Fabric: Simplified relationship between RawEvent and EventEmitter

Summary: Instead of relying on explicit `RawEventDispatchable` function, we simply check the existence of the `weak_ptr` to `EventTarget`. This is efficient and sufficient because only an EventEmitter retains an associated EventTarget.

Reviewed By: mdvacca

Differential Revision: D9764858

fbshipit-source-id: 4ac25d925f189d0f8b9002e52388fd51629934a8

ReactCommon/fabric/events/EventEmitter.cpp

@@ -45,7 +45,7 @@ void EventEmitter::dispatchEvent(
   const folly::dynamic &payload,
   const EventPriority &priority
 ) const {
-  const auto &eventDispatcher = eventDispatcher_.lock();
+  auto eventDispatcher = eventDispatcher_.lock();
   if (!eventDispatcher) {
     return;
   }
@@ -55,21 +55,11 @@ void EventEmitter::dispatchEvent(
   folly::dynamic extendedPayload = folly::dynamic::object("target", tag_);
   extendedPayload.merge_patch(payload);
 
-  auto weakEventEmitter = std::weak_ptr<const EventEmitter> {shared_from_this()};
-
   eventDispatcher->dispatchEvent(
     RawEvent(
       normalizeEventType(type),
       extendedPayload,
-      eventTarget_,
-      [weakEventEmitter]() {
-        auto eventEmitter = weakEventEmitter.lock();
-        if (!eventEmitter) {
-          return false;
-        }
-
-        return eventEmitter->getEnabled();
-      }
+      eventTarget_
     ),
     priority
   );

ReactCommon/fabric/events/EventEmitter.h

@@ -33,8 +33,7 @@ using SharedEventEmitter = std::shared_ptr<const EventEmitter>;
  * JSI maintains `WeakObject` object as long as we retain the `EventTarget`.
  * All `EventTarget` instances must be deallocated before stopping JavaScript machine.
  */
-class EventEmitter:
-  public std::enable_shared_from_this<EventEmitter> {
+class EventEmitter {
 
   /*
    * We have to repeat `Tag` type definition here because `events` module does

ReactCommon/fabric/events/EventQueue.cpp

@@ -39,10 +39,10 @@ void EventQueue::onBeat() const {
 
   {
     std::lock_guard<std::recursive_mutex> lock(EventEmitter::DispatchMutex());
+
     for (const auto &event : queue) {
-      auto eventTarget = event.eventTarget.lock();
       eventPipe_(
-        eventTarget && event.isDispatchable() ? eventTarget.get() : nullptr,
+        event.eventTarget.lock().get(),
         event.type,
         event.payload
       );

ReactCommon/fabric/events/RawEvent.cpp

@@ -13,17 +13,11 @@ namespace react {
 RawEvent::RawEvent(
   std::string type,
   folly::dynamic payload,
-  WeakEventTarget eventTarget,
-  RawEventDispatchable isDispatchable
+  WeakEventTarget eventTarget
 ):
   type(std::move(type)),
   payload(std::move(payload)),
-  eventTarget(std::move(eventTarget)),
-  isDispatchable_(std::move(isDispatchable)) {}
-
-bool RawEvent::isDispatchable() const {
-  return isDispatchable_();
-}
+  eventTarget(std::move(eventTarget)) {}
 
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/events/RawEvent.h

@@ -15,33 +15,20 @@ namespace facebook {
 namespace react {
 
 /*
- * Represents ready-to-dispatch event data.
+ * Represents ready-to-dispatch event object.
  */
 class RawEvent {
 
 public:
-  using RawEventDispatchable = std::function<bool()>;
-
   RawEvent(
     std::string type,
     folly::dynamic payload,
-    WeakEventTarget eventTarget,
-    RawEventDispatchable isDispatchable
+    WeakEventTarget eventTarget
   );
 
   const std::string type;
   const folly::dynamic payload;
   const WeakEventTarget eventTarget;
-
-  /*
-   * Returns `true` if event can be dispatched to `eventTarget`.
-   * Events that associated with unmounted or deallocated `ShadowNode`s
-   * must not be dispatched.
-   */
-  bool isDispatchable() const;
-
-private:
-  const RawEventDispatchable isDispatchable_;
 };
 
 } // namespace react