Load FlutterLoader when creating FlutterEngineGroup (#23980)

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

@@ -8,7 +8,9 @@ import android.content.Context;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
+import io.flutter.FlutterInjector;
 import io.flutter.embedding.engine.dart.DartExecutor.DartEntrypoint;
+import io.flutter.embedding.engine.loader.FlutterLoader;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -25,6 +27,9 @@ import java.util.List;
  * io.flutter.embedding.engine.FlutterEngine}s are created, resources from an existing living {@link
  * io.flutter.embedding.engine.FlutterEngine} is re-used.
  *
+ * <p>The shared resources are kept until the last surviving {@link
+ * io.flutter.embedding.engine.FlutterEngine} is destroyed.
+ *
  * <p>Deleting a FlutterEngineGroup doesn't invalidate its existing {@link
  * io.flutter.embedding.engine.FlutterEngine}s, but it eliminates the possibility to create more
  * {@link io.flutter.embedding.engine.FlutterEngine}s in that group.
@@ -33,6 +38,23 @@ public class FlutterEngineGroup {
 
   /* package */ @VisibleForTesting final List<FlutterEngine> activeEngines = new ArrayList<>();
 
+  /** Create a FlutterEngineGroup whose child engines will share resources. */
+  public FlutterEngineGroup(@NonNull Context context) {
+    this(context, null);
+  }
+
+  /**
+   * Create a FlutterEngineGroup whose child engines will share resources. Use {@code dartVmArgs} to
+   * pass flags to the Dart VM during initialization.
+   */
+  public FlutterEngineGroup(@NonNull Context context, @Nullable String[] dartVmArgs) {
+    FlutterLoader loader = FlutterInjector.instance().flutterLoader();
+    if (!loader.initialized()) {
+      loader.startInitialization(context.getApplicationContext());
+      loader.ensureInitializationComplete(context, dartVmArgs);
+    }
+  }
+
   /**
    * Creates a {@link io.flutter.embedding.engine.FlutterEngine} in this group and run its {@link
    * io.flutter.embedding.engine.dart.DartExecutor} with a default entrypoint of the "main" function
@@ -67,18 +89,13 @@ public class FlutterEngineGroup {
   public FlutterEngine createAndRunEngine(
       @NonNull Context context, @Nullable DartEntrypoint dartEntrypoint) {
     FlutterEngine engine = null;
-    // This is done up here because an engine needs to be created first in order to be able to use
-    // DartEntrypoint.createDefault. The engine creation initializes the FlutterLoader so
-    // DartEntrypoint known where to find the assets for the AOT or kernel code.
-    if (activeEngines.size() == 0) {
-      engine = createEngine(context);
-    }
 
     if (dartEntrypoint == null) {
       dartEntrypoint = DartEntrypoint.createDefault();
     }
 
     if (activeEngines.size() == 0) {
+      engine = createEngine(context);
       engine.getDartExecutor().executeDartEntrypoint(dartEntrypoint);
     } else {
       engine = activeEngines.get(0).spawn(context, dartEntrypoint);

shell/platform/android/test/io/flutter/embedding/engine/FlutterEngineGroupComponentTest.java

@@ -8,12 +8,17 @@ import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.eq;
+import static org.mockito.Mockito.isNull;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import android.content.Context;
-import io.flutter.embedding.engine.dart.DartExecutor;
+import android.content.res.AssetManager;
+import io.flutter.FlutterInjector;
 import io.flutter.embedding.engine.dart.DartExecutor.DartEntrypoint;
 import io.flutter.embedding.engine.loader.FlutterLoader;
 import io.flutter.plugins.GeneratedPluginRegistrant;
@@ -27,34 +32,41 @@ import org.robolectric.RobolectricTestRunner;
 import org.robolectric.RuntimeEnvironment;
 import org.robolectric.annotation.Config;
 
-// It's a component test because it tests both FlutterEngineGroup and FlutterEngine.
+// It's a component test because it tests the FlutterEngineGroup its components such as the
+// FlutterEngine and the DartExecutor.
 @Config(manifest = Config.NONE)
 @RunWith(RobolectricTestRunner.class)
 public class FlutterEngineGroupComponentTest {
-  @Mock FlutterJNI flutterJNI;
+  @Mock FlutterJNI mockflutterJNI;
+  @Mock FlutterLoader mockFlutterLoader;
   FlutterEngineGroup engineGroupUnderTest;
   FlutterEngine firstEngineUnderTest;
   boolean jniAttached;
 
   @Before
   public void setUp() {
+    FlutterInjector.reset();
+
     MockitoAnnotations.initMocks(this);
     jniAttached = false;
-    when(flutterJNI.isAttached()).thenAnswer(invocation -> jniAttached);
-    doAnswer(invocation -> jniAttached = true).when(flutterJNI).attachToNative(false);
+    when(mockflutterJNI.isAttached()).thenAnswer(invocation -> jniAttached);
+    doAnswer(invocation -> jniAttached = true).when(mockflutterJNI).attachToNative(false);
     GeneratedPluginRegistrant.clearRegisteredEngines();
 
+    when(mockFlutterLoader.findAppBundlePath()).thenReturn("some/path/to/flutter_assets");
+    FlutterInjector.setInstance(
+        new FlutterInjector.Builder().setFlutterLoader(mockFlutterLoader).build());
+
     firstEngineUnderTest =
         spy(
             new FlutterEngine(
                 RuntimeEnvironment.application,
                 mock(FlutterLoader.class),
-                flutterJNI,
+                mockflutterJNI,
                 /*dartVmArgs=*/ new String[] {},
                 /*automaticallyRegisterPlugins=*/ false));
-    when(firstEngineUnderTest.getDartExecutor()).thenReturn(mock(DartExecutor.class));
     engineGroupUnderTest =
-        new FlutterEngineGroup() {
+        new FlutterEngineGroup(RuntimeEnvironment.application) {
           @Override
           FlutterEngine createEngine(Context context) {
             return firstEngineUnderTest;
@@ -127,4 +139,21 @@ public class FlutterEngineGroupComponentTest {
             RuntimeEnvironment.application, mock(DartEntrypoint.class));
     assertEquals(2, engineGroupUnderTest.activeEngines.size());
   }
+
+  @Test
+  public void canCreateAndRunCustomEntrypoints() {
+    FlutterEngine firstEngine =
+        engineGroupUnderTest.createAndRunEngine(
+            RuntimeEnvironment.application,
+            new DartEntrypoint(
+                FlutterInjector.instance().flutterLoader().findAppBundlePath(),
+                "other entrypoint"));
+    assertEquals(1, engineGroupUnderTest.activeEngines.size());
+    verify(mockflutterJNI, times(1))
+        .runBundleAndSnapshotFromLibrary(
+            eq("some/path/to/flutter_assets"),
+            eq("other entrypoint"),
+            isNull(String.class),
+            any(AssetManager.class));
+  }
 }

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

@@ -14,7 +14,7 @@ public class SpawnedEngineActivity extends TestActivity {
 
   @Override
   public FlutterEngine provideFlutterEngine(@NonNull Context context) {
-    FlutterEngineGroup engineGroup = new FlutterEngineGroup();
+    FlutterEngineGroup engineGroup = new FlutterEngineGroup(context);
     engineGroup.createAndRunDefaultEngine(context);
 
     FlutterEngine secondEngine = engineGroup.createAndRunDefaultEngine(context);