Update changes as review requested.

Author: scutlight

shell/common/engine.h

@@ -366,8 +366,6 @@ class Engine final : public RuntimeDelegate, PointerDataDispatcher::Delegate {
   //----------------------------------------------------------------------------
   /// @brief      Setup default font manager according to specific platform.
   ///
-  /// @attention  This operation calls `SkFontMgr::RefDefault` which is
-  ///             time-consuming except running at linux and windows.
   void SetupDefaultFontManager();
 
   //----------------------------------------------------------------------------

shell/platform/android/flutter_main.cc

@@ -156,8 +156,9 @@ void FlutterMain::SetupObservatoryUriCallback(JNIEnv* env) {
       });
 }
 
-static void CreateDefaultFontManager(JNIEnv* env, jclass jcaller) {
-  sk_sp<SkFontMgr> font_mgr(SkFontMgr::RefDefault());
+static void PrefetchDefaultFontManager(JNIEnv* env, jclass jcaller) {
+  // Initialize a singleton owned by Skia.
+  SkFontMgr::RefDefault();
 }
 
 bool FlutterMain::Register(JNIEnv* env) {
@@ -169,9 +170,9 @@ bool FlutterMain::Register(JNIEnv* env) {
           .fnPtr = reinterpret_cast<void*>(&Init),
       },
       {
-          .name = "nativeCreateDefaultFontManager",
+          .name = "nativePrefetchDefaultFontManager",
           .signature = "()V",
-          .fnPtr = reinterpret_cast<void*>(&CreateDefaultFontManager),
+          .fnPtr = reinterpret_cast<void*>(&PrefetchDefaultFontManager),
       },
   };
 

shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java

@@ -107,11 +107,11 @@ public static native void nativeInit(
       long initTimeMillis);
 
   /**
-   * Create the default font manager provided by SkFontMgr::RefDefault() which is a process-wide
+   * Prefetch the default font manager provided by SkFontMgr::RefDefault() which is a process-wide
    * singleton owned by Skia. Note that, the first call to SkFontMgr::RefDefault() will take
    * noticeable time, but later calls will return a reference to the preexisting font manager.
    */
-  public static native void nativeCreateDefaultFontManager();
+  public static native void nativePrefetchDefaultFontManager();
 
   // TODO(mattcarroll): add javadocs
   @UiThread

shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java

@@ -144,16 +144,16 @@ public InitResult call() {
 
             System.loadLibrary("flutter");
 
-            // Pre-warm the default font manager as soon as possible on a background thread.
+            // Prefetch the default font manager as soon as possible on a background thread.
             // It helps to reduce time cost of engine setup that blocks the platform thread.
-            new Thread(
+            Executors.newSingleThreadExecutor()
+                .execute(
                     new Runnable() {
                       @Override
                       public void run() {
-                        FlutterJNI.nativeCreateDefaultFontManager();
+                        FlutterJNI.nativePrefetchDefaultFontManager();
                       }
-                    })
-                .start();
+                    });
 
             if (resourceExtractor != null) {
               resourceExtractor.waitForCompletion();