Respect Fabric event coalescing keys on Android

Author: sorinc03

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

@@ -1108,8 +1108,6 @@ public void receiveEvent(
    * that C++ may coalesce the event optionally. Otherwise, coalescing can happen in Java before
    * emitting.
    *
-   * <p>{@code customCoalesceKey} is currently unused.
-   *
    * @param surfaceId
    * @param reactTag
    * @param eventName
@@ -1142,8 +1140,6 @@ public void receiveEvent(
    * that C++ may coalesce the event optionally. Otherwise, coalescing can happen in Java before
    * emitting.
    *
-   * <p>{@code customCoalesceKey} is currently unused.
-   *
    * @param surfaceId
    * @param reactTag
    * @param eventName
@@ -1179,8 +1175,6 @@ public void receiveEvent(
    * that C++ may coalesce the event optionally. Otherwise, coalescing can happen in Java before
    * emitting.
    *
-   * <p>{@code customCoalesceKey} is currently unused.
-   *
    * @param surfaceId
    * @param reactTag
    * @param eventName
@@ -1200,6 +1194,28 @@ public void receiveEvent(
       @EventCategoryDef int eventCategory,
       boolean experimentalIsSynchronous,
       long eventTimestamp) {
+    receiveEvent(
+        surfaceId,
+        reactTag,
+        eventName,
+        canCoalesceEvent,
+        params,
+        eventCategory,
+        experimentalIsSynchronous,
+        eventTimestamp,
+        0);
+  }
+
+  public void receiveEvent(
+      int surfaceId,
+      int reactTag,
+      String eventName,
+      boolean canCoalesceEvent,
+      @Nullable WritableMap params,
+      @EventCategoryDef int eventCategory,
+      boolean experimentalIsSynchronous,
+      long eventTimestamp,
+      int customCoalesceKey) {
 
     if (ReactBuildConfig.DEBUG && surfaceId == View.NO_ID) {
       FLog.d(TAG, "Emitted event without surfaceId: [%d] %s", reactTag, eventName);
@@ -1225,7 +1241,14 @@ public void receiveEvent(
     }
 
     mMountingManager.dispatchEvent(
-        surfaceId, reactTag, eventName, canCoalesceEvent, params, eventCategory, eventTimestamp);
+        surfaceId,
+        reactTag,
+        eventName,
+        canCoalesceEvent,
+        params,
+        eventCategory,
+        eventTimestamp,
+        customCoalesceKey);
   }
 
   @Override

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

@@ -40,6 +40,7 @@ internal class EventEmitterWrapper private constructor() : HybridClassBase() {
       eventName: String,
       params: NativeMap?,
       eventTimestamp: Long,
+      customCoalesceKey: Int,
   )
 
   /**
@@ -82,10 +83,29 @@ internal class EventEmitterWrapper private constructor() : HybridClassBase() {
    */
   @Synchronized
   fun dispatchUnique(eventName: String, params: WritableMap?, eventTimestamp: Long) {
+    dispatchUnique(eventName, params, eventTimestamp, 0)
+  }
+
+  /**
+   * Invokes the execution of the C++ EventEmitter. C++ will coalesce events sent to the same target
+   * with the same event name and coalescing key.
+   *
+   * @param eventName [String] name of the event to execute.
+   * @param params [WritableMap] payload of the event
+   * @param eventTimestamp timestamp when the event was triggered (in milliseconds since boot)
+   * @param customCoalesceKey key that determines which same-name events can coalesce together
+   */
+  @Synchronized
+  fun dispatchUnique(
+      eventName: String,
+      params: WritableMap?,
+      eventTimestamp: Long,
+      customCoalesceKey: Int,
+  ) {
     if (!isValid) {
       return
     }
-    dispatchUniqueEvent(eventName, params as NativeMap?, eventTimestamp)
+    dispatchUniqueEvent(eventName, params as NativeMap?, eventTimestamp, customCoalesceKey)
   }
 
   @Synchronized

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

@@ -58,6 +58,7 @@ internal class FabricEventEmitter(private val uiManager: FabricUIManager) : RCTM
           category,
           false,
           eventTimestamp,
+          customCoalesceKey,
       )
     } finally {
       Systrace.endSection(Systrace.TRACE_TAG_REACT)

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

@@ -335,6 +335,7 @@ internal class MountingManager(
       params: WritableMap?,
       @EventCategoryDef eventCategory: Int,
       eventTimestamp: Long,
+      customCoalesceKey: Int = 0,
   ) {
     val smm = getSurfaceMountingManager(surfaceId, reactTag)
     if (smm == null) {
@@ -347,7 +348,15 @@ internal class MountingManager(
       )
       return
     }
-    smm.dispatchEvent(reactTag, eventName, canCoalesceEvent, params, eventCategory, eventTimestamp)
+    smm.dispatchEvent(
+        reactTag,
+        eventName,
+        canCoalesceEvent,
+        params,
+        eventCategory,
+        eventTimestamp,
+        customCoalesceKey,
+    )
   }
 
   private fun getSurfaceMountingManager(surfaceId: Int, reactTag: Int): SurfaceMountingManager? =

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

@@ -1204,6 +1204,7 @@ internal constructor(
       params: WritableMap?,
       @EventCategoryDef eventCategory: Int,
       eventTimestamp: Long,
+      customCoalesceKey: Int = 0,
   ) {
     val viewState = registryGet(reactTag)
     if (viewState == null) {
@@ -1225,7 +1226,14 @@ internal constructor(
               viewState.pendingEventQueue
                   ?: LinkedList<PendingViewEvent>().also { viewState.pendingEventQueue = it }
           queue.add(
-              PendingViewEvent(eventName, params, eventCategory, canCoalesceEvent, eventTimestamp)
+              PendingViewEvent(
+                  eventName,
+                  params,
+                  eventCategory,
+                  canCoalesceEvent,
+                  eventTimestamp,
+                  customCoalesceKey,
+              )
           )
           return
         }
@@ -1241,7 +1249,7 @@ internal constructor(
 
     checkNotNull(emitter)
     if (canCoalesceEvent) {
-      emitter.dispatchUnique(eventName, params, eventTimestamp)
+      emitter.dispatchUnique(eventName, params, eventTimestamp, customCoalesceKey)
     } else {
       emitter.dispatch(eventName, params, eventCategory, eventTimestamp)
     }
@@ -1286,10 +1294,11 @@ internal constructor(
       @field:EventCategoryDef private val eventCategory: Int,
       private val canCoalesceEvent: Boolean,
       private val eventTimestamp: Long,
+      private val customCoalesceKey: Int,
   ) {
     fun dispatch(eventEmitter: EventEmitterWrapper) {
       if (canCoalesceEvent) {
-        eventEmitter.dispatchUnique(eventName, params, eventTimestamp)
+        eventEmitter.dispatchUnique(eventName, params, eventTimestamp, customCoalesceKey)
       } else {
         eventEmitter.dispatch(eventName, params, eventCategory, eventTimestamp)
       }

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/RCTModernEventEmitter.kt

@@ -30,7 +30,7 @@ public interface RCTModernEventEmitter : RCTEventEmitter {
 
   @Deprecated("Use the overload with eventTimestamp parameter instead.")
   public fun receiveEvent(surfaceId: Int, targetTag: Int, eventName: String, params: WritableMap?) {
-    // We assume this event can't be coalesced. `customCoalesceKey` has no meaning in Fabric.
+    // We assume this event can't be coalesced.
     receiveEvent(surfaceId, targetTag, eventName, false, 0, params, EventCategoryDef.UNSPECIFIED)
   }
 

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

@@ -66,15 +66,17 @@ void EventEmitterWrapper::dispatchEventSynchronously(
 void EventEmitterWrapper::dispatchUniqueEvent(
     std::string eventName,
     NativeMap* payload,
-    jlong eventTimestamp) {
+    jlong eventTimestamp,
+    int customCoalesceKey) {
   // 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->dispatchUniqueEvent(
         std::move(eventName),
         (payload != nullptr) ? payload->consume() : folly::dynamic::object(),
-        highResTimeStampFromMillis(eventTimestamp));
+        highResTimeStampFromMillis(eventTimestamp),
+        customCoalesceKey);
   }
 }
 

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

@@ -27,7 +27,11 @@ class EventEmitterWrapper : public jni::HybridClass<EventEmitterWrapper> {
 
   void dispatchEvent(std::string eventName, NativeMap *payload, int category, jlong eventTimestamp);
   void dispatchEventSynchronously(std::string eventName, NativeMap *params, jlong eventTimestamp);
-  void dispatchUniqueEvent(std::string eventName, NativeMap *payload, jlong eventTimestamp);
+  void dispatchUniqueEvent(
+      std::string eventName,
+      NativeMap *payload,
+      jlong eventTimestamp,
+      int customCoalesceKey);
 };
 
 } // namespace facebook::react

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/fabric/SurfaceMountingManagerEventOrderingTest.kt

@@ -167,7 +167,7 @@ class SurfaceMountingManagerEventOrderingTest {
     )
 
     verify(emitter, never()).dispatch(any(), any(), any(), any())
-    verify(emitter, never()).dispatchUnique(any(), any(), any())
+    verify(emitter, never()).dispatchUnique(any(), any(), any(), any())
     verifyNoMoreInteractions(emitter)
   }
 
@@ -179,10 +179,21 @@ class SurfaceMountingManagerEventOrderingTest {
 
     smm.dispatchEvent(reactTag, "topScroll", true, null, EventCategoryDef.UNSPECIFIED, 0L)
 
-    verify(emitter).dispatchUnique("topScroll", null, 0L)
+    verify(emitter).dispatchUnique("topScroll", null, 0L, 0)
     verify(emitter, never()).dispatch("topScroll", null, EventCategoryDef.UNSPECIFIED, 0L)
   }
 
+  @Test
+  fun dispatchEvent_forwardsCoalescingKey_forCoalesceableEvents() {
+    val smm = startSurfaceWithView()
+    val emitter: EventEmitterWrapper = mock()
+    smm.updateEventEmitter(reactTag, emitter)
+
+    smm.dispatchEvent(reactTag, "topScroll", true, null, EventCategoryDef.UNSPECIFIED, 0L, 7)
+
+    verify(emitter).dispatchUnique("topScroll", null, 0L, 7)
+  }
+
   @Test
   fun dispatchEvent_coalesceableEvents_drainedFromQueueUseDispatchUnique() {
     val smm = startSurfaceWithView()
@@ -192,7 +203,19 @@ class SurfaceMountingManagerEventOrderingTest {
     val emitter: EventEmitterWrapper = mock()
     smm.updateEventEmitter(reactTag, emitter)
 
-    verify(emitter).dispatchUnique("topScroll", null, 1L)
+    verify(emitter).dispatchUnique("topScroll", null, 1L, 0)
+  }
+
+  @Test
+  fun dispatchEvent_coalesceableEvents_drainedFromQueueForwardCoalescingKey() {
+    val smm = startSurfaceWithView()
+
+    smm.dispatchEvent(reactTag, "topScroll", true, null, EventCategoryDef.UNSPECIFIED, 1L, 9)
+
+    val emitter: EventEmitterWrapper = mock()
+    smm.updateEventEmitter(reactTag, emitter)
+
+    verify(emitter).dispatchUnique("topScroll", null, 1L, 9)
   }
 
   /** After a drain cycle, subsequent events should dispatch directly (fast path). */
@@ -308,7 +331,7 @@ class SurfaceMountingManagerEventOrderingTest {
 
     val ordered = inOrder(emitter)
     ordered.verify(emitter).dispatch("topChange", null, EventCategoryDef.UNSPECIFIED, 1L)
-    ordered.verify(emitter).dispatchUnique("topScroll", null, 2L)
+    ordered.verify(emitter).dispatchUnique("topScroll", null, 2L, 0)
     ordered.verify(emitter).dispatch("topFocus", null, EventCategoryDef.UNSPECIFIED, 3L)
   }