Create feature flag to make estimation for remaining time in frame for view preallocation more precise

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountItemDispatcher.java

@@ -21,6 +21,7 @@
 import com.facebook.react.bridge.ReactNoCrashSoftException;
 import com.facebook.react.bridge.ReactSoftExceptionLogger;
 import com.facebook.react.bridge.RetryableMountingLayerException;
+import com.facebook.react.bridge.UiThreadUtil;
 import com.facebook.react.fabric.mounting.mountitems.DispatchCommandMountItem;
 import com.facebook.react.fabric.mounting.mountitems.MountItem;
 import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags;
@@ -54,6 +55,21 @@ public class MountItemDispatcher {
   private long mBatchedExecutionTime = 0L;
   private long mRunStartTime = 0L;
 
+  private long mLastFrameTimeNanos = 0L;
+  private boolean mIsPremountScheduled = false;
+  private final Runnable mPremountRunnable =
+      () -> {
+        mIsPremountScheduled = false;
+
+        if (mPreMountItems.isEmpty()) {
+          // Avoid starting systrace if there are no pre mount items.
+          return;
+        }
+
+        long deadline = mLastFrameTimeNanos + (FRAME_TIME_NS / 2);
+        dispatchPreMountItemsImpl(deadline);
+      };
+
   public MountItemDispatcher(MountingManager mountingManager, ItemDispatchListener listener) {
     mMountingManager = mountingManager;
     mItemDispatchListener = listener;
@@ -338,22 +354,35 @@ private boolean dispatchMountItems() {
   @UiThread
   @ThreadConfined(UI)
   public void dispatchPreMountItems(long frameTimeNanos) {
+    mLastFrameTimeNanos = frameTimeNanos;
+
     if (mPreMountItems.isEmpty()) {
       // Avoid starting systrace if there are no pre mount items.
       return;
     }
 
+    if (ReactNativeFeatureFlags.enablePreciseSchedulingForPremountItemsOnAndroid()) {
+      if (!mIsPremountScheduled) {
+        mIsPremountScheduled = true;
+        UiThreadUtil.getUiThreadHandler().post(mPremountRunnable);
+      }
+    } else {
+      long deadline = mLastFrameTimeNanos + FRAME_TIME_NS / 2;
+      dispatchPreMountItemsImpl(deadline);
+    }
+  }
+
+  private void dispatchPreMountItemsImpl(long deadline) {
     Systrace.beginSection(
         Systrace.TRACE_TAG_REACT_JAVA_BRIDGE, "MountItemDispatcher::premountViews");
 
     // dispatchPreMountItems cannot be reentrant, but we want to prevent dispatchMountItems from
     // reentering during dispatchPreMountItems
     mInDispatch = true;
 
-    long frameTimeDeadline = frameTimeNanos + FRAME_TIME_NS / 2;
     try {
       while (true) {
-        if (System.nanoTime() > frameTimeDeadline) {
+        if (System.nanoTime() > deadline) {
           break;
         }
 

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlags.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<60fcb02736ca814a842225291e3a55b1>>
+ * @generated SignedSource<<73409b567e77f17838ae9681a8e20be6>>
  */
 
 /**
@@ -148,6 +148,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun enableMicrotasks(): Boolean = accessor.enableMicrotasks()
 
+  /**
+   * Moves execution of pre-mount items to outside the choregrapher in the main thread, so we can estimate idle time more precisely (Android only).
+   */
+  @JvmStatic
+  public fun enablePreciseSchedulingForPremountItemsOnAndroid(): Boolean = accessor.enablePreciseSchedulingForPremountItemsOnAndroid()
+
   /**
    * When enabled, Android will receive prop updates based on the differences between the last rendered shadow node and the last committed shadow node.
    */

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<f2a64fef9775f1890adcf3d761061182>>
+ * @generated SignedSource<<9f2978b5a732a3ca4f3c3d74debba782>>
  */
 
 /**
@@ -40,6 +40,7 @@ public class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAccesso
   private var enableLayoutAnimationsOnIOSCache: Boolean? = null
   private var enableLongTaskAPICache: Boolean? = null
   private var enableMicrotasksCache: Boolean? = null
+  private var enablePreciseSchedulingForPremountItemsOnAndroidCache: Boolean? = null
   private var enablePropsUpdateReconciliationAndroidCache: Boolean? = null
   private var enableReportEventPaintTimeCache: Boolean? = null
   private var enableSynchronousStateUpdatesCache: Boolean? = null
@@ -251,6 +252,15 @@ public class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAccesso
     return cached
   }
 
+  override fun enablePreciseSchedulingForPremountItemsOnAndroid(): Boolean {
+    var cached = enablePreciseSchedulingForPremountItemsOnAndroidCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.enablePreciseSchedulingForPremountItemsOnAndroid()
+      enablePreciseSchedulingForPremountItemsOnAndroidCache = cached
+    }
+    return cached
+  }
+
   override fun enablePropsUpdateReconciliationAndroid(): Boolean {
     var cached = enablePropsUpdateReconciliationAndroidCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxInterop.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<03618f182004add50655a88e6e65e96d>>
+ * @generated SignedSource<<0d2f5427661ce67e468aea47bdd29802>>
  */
 
 /**
@@ -68,6 +68,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun enableMicrotasks(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun enablePreciseSchedulingForPremountItemsOnAndroid(): Boolean
+
   @DoNotStrip @JvmStatic public external fun enablePropsUpdateReconciliationAndroid(): Boolean
 
   @DoNotStrip @JvmStatic public external fun enableReportEventPaintTime(): Boolean

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<fc795741e932cf24e5bfb7e2fe1046ae>>
+ * @generated SignedSource<<72e3e7b5a53e64f8f48310d8b07cdf76>>
  */
 
 /**
@@ -63,6 +63,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun enableMicrotasks(): Boolean = false
 
+  override fun enablePreciseSchedulingForPremountItemsOnAndroid(): Boolean = false
+
   override fun enablePropsUpdateReconciliationAndroid(): Boolean = false
 
   override fun enableReportEventPaintTime(): Boolean = false

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsLocalAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<0dbb1f1a08649132955698ac51050e62>>
+ * @generated SignedSource<<e1a44f8e54709e70934f1d418d4ed80f>>
  */
 
 /**
@@ -44,6 +44,7 @@ public class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcces
   private var enableLayoutAnimationsOnIOSCache: Boolean? = null
   private var enableLongTaskAPICache: Boolean? = null
   private var enableMicrotasksCache: Boolean? = null
+  private var enablePreciseSchedulingForPremountItemsOnAndroidCache: Boolean? = null
   private var enablePropsUpdateReconciliationAndroidCache: Boolean? = null
   private var enableReportEventPaintTimeCache: Boolean? = null
   private var enableSynchronousStateUpdatesCache: Boolean? = null
@@ -275,6 +276,16 @@ public class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun enablePreciseSchedulingForPremountItemsOnAndroid(): Boolean {
+    var cached = enablePreciseSchedulingForPremountItemsOnAndroidCache
+    if (cached == null) {
+      cached = currentProvider.enablePreciseSchedulingForPremountItemsOnAndroid()
+      accessedFeatureFlags.add("enablePreciseSchedulingForPremountItemsOnAndroid")
+      enablePreciseSchedulingForPremountItemsOnAndroidCache = cached
+    }
+    return cached
+  }
+
   override fun enablePropsUpdateReconciliationAndroid(): Boolean {
     var cached = enablePropsUpdateReconciliationAndroidCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsProvider.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<79cd9812257f42d553b49a3f6d3d4989>>
+ * @generated SignedSource<<0f6129ccbcf7857785724f14b41edb2d>>
  */
 
 /**
@@ -63,6 +63,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun enableMicrotasks(): Boolean
 
+  @DoNotStrip public fun enablePreciseSchedulingForPremountItemsOnAndroid(): Boolean
+
   @DoNotStrip public fun enablePropsUpdateReconciliationAndroid(): Boolean
 
   @DoNotStrip public fun enableReportEventPaintTime(): Boolean

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.cpp

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<9e891a5d26221136d7334982fc2e99d3>>
+ * @generated SignedSource<<43b92dd984e985e09e3efad9c8fedf44>>
  */
 
 /**
@@ -159,6 +159,12 @@ class ReactNativeFeatureFlagsProviderHolder
     return method(javaProvider_);
   }
 
+  bool enablePreciseSchedulingForPremountItemsOnAndroid() override {
+    static const auto method =
+        getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("enablePreciseSchedulingForPremountItemsOnAndroid");
+    return method(javaProvider_);
+  }
+
   bool enablePropsUpdateReconciliationAndroid() override {
     static const auto method =
         getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("enablePropsUpdateReconciliationAndroid");
@@ -443,6 +449,11 @@ bool JReactNativeFeatureFlagsCxxInterop::enableMicrotasks(
   return ReactNativeFeatureFlags::enableMicrotasks();
 }
 
+bool JReactNativeFeatureFlagsCxxInterop::enablePreciseSchedulingForPremountItemsOnAndroid(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
+  return ReactNativeFeatureFlags::enablePreciseSchedulingForPremountItemsOnAndroid();
+}
+
 bool JReactNativeFeatureFlagsCxxInterop::enablePropsUpdateReconciliationAndroid(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
   return ReactNativeFeatureFlags::enablePropsUpdateReconciliationAndroid();
@@ -670,6 +681,9 @@ void JReactNativeFeatureFlagsCxxInterop::registerNatives() {
       makeNativeMethod(
         "enableMicrotasks",
         JReactNativeFeatureFlagsCxxInterop::enableMicrotasks),
+      makeNativeMethod(
+        "enablePreciseSchedulingForPremountItemsOnAndroid",
+        JReactNativeFeatureFlagsCxxInterop::enablePreciseSchedulingForPremountItemsOnAndroid),
       makeNativeMethod(
         "enablePropsUpdateReconciliationAndroid",
         JReactNativeFeatureFlagsCxxInterop::enablePropsUpdateReconciliationAndroid),

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<70edc4176da74aed5eaa1561a907a7ee>>
+ * @generated SignedSource<<54c94f9bfa07e41d978899dbce03469f>>
  */
 
 /**
@@ -90,6 +90,9 @@ class JReactNativeFeatureFlagsCxxInterop
   static bool enableMicrotasks(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 
+  static bool enablePreciseSchedulingForPremountItemsOnAndroid(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
+
   static bool enablePropsUpdateReconciliationAndroid(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlags.cpp

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<80b130f32b0bc59b9a9605777537feeb>>
+ * @generated SignedSource<<b04a641595d870bd9666281b3f0cfec5>>
  */
 
 /**
@@ -101,6 +101,10 @@ bool ReactNativeFeatureFlags::enableMicrotasks() {
   return getAccessor().enableMicrotasks();
 }
 
+bool ReactNativeFeatureFlags::enablePreciseSchedulingForPremountItemsOnAndroid() {
+  return getAccessor().enablePreciseSchedulingForPremountItemsOnAndroid();
+}
+
 bool ReactNativeFeatureFlags::enablePropsUpdateReconciliationAndroid() {
   return getAccessor().enablePropsUpdateReconciliationAndroid();
 }

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlags.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<3b5ff29faaf1575c051131bdf24a3237>>
+ * @generated SignedSource<<2cde82b474ab94cd05bdf5e04e700c13>>
  */
 
 /**
@@ -137,6 +137,11 @@ class ReactNativeFeatureFlags {
    */
   RN_EXPORT static bool enableMicrotasks();
 
+  /**
+   * Moves execution of pre-mount items to outside the choregrapher in the main thread, so we can estimate idle time more precisely (Android only).
+   */
+  RN_EXPORT static bool enablePreciseSchedulingForPremountItemsOnAndroid();
+
   /**
    * When enabled, Android will receive prop updates based on the differences between the last rendered shadow node and the last committed shadow node.
    */