Fix ensureInitializationCompleteAsync callback when already initialized. (#39675)

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

@@ -234,6 +234,7 @@ public void ensureInitializationCompleteAsync(
           "ensureInitializationComplete must be called after startInitialization");
     }
     if (initialized) {
+      callbackHandler.post(callback);
       return;
     }
     new Thread(

testing/scenario_app/android/app/src/main/java/dev/flutter/scenarios/TextPlatformViewActivity.java

@@ -1,22 +1,26 @@
 package dev.flutter.scenarios;
 
 import android.Manifest;
+import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 import android.support.annotation.NonNull;
 import io.flutter.Log;
 import io.flutter.embedding.android.FlutterActivity;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterShellArgs;
+import io.flutter.embedding.engine.loader.FlutterLoader;
 import io.flutter.plugin.common.BasicMessageChannel;
 import io.flutter.plugin.common.BinaryCodec;
 import java.io.FileDescriptor;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 public class TextPlatformViewActivity extends FlutterActivity {
   static final String TAG = "Scenarios";
@@ -31,7 +35,19 @@ protected void onCreate(Bundle savedInstanceState) {
       }
       // Run for one minute, get the timeline data, write it, and finish.
       final Uri logFileUri = launchIntent.getData();
-      new Handler().postDelayed(() -> writeTimelineData(logFileUri), 20000);
+      new Handler()
+          .postDelayed(
+              new Runnable() {
+                @Override
+                public void run() {
+                  writeTimelineData(logFileUri);
+
+                  testFlutterLoaderCallbackWhenInitializedTwice();
+                }
+              },
+              20000);
+    } else {
+      testFlutterLoaderCallbackWhenInitializedTwice();
     }
   }
 
@@ -80,4 +96,46 @@ private void writeTimelineData(Uri logFile) {
           finish();
         });
   }
+
+  /**
+   * This method verifies that {@link FlutterLoader#ensureInitializationCompleteAsync(Context,
+   * String[], Handler, Runnable)} invokes its callback when called after initialization.
+   */
+  private void testFlutterLoaderCallbackWhenInitializedTwice() {
+    FlutterLoader flutterLoader = new FlutterLoader();
+
+    // Flutter is probably already loaded in this app based on
+    // code that ran before this method. Nonetheless, invoke the
+    // blocking initialization here to ensure it's initialized.
+    flutterLoader.startInitialization(getApplicationContext());
+    flutterLoader.ensureInitializationComplete(getApplication(), new String[] {});
+
+    // Now that Flutter is loaded, invoke ensureInitializationCompleteAsync with
+    // a callback and verify that the callback is invoked.
+    Handler mainHandler = new Handler(Looper.getMainLooper());
+
+    final AtomicBoolean didInvokeCallback = new AtomicBoolean(false);
+
+    flutterLoader.ensureInitializationCompleteAsync(
+        getApplication(),
+        new String[] {},
+        mainHandler,
+        new Runnable() {
+          @Override
+          public void run() {
+            didInvokeCallback.set(true);
+          }
+        });
+
+    mainHandler.post(
+        new Runnable() {
+          @Override
+          public void run() {
+            if (!didInvokeCallback.get()) {
+              throw new RuntimeException(
+                  "Failed test: FlutterLoader#ensureInitializationCompleteAsync() did not invoke its callback.");
+            }
+          }
+        });
+  }
 }