Add native synchronous event support (facebook#44451)

Summary:

Changelog: [internal]

Exposing the experimental API EventEmitter::experimental_flushSync to trigger synchronous events from Android. The API will be changed in the future, this is exposed only for experimentation.

Reviewed By: NickGerleman

Differential Revision: D56886402

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

@@ -40,6 +40,8 @@ private EventEmitterWrapper(HybridData hybridData) {
   private native void dispatchEvent(
       String eventName, @Nullable NativeMap params, @EventCategoryDef int category);
 
+  private native void dispatchEventSynchronously(String eventName, @Nullable NativeMap params);
+
   private native void dispatchUniqueEvent(String eventName, @Nullable NativeMap params);
 
   /**

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

@@ -27,6 +27,22 @@ void EventEmitterWrapper::dispatchEvent(
   }
 }
 
+void EventEmitterWrapper::dispatchEventSynchronously(
+    std::string eventName,
+    NativeMap* params) {
+  // It is marginal, but possible for this to be constructed without a valid
+  // EventEmitter. In those cases, make sure we noop/blackhole events instead of
+  // crashing.
+  if (eventEmitter != nullptr) {
+    eventEmitter->experimental_flushSync([&]() {
+      eventEmitter->dispatchEvent(
+          std::move(eventName),
+          (params != nullptr) ? params->consume() : folly::dynamic::object(),
+          RawEvent::Category::Discrete);
+    });
+  }
+}
+
 void EventEmitterWrapper::dispatchUniqueEvent(
     std::string eventName,
     NativeMap* payload) {
@@ -44,6 +60,9 @@ void EventEmitterWrapper::registerNatives() {
       makeNativeMethod("dispatchEvent", EventEmitterWrapper::dispatchEvent),
       makeNativeMethod(
           "dispatchUniqueEvent", EventEmitterWrapper::dispatchUniqueEvent),
+      makeNativeMethod(
+          "dispatchEventSynchronously",
+          EventEmitterWrapper::dispatchEventSynchronously),
   });
 }
 

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

@@ -28,6 +28,7 @@ class EventEmitterWrapper : public jni::HybridClass<EventEmitterWrapper> {
   SharedEventEmitter eventEmitter;
 
   void dispatchEvent(std::string eventName, NativeMap* params, int category);
+  void dispatchEventSynchronously(std::string eventName, NativeMap* params);
   void dispatchUniqueEvent(std::string eventName, NativeMap* params);
 };