From 17f4c45eed420f2a0f8fc17a4e145991dcc279ba Mon Sep 17 00:00:00 2001
From: Pieter De Baets <pieterdb@meta.com>
Date: Wed, 2 Oct 2024 05:10:49 -0700
Subject: [PATCH] Add missing lock in ReactInstanceManager#attachRootView
 (#46776)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/46776

All other paths that touch `mAttachedReactRoots` uses this lock. We expect this to address a crash we're seeing in production where `startSurface` is invoked multiple times.

Changelog: [Internal]

Reviewed By: fabriziocucci

Differential Revision: D63752083

fbshipit-source-id: f06d07aa70719945f6956fbf6e0cde3e9c8e8ed0
---
 .../facebook/react/ReactInstanceManager.java  | 31 ++++++++++---------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java
index 31cf7f73823..4730646870c 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java
@@ -942,22 +942,23 @@ public class ReactInstanceManager {
   @ThreadConfined(UI)
   public void attachRootView(ReactRoot reactRoot) {
     UiThreadUtil.assertOnUiThread();
+    synchronized (mAttachedReactRoots) {
+      // Calling clearReactRoot is necessary to initialize the Id on reactRoot
+      // This is necessary independently if the RN Bridge has been initialized or not.
+      // Ideally reactRoot should be initialized with id == NO_ID
+      if (mAttachedReactRoots.add(reactRoot)) {
+        clearReactRoot(reactRoot);
+      } else {
+        FLog.e(ReactConstants.TAG, "ReactRoot was attached multiple times");
+      }
 
-    // Calling clearReactRoot is necessary to initialize the Id on reactRoot
-    // This is necessary independently if the RN Bridge has been initialized or not.
-    // Ideally reactRoot should be initialized with id == NO_ID
-    if (mAttachedReactRoots.add(reactRoot)) {
-      clearReactRoot(reactRoot);
-    } else {
-      FLog.e(ReactConstants.TAG, "ReactRoot was attached multiple times");
-    }
-
-    // If react context is being created in the background, JS application will be started
-    // automatically when creation completes, as reactRoot is part of the attached
-    // reactRoot list.
-    ReactContext currentContext = getCurrentReactContext();
-    if (mCreateReactContextThread == null && currentContext != null) {
-      attachRootViewToInstance(reactRoot);
+      // If react context is being created in the background, JS application will be started
+      // automatically when creation completes, as reactRoot is part of the attached
+      // reactRoot list.
+      ReactContext currentContext = getCurrentReactContext();
+      if (mCreateReactContextThread == null && currentContext != null) {
+        attachRootViewToInstance(reactRoot);
+      }
     }
   }