Implement potential fix for mounting errors during synchronous state …

…updates (v2) (facebook#44492)

Summary:

Changelog: [internal]

This is a new attempt at fixing mounting errors during synchronous state updates after what we tried in facebook#44015.

That fix didn't work because `dispatchMountItems` actually makes a copy of the mount items that it's going to process, so when we added the mount items to the list they were actually not being picked up by the current processing.

This changes the fix to expose a new list of mount items being processed, and if that's defined then we add it to the list. Otherwise we process as usual.

Reviewed By: sammy-SC

Differential Revision: D57107212

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

@@ -208,10 +208,7 @@ public void executeItems(Queue<MountItem> items) {
           // This executor can be technically accessed before the dispatcher is created,
           // but if that happens, something is terribly wrong
           if (ReactNativeFeatureFlags.forceBatchingMountItemsOnAndroid()) {
-            for (MountItem mountItem : items) {
-              mMountItemDispatcher.addMountItem(mountItem);
-            }
-            mMountItemDispatcher.tryDispatchMountItems();
+            mMountItemDispatcher.batchMountItemsIfNecessary(items);
           } else {
             mMountItemDispatcher.dispatchMountItems(items);
           }

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

@@ -48,6 +48,8 @@ public class MountItemDispatcher {
   @NonNull
   private final ConcurrentLinkedQueue<MountItem> mMountItems = new ConcurrentLinkedQueue<>();
 
+  @Nullable private List<MountItem> mCurrentMountItemsBatch;
+
   @NonNull
   private final ConcurrentLinkedQueue<MountItem> mPreMountItems = new ConcurrentLinkedQueue<>();
 
@@ -69,6 +71,16 @@ public void addMountItem(MountItem mountItem) {
     mMountItems.add(mountItem);
   }
 
+  @UiThread
+  @ThreadConfined(UI)
+  public void batchMountItemsIfNecessary(Queue<MountItem> items) {
+    if (mCurrentMountItemsBatch != null) {
+      mCurrentMountItemsBatch.addAll(items);
+    } else {
+      dispatchMountItems(items);
+    }
+  }
+
   public void addPreAllocateMountItem(MountItem mountItem) {
     // We do this check only for PreAllocateViewMountItem - and not DispatchMountItem or regular
     // MountItem - because PreAllocateViewMountItems are not batched, and is relatively more
@@ -103,10 +115,6 @@ public void tryDispatchMountItems() {
       return;
     }
 
-    if (ReactNativeFeatureFlags.forceBatchingMountItemsOnAndroid()) {
-      mInDispatch = true;
-    }
-
     final boolean didDispatchItems;
     try {
       didDispatchItems = dispatchMountItems();
@@ -189,6 +197,10 @@ private boolean dispatchMountItems() {
         getAndResetViewCommandMountItems();
     List<MountItem> mountItemsToDispatch = getAndResetMountItems();
 
+    if (ReactNativeFeatureFlags.forceBatchingMountItemsOnAndroid()) {
+      mCurrentMountItemsBatch = mountItemsToDispatch;
+    }
+
     if (mountItemsToDispatch == null && viewCommandMountItemsToDispatch == null) {
       return false;
     }
@@ -305,6 +317,8 @@ private boolean dispatchMountItems() {
 
     mItemDispatchListener.didMountItems(mountItemsToDispatch);
 
+    mCurrentMountItemsBatch = null;
+
     Systrace.endSection(Systrace.TRACE_TAG_REACT_JAVA_BRIDGE);
 
     return true;