Reland "Avoid vsync scheduling delay" (flutter#36197)

ci/licenses_golden/licenses_flutter

@@ -1648,6 +1648,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/Platfor
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/SingleViewPresentation.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/util/HandlerCompat.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/PathUtils.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/Preconditions.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/Predicate.java

shell/platform/android/BUILD.gn

@@ -289,6 +289,7 @@ android_java_sources = [
   "io/flutter/plugin/platform/PlatformViewsController.java",
   "io/flutter/plugin/platform/SingleViewPresentation.java",
   "io/flutter/plugin/platform/VirtualDisplayController.java",
+  "io/flutter/util/HandlerCompat.java",
   "io/flutter/util/PathUtils.java",
   "io/flutter/util/Preconditions.java",
   "io/flutter/util/Predicate.java",

shell/platform/android/io/flutter/embedding/engine/dart/PlatformTaskQueue.java

@@ -7,10 +7,13 @@
 import android.os.Handler;
 import android.os.Looper;
 import androidx.annotation.NonNull;
+import io.flutter.util.HandlerCompat;
 
 /** A BinaryMessenger.TaskQueue that posts to the platform thread (aka main thread). */
 public class PlatformTaskQueue implements DartMessenger.DartMessengerTaskQueue {
-  @NonNull private final Handler handler = new Handler(Looper.getMainLooper());
+  // Use an async handler because the default is subject to vsync synchronization and can result
+  // in delays when dispatching tasks.
+  @NonNull private final Handler handler = HandlerCompat.createAsyncHandler(Looper.getMainLooper());
 
   @Override
   public void dispatch(@NonNull Runnable runnable) {

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

@@ -23,6 +23,7 @@
 import io.flutter.FlutterInjector;
 import io.flutter.Log;
 import io.flutter.embedding.engine.FlutterJNI;
+import io.flutter.util.HandlerCompat;
 import io.flutter.util.PathUtils;
 import io.flutter.util.TraceSection;
 import io.flutter.view.VsyncWaiter;
@@ -385,7 +386,7 @@ public void ensureInitializationCompleteAsync(
             Log.e(TAG, "Flutter initialization failed.", e);
             throw new RuntimeException(e);
           }
-          new Handler(Looper.getMainLooper())
+          HandlerCompat.createAsyncHandler(Looper.getMainLooper())
               .post(
                   () -> {
                     ensureInitializationComplete(applicationContext.getApplicationContext(), args);

shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java

@@ -224,19 +224,29 @@ private void setSystemChromeChangeListener() {
         new View.OnSystemUiVisibilityChangeListener() {
           @Override
           public void onSystemUiVisibilityChange(int visibility) {
-            if ((visibility & View.SYSTEM_UI_FLAG_FULLSCREEN) == 0) {
-              // The system bars are visible. Make any desired adjustments to
-              // your UI, such as showing the action bar or other navigational
-              // controls. Another common action is to set a timer to dismiss
-              // the system bars and restore the fullscreen mode that was
-              // previously enabled.
-              platformChannel.systemChromeChanged(false);
-            } else {
-              // The system bars are NOT visible. Make any desired adjustments
-              // to your UI, such as hiding the action bar or other
-              // navigational controls.
-              platformChannel.systemChromeChanged(true);
-            }
+            // `platformChannel.systemChromeChanged` may trigger a callback that eventually results
+            // in a call to `setSystemUiVisibility`.
+            // `setSystemUiVisibility` must not be called in the same frame as when
+            // `onSystemUiVisibilityChange` is received though.
+            //
+            // As such, post `platformChannel.systemChromeChanged` to the view handler to ensure
+            // that downstream callbacks are trigged on the next frame.
+            decorView.post(
+                () -> {
+                  if ((visibility & View.SYSTEM_UI_FLAG_FULLSCREEN) == 0) {
+                    // The system bars are visible. Make any desired adjustments to
+                    // your UI, such as showing the action bar or other navigational
+                    // controls. Another common action is to set a timer to dismiss
+                    // the system bars and restore the fullscreen mode that was
+                    // previously enabled.
+                    platformChannel.systemChromeChanged(false);
+                  } else {
+                    // The system bars are NOT visible. Make any desired adjustments
+                    // to your UI, such as hiding the action bar or other
+                    // navigational controls.
+                    platformChannel.systemChromeChanged(true);
+                  }
+                });
           }
         });
   }

shell/platform/android/io/flutter/util/HandlerCompat.java

@@ -0,0 +1,35 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.util;
+
+import android.os.Build;
+import android.os.Handler;
+import android.os.Looper;
+
+/** Compatability wrapper over {@link Handler}. */
+public final class HandlerCompat {
+  /**
+   * Create a new Handler whose posted messages and runnables are not subject to synchronization
+   * barriers such as display vsync.
+   *
+   * <p>Messages sent to an async handler are guaranteed to be ordered with respect to one another,
+   * but not necessarily with respect to messages from other Handlers. Compatibility behavior:
+   *
+   * <ul>
+   *   <li>SDK 28 and above, this method matches platform behavior.
+   *   <li>Otherwise, returns a synchronous handler instance.
+   * </ul>
+   *
+   * @param looper the Looper that the new Handler should be bound to
+   * @return a new async Handler instance
+   * @see Handler#createAsync(Looper)
+   */
+  public static Handler createAsyncHandler(Looper looper) {
+    if (Build.VERSION.SDK_INT >= 28) {
+      return Handler.createAsync(looper);
+    }
+    return new Handler(looper);
+  }
+}

shell/platform/android/test/io/flutter/plugin/platform/PlatformPluginTest.java

@@ -6,6 +6,7 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.anyBoolean;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.spy;
@@ -27,7 +28,6 @@
 import androidx.activity.OnBackPressedCallback;
 import androidx.fragment.app.FragmentActivity;
 import androidx.test.core.app.ApplicationProvider;
-import androidx.test.ext.junit.runners.AndroidJUnit4;
 import io.flutter.embedding.engine.systemchannels.PlatformChannel;
 import io.flutter.embedding.engine.systemchannels.PlatformChannel.Brightness;
 import io.flutter.embedding.engine.systemchannels.PlatformChannel.ClipboardContentFormat;
@@ -38,10 +38,13 @@
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.robolectric.Robolectric;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.android.controller.ActivityController;
 import org.robolectric.annotation.Config;
+import org.robolectric.shadows.ShadowLooper;
 
 @Config(manifest = Config.NONE)
-@RunWith(AndroidJUnit4.class)
+@RunWith(RobolectricTestRunner.class)
 public class PlatformPluginTest {
   private final Context ctx = ApplicationProvider.getApplicationContext();
 
@@ -368,6 +371,32 @@ public void setSystemUiMode() {
     }
   }
 
+  @Test
+  public void setSystemUiModeListener() {
+    ActivityController<Activity> controller = Robolectric.buildActivity(Activity.class);
+    controller.setup();
+    Activity fakeActivity = controller.get();
+
+    PlatformChannel fakePlatformChannel = mock(PlatformChannel.class);
+    PlatformPlugin platformPlugin = new PlatformPlugin(fakeActivity, fakePlatformChannel);
+
+    // Subscribe to system Ui visibility events.
+    platformPlugin.mPlatformMessageHandler.setSystemUiChangeListener();
+
+    // Simulate changing of the system ui visibility.
+    fakeActivity.getWindow().getDecorView().dispatchSystemUiVisibilityChanged(0);
+
+    // No events should have been sent to the platform channel yet. They are scheduled for
+    // the next frame.
+    verify(fakePlatformChannel, never()).systemChromeChanged(anyBoolean());
+
+    // Simulate the next frame.
+    ShadowLooper.runUiThreadTasksIncludingDelayedTasks();
+
+    // Now the platform channel should receive the event.
+    verify(fakePlatformChannel).systemChromeChanged(anyBoolean());
+  }
+
   @Config(sdk = 28)
   @Test
   public void doNotEnableEdgeToEdgeOnOlderSdk() {

shell/platform/android/test/io/flutter/util/HandlerCompatTest.java

@@ -0,0 +1,29 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.util;
+
+import static org.junit.Assert.assertTrue;
+
+import android.os.Handler;
+import android.os.Looper;
+import android.os.Message;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+@RunWith(RobolectricTestRunner.class)
+public class HandlerCompatTest {
+  @Test
+  @Config(sdk = 28)
+  public void createAsync_createsAnAsyncHandler() {
+    Handler handler = Handler.createAsync(Looper.getMainLooper());
+
+    Message message = Message.obtain();
+    handler.sendMessageAtTime(message, 0);
+
+    assertTrue(message.isAsynchronous());
+  }
+}

tools/android_lint/project.xml

@@ -23,6 +23,7 @@
     <src file="../../../flutter/shell/platform/android/io/flutter/util/Predicate.java" />
     <src file="../../../flutter/shell/platform/android/io/flutter/util/TraceSection.java" />
     <src file="../../../flutter/shell/platform/android/io/flutter/util/PathUtils.java" />
+    <src file="../../../flutter/shell/platform/android/io/flutter/util/HandlerCompat.java" />
     <src file="../../../flutter/shell/platform/android/io/flutter/embedding/android/KeyboardMap.java" />
     <src file="../../../flutter/shell/platform/android/io/flutter/embedding/android/KeyboardManager.java" />
     <src file="../../../flutter/shell/platform/android/io/flutter/embedding/android/AndroidTouchProcessor.java" />