Add lock for surface presenter observers (#24052)

Summary:
Add lock for observers when do enumeration.
cc. shergin .

[iOS] [Fixed] - Add lock for surface presenter observers
Pull Request resolved: https://github.com/facebook/react-native/pull/24052

Differential Revision: D14619029

Pulled By: shergin

fbshipit-source-id: b843ac0e4b106a572de75663840f2e5e5f126f31

React/Fabric/RCTSurfacePresenter.mm

@@ -53,7 +53,7 @@ using namespace facebook::react;
   RCTBridge *_bridge; // Unsafe. We are moving away from Bridge.
   RCTBridge *_batchedBridge;
   std::shared_ptr<const ReactNativeConfig> _reactNativeConfig;
-  std::mutex _observerListMutex;
+  better::shared_mutex _observerListMutex;
   NSMutableArray<id<RCTSurfacePresenterObserver>> *_observers;
 }
 
@@ -319,13 +319,13 @@ using namespace facebook::react;
 
 - (void)addObserver:(id<RCTSurfacePresenterObserver>)observer
 {
-  std::lock_guard<std::mutex> lock(_observerListMutex);
+  std::unique_lock<better::shared_mutex> lock(_observerListMutex);
   [self->_observers addObject:observer];
 }
 
 - (void)removeObserver:(id<RCTSurfacePresenterObserver>)observer
 {
-  std::lock_guard<std::mutex> lock(_observerListMutex);
+  std::unique_lock<better::shared_mutex> lock(_observerListMutex);
   [self->_observers removeObject:observer];
 }
 
@@ -335,6 +335,7 @@ using namespace facebook::react;
 {
   RCTAssertMainQueue();
 
+  std::shared_lock<better::shared_mutex> lock(_observerListMutex);
   for (id<RCTSurfacePresenterObserver> observer in _observers) {
     if ([observer respondsToSelector:@selector(willMountComponentsWithRootTag:)]) {
       [observer willMountComponentsWithRootTag:rootTag];
@@ -355,6 +356,8 @@ using namespace facebook::react;
       surface.view.rootView = (RCTSurfaceRootView *)rootComponentView;
     }
   }
+
+  std::shared_lock<better::shared_mutex> lock(_observerListMutex);
   for (id<RCTSurfacePresenterObserver> observer in _observers) {
     if ([observer respondsToSelector:@selector(didMountComponentsWithRootTag:)]) {
       [observer didMountComponentsWithRootTag:rootTag];