Schedule JS revision merge on the main thread

packages/react-native/React/Fabric/RCTScheduler.h

@@ -31,6 +31,8 @@ NS_ASSUME_NONNULL_BEGIN
 - (void)schedulerShouldRenderTransactions:
     (std::shared_ptr<const facebook::react::MountingCoordinator>)mountingCoordinator;
 
+- (void)schedulerShouldMergeReactRevision:(facebook::react::SurfaceId)surfaceId;
+
 - (void)schedulerDidDispatchCommand:(const facebook::react::ShadowView &)shadowView
                         commandName:(const std::string &)commandName
                                args:(const folly::dynamic &)args;

packages/react-native/React/Fabric/RCTScheduler.mm

@@ -36,6 +36,12 @@ void schedulerShouldRenderTransactions(const std::shared_ptr<const MountingCoord
     [scheduler.delegate schedulerShouldRenderTransactions:mountingCoordinator];
   }
 
+  void schedulerShouldMergeReactRevision(SurfaceId surfaceId) override
+  {
+    RCTScheduler *scheduler = (__bridge RCTScheduler *)scheduler_;
+    [scheduler.delegate schedulerShouldMergeReactRevision:surfaceId];
+  }
+
   void schedulerDidRequestPreliminaryViewAllocation(const ShadowNode &shadowNode) override
   {
     // Does nothing.

packages/react-native/React/Fabric/RCTSurfacePresenter.mm

@@ -307,6 +307,16 @@ - (void)schedulerShouldRenderTransactions:(std::shared_ptr<const MountingCoordin
   [_mountingManager scheduleTransaction:mountingCoordinator];
 }
 
+- (void)schedulerShouldMergeReactRevision:(SurfaceId)surfaceId
+{
+  auto scheduler = [self scheduler];
+  RCTExecuteOnMainQueue(^{
+    RCTAssertMainQueue();
+    scheduler.uiManager->getShadowTreeRegistry().visit(
+        surfaceId, [](const ShadowTree &shadowTree) { shadowTree.mergeReactRevision(); });
+  });
+}
+
 - (void)schedulerDidDispatchCommand:(const ShadowView &)shadowView
                         commandName:(const std::string &)commandName
                                args:(const folly::dynamic &)args

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

@@ -959,6 +959,19 @@ public void runGuarded() {
     }
   }
 
+  @SuppressWarnings("unused")
+  @AnyThread
+  @ThreadConfined(ANY)
+  private void scheduleReactRevisionMerge(int surfaceId) {
+    UiThreadUtil.runOnUiThread(
+        () -> {
+          FabricUIManagerBinding binding = mBinding;
+          if (binding != null) {
+            binding.mergeReactRevision(surfaceId);
+          }
+        });
+  }
+
   /**
    * This method initiates preloading of an image specified by ImageSource. It can later be consumed
    * by an ImageView.

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManagerBinding.kt

@@ -83,6 +83,8 @@ internal class FabricUIManagerBinding : HybridClassBase() {
 
   external fun reportMount(surfaceId: Int)
 
+  external fun mergeReactRevision(surfaceId: Int)
+
   fun register(
       runtimeExecutor: RuntimeExecutor,
       runtimeScheduler: RuntimeScheduler,

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<<adc6b24ae04487d2b82a2bac35f027a7>>
+ * @generated SignedSource<<41608741730ad508aab1b24e0183ef85>>
  */
 
 /**
@@ -168,6 +168,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun enableExclusivePropsUpdateAndroid(): Boolean = accessor.enableExclusivePropsUpdateAndroid()
 
+  /**
+   * Enables Fabric commit branching to fix starvation problems and atomic JS updates.
+   */
+  @JvmStatic
+  public fun enableFabricCommitBranching(): Boolean = accessor.enableFabricCommitBranching()
+
   /**
    * This feature flag enables logs for Fabric.
    */

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<<3ebb3c265193b4f61e5bf43082c5be54>>
+ * @generated SignedSource<<afe25c0d026ce69bb3d08e3631cee312>>
  */
 
 /**
@@ -43,6 +43,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var enableEagerMainQueueModulesOnIOSCache: Boolean? = null
   private var enableEagerRootViewAttachmentCache: Boolean? = null
   private var enableExclusivePropsUpdateAndroidCache: Boolean? = null
+  private var enableFabricCommitBranchingCache: Boolean? = null
   private var enableFabricLogsCache: Boolean? = null
   private var enableFabricRendererCache: Boolean? = null
   private var enableFontScaleChangesUpdatingLayoutCache: Boolean? = null
@@ -318,6 +319,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun enableFabricCommitBranching(): Boolean {
+    var cached = enableFabricCommitBranchingCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.enableFabricCommitBranching()
+      enableFabricCommitBranchingCache = cached
+    }
+    return cached
+  }
+
   override fun enableFabricLogs(): Boolean {
     var cached = enableFabricLogsCache
     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<<eb11cf643c4e94eddc5d7985a8a7a03a>>
+ * @generated SignedSource<<1547e15c25a3a1fe1a6223c77e60d874>>
  */
 
 /**
@@ -74,6 +74,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun enableExclusivePropsUpdateAndroid(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun enableFabricCommitBranching(): Boolean
+
   @DoNotStrip @JvmStatic public external fun enableFabricLogs(): Boolean
 
   @DoNotStrip @JvmStatic public external fun enableFabricRenderer(): 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<<bb85527f5c9affa81a1ea33f2873a957>>
+ * @generated SignedSource<<9bc1dd6111373452e7246ee3682f7e7c>>
  */
 
 /**
@@ -69,6 +69,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun enableExclusivePropsUpdateAndroid(): Boolean = false
 
+  override fun enableFabricCommitBranching(): Boolean = false
+
   override fun enableFabricLogs(): Boolean = false
 
   override fun enableFabricRenderer(): 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<<f9ee0d1f23024b026d065ffc3d48cfcf>>
+ * @generated SignedSource<<48bf1cbc2c442a6faa0bf64dea60b046>>
  */
 
 /**
@@ -47,6 +47,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var enableEagerMainQueueModulesOnIOSCache: Boolean? = null
   private var enableEagerRootViewAttachmentCache: Boolean? = null
   private var enableExclusivePropsUpdateAndroidCache: Boolean? = null
+  private var enableFabricCommitBranchingCache: Boolean? = null
   private var enableFabricLogsCache: Boolean? = null
   private var enableFabricRendererCache: Boolean? = null
   private var enableFontScaleChangesUpdatingLayoutCache: Boolean? = null
@@ -345,6 +346,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun enableFabricCommitBranching(): Boolean {
+    var cached = enableFabricCommitBranchingCache
+    if (cached == null) {
+      cached = currentProvider.enableFabricCommitBranching()
+      accessedFeatureFlags.add("enableFabricCommitBranching")
+      enableFabricCommitBranchingCache = cached
+    }
+    return cached
+  }
+
   override fun enableFabricLogs(): Boolean {
     var cached = enableFabricLogsCache
     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<<09cef8cedd515f477a32c2ed77d86fc4>>
+ * @generated SignedSource<<b2358b8652510cd6aa9381a45049ee30>>
  */
 
 /**
@@ -69,6 +69,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun enableExclusivePropsUpdateAndroid(): Boolean
 
+  @DoNotStrip public fun enableFabricCommitBranching(): Boolean
+
   @DoNotStrip public fun enableFabricLogs(): Boolean
 
   @DoNotStrip public fun enableFabricRenderer(): Boolean

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricMountingManager.cpp

@@ -1206,4 +1206,11 @@ void FabricMountingManager::synchronouslyUpdateViewOnUIThread(
   synchronouslyUpdateViewOnUIThreadJNI(javaUIManager_, viewTag, propsMap);
 }
 
+void FabricMountingManager::scheduleReactRevisionMerge(SurfaceId surfaceId) {
+  static const auto scheduleReactRevisionMerge =
+      JFabricUIManager::javaClassStatic()->getMethod<void(int32_t)>(
+          "scheduleReactRevisionMerge");
+  scheduleReactRevisionMerge(javaUIManager_, surfaceId);
+}
+
 } // namespace facebook::react

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricMountingManager.h

@@ -54,6 +54,8 @@ class FabricMountingManager final {
 
   void synchronouslyUpdateViewOnUIThread(Tag viewTag, const folly::dynamic &props);
 
+  void scheduleReactRevisionMerge(SurfaceId surfaceId);
+
  private:
   bool isOnMainThread();
 

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricUIManagerBinding.cpp

@@ -685,6 +685,23 @@ void FabricUIManagerBinding::schedulerShouldRenderTransactions(
   }
 }
 
+void FabricUIManagerBinding::schedulerShouldMergeReactRevision(
+    SurfaceId surfaceId) {
+  std::shared_lock lock(installMutex_);
+  auto mountingManager =
+      getMountingManager("schedulerShouldMergeReactRevision");
+  if (mountingManager) {
+    mountingManager->scheduleReactRevisionMerge(surfaceId);
+  }
+}
+
+void FabricUIManagerBinding::mergeReactRevision(SurfaceId surfaceId) {
+  std::shared_lock lock(installMutex_);
+  scheduler_->getUIManager()->getShadowTreeRegistry().visit(
+      surfaceId,
+      [](const ShadowTree& shadowTree) { shadowTree.mergeReactRevision(); });
+}
+
 void FabricUIManagerBinding::schedulerDidRequestPreliminaryViewAllocation(
     const ShadowNode& shadowNode) {
   using namespace std::literals::string_view_literals;
@@ -816,6 +833,8 @@ void FabricUIManagerBinding::registerNatives() {
       makeNativeMethod(
           "getRelativeAncestorList",
           FabricUIManagerBinding::getRelativeAncestorList),
+      makeNativeMethod(
+          "mergeReactRevision", FabricUIManagerBinding::mergeReactRevision),
   });
 }
 

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricUIManagerBinding.h

@@ -96,6 +96,10 @@ class FabricUIManagerBinding : public jni::HybridClass<FabricUIManagerBinding>,
   void schedulerShouldRenderTransactions(
       const std::shared_ptr<const MountingCoordinator> &mountingCoordinator) override;
 
+  void schedulerShouldMergeReactRevision(SurfaceId surfaceId) override;
+
+  void mergeReactRevision(SurfaceId surfaceId);
+
   void schedulerDidRequestPreliminaryViewAllocation(const ShadowNode &shadowNode) override;
 
   void schedulerDidDispatchCommand(

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<<b9af351de972ddff807bd25f98f3ff42>>
+ * @generated SignedSource<<74926c76bdfbb63f36baca7804123cfb>>
  */
 
 /**
@@ -177,6 +177,12 @@ class ReactNativeFeatureFlagsJavaProvider
     return method(javaProvider_);
   }
 
+  bool enableFabricCommitBranching() override {
+    static const auto method =
+        getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("enableFabricCommitBranching");
+    return method(javaProvider_);
+  }
+
   bool enableFabricLogs() override {
     static const auto method =
         getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("enableFabricLogs");
@@ -698,6 +704,11 @@ bool JReactNativeFeatureFlagsCxxInterop::enableExclusivePropsUpdateAndroid(
   return ReactNativeFeatureFlags::enableExclusivePropsUpdateAndroid();
 }
 
+bool JReactNativeFeatureFlagsCxxInterop::enableFabricCommitBranching(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
+  return ReactNativeFeatureFlags::enableFabricCommitBranching();
+}
+
 bool JReactNativeFeatureFlagsCxxInterop::enableFabricLogs(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
   return ReactNativeFeatureFlags::enableFabricLogs();
@@ -1133,6 +1144,9 @@ void JReactNativeFeatureFlagsCxxInterop::registerNatives() {
       makeNativeMethod(
         "enableExclusivePropsUpdateAndroid",
         JReactNativeFeatureFlagsCxxInterop::enableExclusivePropsUpdateAndroid),
+      makeNativeMethod(
+        "enableFabricCommitBranching",
+        JReactNativeFeatureFlagsCxxInterop::enableFabricCommitBranching),
       makeNativeMethod(
         "enableFabricLogs",
         JReactNativeFeatureFlagsCxxInterop::enableFabricLogs),

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<<c89b15dbb7d1cec571eed1551e1b7162>>
+ * @generated SignedSource<<d2e7a278fd4b8f8308d1a7c402c4f227>>
  */
 
 /**
@@ -99,6 +99,9 @@ class JReactNativeFeatureFlagsCxxInterop
   static bool enableExclusivePropsUpdateAndroid(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 
+  static bool enableFabricCommitBranching(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
+
   static bool enableFabricLogs(
     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<<08d50062a88a227aa8800e549b6dfe57>>
+ * @generated SignedSource<<a1fd11b8f74ba91dfc9ed24c61fb36e9>>
  */
 
 /**
@@ -118,6 +118,10 @@ bool ReactNativeFeatureFlags::enableExclusivePropsUpdateAndroid() {
   return getAccessor().enableExclusivePropsUpdateAndroid();
 }
 
+bool ReactNativeFeatureFlags::enableFabricCommitBranching() {
+  return getAccessor().enableFabricCommitBranching();
+}
+
 bool ReactNativeFeatureFlags::enableFabricLogs() {
   return getAccessor().enableFabricLogs();
 }

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<<4f6913d92515fd817a167ef2a505c777>>
+ * @generated SignedSource<<5ae45db772734aa6c657de764f5ebcf8>>
  */
 
 /**
@@ -154,6 +154,11 @@ class ReactNativeFeatureFlags {
    */
   RN_EXPORT static bool enableExclusivePropsUpdateAndroid();
 
+  /**
+   * Enables Fabric commit branching to fix starvation problems and atomic JS updates.
+   */
+  RN_EXPORT static bool enableFabricCommitBranching();
+
   /**
    * This feature flag enables logs for Fabric.
    */