[Impeller] Delete command pools held by the CommandPoolRecyclerVK after decoding an image on the IO thread (flutter/engine#55398)

In the Vulkan backend, the CommandPoolRecyclerVK stores command pools that can be reused while rendering a frame.  For each frame, SurfaceContextVK::AcquireNextSurface calls CommandPoolRecyclerVK::Dispose to clear the cached pools.

However, the CommandPoolRecyclerVK's cache of pools is placed in thread-local storage.  So command pools used on the IO thread will not be cleaned up if frame rendering calls Dispose on the raster thread.

This PR adds a Context API that the IO thread can call after using a command pool in order to ensure that cached resources are disposed.

Fixes https://github.com/flutter/flutter/issues/155519

engine/src/flutter/impeller/renderer/backend/vulkan/context_vk.cc

@@ -608,6 +608,10 @@ void ContextVK::InitializeCommonlyUsedShadersIfNeeded() const {
   auto pass = builder.Build(GetDevice());
 }
 
+void ContextVK::DisposeThreadLocalCachedResources() {
+  command_pool_recycler_->Dispose();
+}
+
 const std::shared_ptr<YUVConversionLibraryVK>&
 ContextVK::GetYUVConversionLibrary() const {
   return yuv_conversion_library_;

engine/src/flutter/impeller/renderer/backend/vulkan/context_vk.h

@@ -167,8 +167,12 @@ class ContextVK final : public Context,
 
   void RecordFrameEndTime() const;
 
+  // |Context|
   void InitializeCommonlyUsedShadersIfNeeded() const override;
 
+  // |Context|
+  void DisposeThreadLocalCachedResources() override;
+
   /// @brief Whether the Android Surface control based swapchain should be
   /// disabled, even if the device is capable of supporting it.
   bool GetShouldDisableSurfaceControlSwapchain() const;

engine/src/flutter/impeller/renderer/backend/vulkan/context_vk_unittests.cc

@@ -72,6 +72,25 @@ TEST(ContextVKTest, DeletesCommandPoolsOnAllThreads) {
   ASSERT_FALSE(weak_pool_thread.lock());
 }
 
+TEST(ContextVKTest, ThreadLocalCleanupDeletesCommandPool) {
+  std::shared_ptr<ContextVK> context = MockVulkanContextBuilder().Build();
+
+  fml::AutoResetWaitableEvent latch1, latch2;
+  std::weak_ptr<CommandPoolVK> weak_pool;
+  std::thread thread([&]() {
+    weak_pool = context->GetCommandPoolRecycler()->Get();
+    context->DisposeThreadLocalCachedResources();
+    latch1.Signal();
+    latch2.Wait();
+  });
+
+  latch1.Wait();
+  ASSERT_FALSE(weak_pool.lock());
+
+  latch2.Signal();
+  thread.join();
+}
+
 TEST(ContextVKTest, DeletePipelineAfterContext) {
   std::shared_ptr<Pipeline<PipelineDescriptor>> pipeline;
   std::shared_ptr<std::vector<std::string>> functions;

engine/src/flutter/impeller/renderer/backend/vulkan/surface_context_vk.cc

@@ -103,6 +103,10 @@ void SurfaceContextVK::InitializeCommonlyUsedShadersIfNeeded() const {
   parent_->InitializeCommonlyUsedShadersIfNeeded();
 }
 
+void SurfaceContextVK::DisposeThreadLocalCachedResources() {
+  parent_->DisposeThreadLocalCachedResources();
+}
+
 const std::shared_ptr<ContextVK>& SurfaceContextVK::GetParent() const {
   return parent_;
 }

engine/src/flutter/impeller/renderer/backend/vulkan/surface_context_vk.h

@@ -80,8 +80,12 @@ class SurfaceContextVK : public Context,
   ///        recreated on the next frame.
   void UpdateSurfaceSize(const ISize& size) const;
 
+  // |Context|
   void InitializeCommonlyUsedShadersIfNeeded() const override;
 
+  // |Context|
+  void DisposeThreadLocalCachedResources() override;
+
   const vk::Device& GetDevice() const;
 
   const std::shared_ptr<ContextVK>& GetParent() const;

engine/src/flutter/impeller/renderer/context.h

@@ -196,6 +196,13 @@ class Context {
   /// shader variants, as well as forcing driver initialization.
   virtual void InitializeCommonlyUsedShadersIfNeeded() const {}
 
+  /// Dispose resources that are cached on behalf of the current thread.
+  ///
+  /// Some backends such as Vulkan may cache resources that can be reused while
+  /// executing a rendering operation.  This API can be called after the
+  /// operation completes in order to clear the cache.
+  virtual void DisposeThreadLocalCachedResources() {}
+
  protected:
   Context();
 

engine/src/flutter/lib/ui/painting/image_decoder_impeller.cc

@@ -382,6 +382,8 @@ ImageDecoderImpeller::UnsafeUploadTextureToPrivate(
     return std::make_pair(nullptr, decode_error);
   }
 
+  context->DisposeThreadLocalCachedResources();
+
   return std::make_pair(
       impeller::DlImageImpeller::Make(std::move(result_texture)),
       std::string());

engine/src/flutter/lib/ui/painting/image_encoding_impeller.cc

@@ -188,6 +188,8 @@ void ImageEncodingImpeller::ConvertDlImageToSkImage(
            .ok()) {
     FML_LOG(ERROR) << "Failed to submit commands.";
   }
+
+  impeller_context->DisposeThreadLocalCachedResources();
 }
 
 void ImageEncodingImpeller::ConvertImageToRaster(