sampler
creation, and the insert checks the cache again so concurrent requests
share one sampler. GLES creates no device object, so it holds the lock
for the whole lookup.

The new test, `RendererTest.SamplerLibraryAllowsConcurrentGetSampler`,
starts four threads on a latch, has each request the same 36 samplers,
and checks that every thread gets the same valid sampler for each
descriptor.

Verified on master d03768e: Metal on macOS (M4 Max), and Vulkan
(SwiftShader) and OpenGL ES (Mesa, Xvfb) on Linux x64 with the CI
environment:

| | Without the lock | With the lock |
| --- | --- | --- |
| New test, 40 runs (Metal / Vulkan / GLES) | 0 / 1 / 0 pass | 40/40 on
each |
| New test under TSan | sampler races on all three | no sampler race |
| Repro app from the issue under TSan (Metal) | race in 4 of 6 runs |
none in 6 runs |

The macOS `impeller_unittests` CI filter (2426 passed, 0 failed) and the
Metal backend tests pass, and the format and clang-tidy checks are
clean. On Linux, the full `impeller_unittests` run was stopped early
with 1154 passed and 0 failed, and the runs used the previous revision
of the test, which started its threads with a spin barrier instead of a
latch.

Related: flutter#193721 / flutter#193722 (the same race in `PipelineLibraryMTL`). Both
PRs add a test to `renderer_unittests.cc`; merging them conflicts only
on the `#include <...>` lines.

Fixes flutter#193737

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we expect every widget to implement].
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above.
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`///`).
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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.

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