[Impeller] Create a global Vulkan instance in PlaygroundImplVK to prevent SwiftShader from being unloaded after a test completes

impeller/playground/backend/vulkan/playground_impl_vk.cc

@@ -45,6 +45,8 @@ ShaderLibraryMappingsForPlayground() {
   };
 }
 
+vk::UniqueInstance PlaygroundImplVK::global_instance_;
+
 void PlaygroundImplVK::DestroyWindowHandle(WindowHandle handle) {
   if (!handle) {
     return;
@@ -67,6 +69,8 @@ PlaygroundImplVK::PlaygroundImplVK(PlaygroundSwitches switches)
     return;
   }
 
+  InitGlobalVulkanInstance();
+
   ::glfwDefaultWindowHints();
   ::glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
   ::glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
@@ -145,4 +149,33 @@ std::unique_ptr<Surface> PlaygroundImplVK::AcquireSurfaceFrame(
   return surface_context_vk->AcquireNextSurface();
 }
 
+// Create a global instance of Vulkan in order to prevent unloading of the
+// Vulkan library.
+// A test suite may repeatedly create and destroy PlaygroundImplVK instances,
+// and if the PlaygroundImplVK's Vulkan instance is the only one in the
+// process then the Vulkan library will be unloaded when the instance is
+// destroyed.  Repeated loading and unloading of SwiftShader was leaking
+// resources, so this will work around that leak.
+// (see https://github.com/flutter/flutter/issues/138028)
+void PlaygroundImplVK::InitGlobalVulkanInstance() {
+  if (global_instance_) {
+    return;
+  }
+
+  VULKAN_HPP_DEFAULT_DISPATCHER.init(::glfwGetInstanceProcAddress);
+
+  vk::ApplicationInfo application_info;
+  application_info.setApplicationVersion(VK_API_VERSION_1_0);
+  application_info.setApiVersion(VK_API_VERSION_1_1);
+  application_info.setEngineVersion(VK_API_VERSION_1_0);
+  application_info.setPEngineName("PlaygroundImplVK");
+  application_info.setPApplicationName("PlaygroundImplVK");
+
+  auto instance_result =
+      vk::createInstanceUnique(vk::InstanceCreateInfo({}, &application_info));
+  FML_CHECK(instance_result.result == vk::Result::eSuccess)
+      << "Unable to initialize global Vulkan instance";
+  global_instance_ = std::move(instance_result.value);
+}
+
 }  // namespace impeller

impeller/playground/backend/vulkan/playground_impl_vk.h

@@ -24,6 +24,10 @@ class PlaygroundImplVK final : public PlaygroundImpl {
   using UniqueHandle = std::unique_ptr<void, decltype(&DestroyWindowHandle)>;
   UniqueHandle handle_;
 
+  // A global Vulkan instance which ensures that the Vulkan library will remain
+  // loaded throughout the lifetime of the process.
+  static vk::UniqueInstance global_instance_;
+
   // |PlaygroundImpl|
   std::shared_ptr<Context> GetContext() const override;
 
@@ -37,6 +41,8 @@ class PlaygroundImplVK final : public PlaygroundImpl {
   PlaygroundImplVK(const PlaygroundImplVK&) = delete;
 
   PlaygroundImplVK& operator=(const PlaygroundImplVK&) = delete;
+
+  static void InitGlobalVulkanInstance();
 };
 
 }  // namespace impeller