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

Libcxx is leaking a thread-local storage key each time SwiftShader is loaded
and unloaded.  If a test's Vulkan instance is the only one in the process,
then SwiftShader will be unloaded after the test ends.  If many Vulkan
playground tests run in a suite, then eventually the leak will cause the
process to exceed its limit of TLS keys and the suite will fail.

The process can ensure that SwiftShader remains loaded by holding another
Vulkan instance that persists across all tests in the suite.

Fixes flutter/flutter#138028

Author: jason-simmons

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