Fabric: Exposing EventEmitter's ownership model as a shared_ptr

Summary:
As we did in the previous diff, here we implemented `EventEmitter`'s ownership model as a `shared_ptr`. This change fixes problem with leaking `WeakObject`s which happens on hot-reload.

So, in short:
 * `EventTargetWrapper` object owns `jsi::WeakObject` that can be converted to actual `jsi::Object` that represent event target in JavaScript realm;
 * `EventTargetWrapper` and `jsi::WeakObject` objects must be deallocated as soon as native part does not need them anymore;
 * `EventEmitter` objects retain `EventTarget` objects;
 * `EventEmitter` can loose event target object in case if assosiated `ShadowNode` got unmounted (not deallocated); in this case `EventEmitter` is loosing possibility to dispatch event even if some mounting-layer code is still retaining it.

Reviewed By: mdvacca

Differential Revision: D9762755

fbshipit-source-id: 96e989767a32914db9f4627fce51b044c71f257a

ReactCommon/fabric/core/componentdescriptor/ComponentDescriptor.h

@@ -80,7 +80,7 @@ public:
    * shadow nodes.
    */
   virtual SharedEventEmitter createEventEmitter(
-    const EventTarget &eventTarget,
+    SharedEventTarget eventTarget,
     const Tag &tag
   ) const = 0;
 };

ReactCommon/fabric/core/componentdescriptor/ConcreteComponentDescriptor.h

@@ -92,10 +92,10 @@ public:
   };
 
   virtual SharedEventEmitter createEventEmitter(
-    const EventTarget &eventTarget,
+    SharedEventTarget eventTarget,
     const Tag &tag
   ) const override {
-    return std::make_shared<ConcreteEventEmitter>(eventTarget, tag, eventDispatcher_);
+    return std::make_shared<ConcreteEventEmitter>(std::move(eventTarget), tag, eventDispatcher_);
   }
 
 protected:

ReactCommon/fabric/events/EventDispatcher.h

@@ -18,6 +18,7 @@ namespace react {
 
 class EventDispatcher;
 using SharedEventDispatcher = std::shared_ptr<const EventDispatcher>;
+using WeakEventDispatcher = std::weak_ptr<const EventDispatcher>;
 
 /*
  * Represents event-delivery infrastructure.

ReactCommon/fabric/events/EventEmitter.cpp

@@ -31,10 +31,14 @@ std::recursive_mutex &EventEmitter::DispatchMutex() {
   return mutex;
 }
 
-EventEmitter::EventEmitter(const EventTarget &eventTarget, const Tag &tag, const std::shared_ptr<const EventDispatcher> &eventDispatcher):
-  eventTarget_(eventTarget),
+EventEmitter::EventEmitter(
+  SharedEventTarget eventTarget,
+  Tag tag,
+  WeakEventDispatcher eventDispatcher
+):
+  eventTarget_(std::move(eventTarget)),
   tag_(tag),
-  eventDispatcher_(eventDispatcher) {}
+  eventDispatcher_(std::move(eventDispatcher)) {}
 
 void EventEmitter::dispatchEvent(
   const std::string &type,
@@ -73,6 +77,9 @@ void EventEmitter::dispatchEvent(
 
 void EventEmitter::setEnabled(bool enabled) const {
   enabled_ = enabled;
+  if (!enabled) {
+    eventTarget_ = nullptr;
+  }
 }
 
 bool EventEmitter::getEnabled() const {

ReactCommon/fabric/events/EventEmitter.h

@@ -22,8 +22,16 @@ using SharedEventEmitter = std::shared_ptr<const EventEmitter>;
 
 /*
  * Base class for all particular typed event handlers.
- * Stores `InstanceHandle` identifying a particular component and the pointer
- * to `EventDispatcher` which is responsible for delivering the event.
+ * Stores a pointer to `EventTarget` identifying a particular component and
+ * a weak pointer to `EventDispatcher` which is responsible for delivering the event.
+ *
+ * Note: Retaining an `EventTarget` does *not* guarantee that actual event target
+ * exists and/or valid in JavaScript realm. The `EventTarget` retains an `EventTargetWrapper`
+ * which wraps JavaScript object in `unsafe-unretained` manner. Retaining
+ * the `EventTarget` *does* indicate that we can use that to get an actual
+ * JavaScript object from that in the future *ensuring safety beforehand somehow*;
+ * 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> {
@@ -37,7 +45,12 @@ class EventEmitter:
 public:
   static std::recursive_mutex &DispatchMutex();
 
-  EventEmitter(const EventTarget &eventTarget, const Tag &tag, const std::shared_ptr<const EventDispatcher> &eventDispatcher);
+  EventEmitter(
+    SharedEventTarget eventTarget,
+    Tag tag,
+    WeakEventDispatcher eventDispatcher
+  );
+
   virtual ~EventEmitter() = default;
 
   /*
@@ -59,9 +72,9 @@ protected:
   ) const;
 
 private:
-  EventTarget eventTarget_;
+  mutable SharedEventTarget eventTarget_;
   Tag tag_;
-  std::weak_ptr<const EventDispatcher> eventDispatcher_;
+  WeakEventDispatcher eventDispatcher_;
   mutable bool enabled_; // Protected by `DispatchMutex`.
 };
 

ReactCommon/fabric/events/EventQueue.cpp

@@ -12,8 +12,8 @@
 namespace facebook {
 namespace react {
 
-EventQueue::EventQueue(const EventPipe &eventPipe, std::unique_ptr<EventBeat> eventBeat):
-  eventPipe_(eventPipe),
+EventQueue::EventQueue(EventPipe eventPipe, std::unique_ptr<EventBeat> eventBeat):
+  eventPipe_(std::move(eventPipe)),
   eventBeat_(std::move(eventBeat)) {
     eventBeat_->setBeatCallback(std::bind(&EventQueue::onBeat, this));
   }
@@ -40,8 +40,9 @@ void EventQueue::onBeat() const {
   {
     std::lock_guard<std::recursive_mutex> lock(EventEmitter::DispatchMutex());
     for (const auto &event : queue) {
+      auto eventTarget = event.eventTarget.lock();
       eventPipe_(
-        event.isDispachable() ? event.eventTarget : EmptyEventTarget,
+        eventTarget && event.isDispatchable() ? eventTarget.get() : nullptr,
         event.type,
         event.payload
       );

ReactCommon/fabric/events/EventQueue.h

@@ -25,7 +25,7 @@ namespace react {
 class EventQueue {
 
 public:
-  EventQueue(const EventPipe &eventPipe, std::unique_ptr<EventBeat> eventBeat);
+  EventQueue(EventPipe eventPipe, std::unique_ptr<EventBeat> eventBeat);
   virtual ~EventQueue() = default;
 
   /*

ReactCommon/fabric/events/RawEvent.cpp

@@ -11,18 +11,18 @@ namespace facebook {
 namespace react {
 
 RawEvent::RawEvent(
-  const std::string &type,
-  const folly::dynamic &payload,
-  const EventTarget &eventTarget,
-  const std::function<bool()> &isDispatchable
+  std::string type,
+  folly::dynamic payload,
+  WeakEventTarget eventTarget,
+  RawEventDispatchable isDispatchable
 ):
-  type(type),
-  payload(payload),
-  eventTarget(eventTarget),
-  isDispachable_(isDispatchable) {}
+  type(std::move(type)),
+  payload(std::move(payload)),
+  eventTarget(std::move(eventTarget)),
+  isDispatchable_(std::move(isDispatchable)) {}
 
-bool RawEvent::isDispachable() const {
-  return isDispachable_();
+bool RawEvent::isDispatchable() const {
+  return isDispatchable_();
 }
 
 } // namespace react

ReactCommon/fabric/events/RawEvent.h

@@ -23,25 +23,25 @@ public:
   using RawEventDispatchable = std::function<bool()>;
 
   RawEvent(
-    const std::string &type,
-    const folly::dynamic &payload,
-    const EventTarget &eventTarget,
-    const RawEventDispatchable &isDispachable
+    std::string type,
+    folly::dynamic payload,
+    WeakEventTarget eventTarget,
+    RawEventDispatchable isDispatchable
   );
 
   const std::string type;
   const folly::dynamic payload;
-  const EventTarget eventTarget;
+  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 isDispachable() const;
+  bool isDispatchable() const;
 
 private:
-  const RawEventDispatchable isDispachable_;
+  const RawEventDispatchable isDispatchable_;
 };
 
 } // namespace react

ReactCommon/fabric/events/primitives.h

@@ -24,28 +24,17 @@ enum class EventPriority: int {
   Deferred = AsynchronousBatched
 };
 
-/* `InstanceHandler`, `EventTarget`, and `EventHandler` are all opaque
- * raw pointers. We use `struct {} *` trick to differentiate them in compiler's
- * eyes to ensure type safety.
- * These structs must have names (and the names must be exported)
- * to allow consistent template (e.g. `std::function`) instantiating
- * across different modules.
- */
-using EventTarget = struct EventTargetDummyStruct {} *;
-
 /*
  * We need this types only to ensure type-safety when we deal with them. Conceptually,
  * they are opaque pointers to some types that derived from those classes.
  */
 class EventHandler {};
+class EventTarget {};
+using SharedEventHandler = std::shared_ptr<const EventHandler>;
+using SharedEventTarget = std::shared_ptr<const EventTarget>;
+using WeakEventTarget = std::weak_ptr<const EventTarget>;
 
-/*
- * EmptyEventTarget is used when some event cannot be dispatched to an original
- * event target but still has to be dispatched to preserve consistency of event flow.
- */
-static const EventTarget EmptyEventTarget = nullptr;
-
-using EventPipe = std::function<void(const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload)>;
+using EventPipe = std::function<void(const EventTarget *eventTarget, const std::string &type, const folly::dynamic &payload)>;
 
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/uimanager/FabricUIManager.cpp

@@ -105,20 +105,15 @@ void FabricUIManager::setDispatchEventToTargetFunction(std::function<DispatchEve
   dispatchEventToTargetFunction_ = dispatchEventFunction;
 }
 
-void FabricUIManager::setReleaseEventTargetFunction(std::function<ReleaseEventTargetFunction> releaseEventTargetFunction) {
-  releaseEventTargetFunction_ = releaseEventTargetFunction;
-}
-
-void FabricUIManager::dispatchEventToTarget(const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload) const {
-  if (eventTarget != EmptyEventTarget) {
+void FabricUIManager::dispatchEventToTarget(const EventTarget *eventTarget, const std::string &type, const folly::dynamic &payload) const {
+  if (eventTarget) {
     dispatchEventToTargetFunction_(
       *eventHandler_,
-      eventTarget,
+      *eventTarget,
       const_cast<std::string &>(type),
       const_cast<folly::dynamic &>(payload)
     );
-  }
-  else {
+  } else {
     dispatchEventToEmptyTargetFunction_(
       *eventHandler_,
       const_cast<std::string &>(type),
@@ -127,11 +122,7 @@ void FabricUIManager::dispatchEventToTarget(const EventTarget &eventTarget, cons
   }
 }
 
-void FabricUIManager::releaseEventTarget(const EventTarget &eventTarget) const {
-  releaseEventTargetFunction_(eventTarget);
-}
-
-SharedShadowNode FabricUIManager::createNode(int tag, std::string viewName, int rootTag, folly::dynamic props, EventTarget eventTarget) {
+SharedShadowNode FabricUIManager::createNode(int tag, std::string viewName, int rootTag, folly::dynamic props, SharedEventTarget eventTarget) {
   isLoggingEnabled && LOG(INFO) << "FabricUIManager::createNode(tag: " << tag << ", name: " << viewName << ", rootTag: " << rootTag << ", props: " << props << ")";
 
   ComponentName componentName = componentNameByReactViewName(viewName);
@@ -142,7 +133,7 @@ SharedShadowNode FabricUIManager::createNode(int tag, std::string viewName, int
     componentDescriptor->createShadowNode({
       .tag = tag,
       .rootTag = rootTag,
-      .eventEmitter = componentDescriptor->createEventEmitter(eventTarget, tag),
+      .eventEmitter = componentDescriptor->createEventEmitter(std::move(eventTarget), tag),
       .props = componentDescriptor->cloneProps(nullptr, rawProps)
     });
 
@@ -246,7 +237,7 @@ void FabricUIManager::completeRoot(int rootTag, const SharedShadowNodeUnsharedLi
 
 void FabricUIManager::registerEventHandler(std::shared_ptr<EventHandler> eventHandler) {
   isLoggingEnabled && LOG(INFO) << "FabricUIManager::registerEventHandler(eventHandler: " << eventHandler.get() << ")";
-  eventHandler_ = eventHandler;
+  eventHandler_ = std::move(eventHandler);
 }
 
 } // namespace react

ReactCommon/fabric/uimanager/FabricUIManager.h

@@ -19,7 +19,7 @@ namespace facebook {
 namespace react {
 
 using DispatchEventToEmptyTargetFunction = void (const EventHandler &eventHandler, std::string type, folly::dynamic payload);
-using DispatchEventToTargetFunction = void (const EventHandler &eventHandler, EventTarget eventTarget, std::string type, folly::dynamic payload);
+using DispatchEventToTargetFunction = void (const EventHandler &eventHandler, const EventTarget &eventTarget, std::string type, folly::dynamic payload);
 using ReleaseEventTargetFunction = void (EventTarget eventTarget);
 
 class FabricUIManager {
@@ -44,16 +44,14 @@ public:
    */
   void setDispatchEventToEmptyTargetFunction(std::function<DispatchEventToEmptyTargetFunction> dispatchEventFunction);
   void setDispatchEventToTargetFunction(std::function<DispatchEventToTargetFunction> dispatchEventFunction);
-  void setReleaseEventTargetFunction(std::function<ReleaseEventTargetFunction> releaseEventTargetFunction);
 
 #pragma mark - Native-facing Interface
 
-  void dispatchEventToTarget(const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload) const;
-  void releaseEventTarget(const EventTarget &eventTarget) const;
+  void dispatchEventToTarget(const EventTarget *eventTarget, const std::string &type, const folly::dynamic &payload) const;
 
 #pragma mark - JavaScript/React-facing Interface
 
-  SharedShadowNode createNode(Tag reactTag, std::string viewName, Tag rootTag, folly::dynamic props, EventTarget eventTarget);
+  SharedShadowNode createNode(Tag reactTag, std::string viewName, Tag rootTag, folly::dynamic props, SharedEventTarget eventTarget);
   SharedShadowNode cloneNode(const SharedShadowNode &node);
   SharedShadowNode cloneNodeWithNewChildren(const SharedShadowNode &node);
   SharedShadowNode cloneNodeWithNewProps(const SharedShadowNode &node, folly::dynamic props);
@@ -71,7 +69,6 @@ private:
   std::shared_ptr<EventHandler> eventHandler_;
   std::function<DispatchEventToEmptyTargetFunction> dispatchEventToEmptyTargetFunction_;
   std::function<DispatchEventToTargetFunction> dispatchEventToTargetFunction_;
-  std::function<ReleaseEventTargetFunction> releaseEventTargetFunction_;
 };
 
 } // namespace react

ReactCommon/fabric/uimanager/ShadowTree.cpp

@@ -18,7 +18,7 @@ namespace react {
 ShadowTree::ShadowTree(Tag rootTag):
   rootTag_(rootTag) {
 
-  const auto noopEventEmitter = std::make_shared<const ViewEventEmitter>(nullptr, rootTag, nullptr);
+  const auto noopEventEmitter = std::make_shared<const ViewEventEmitter>(nullptr, rootTag, std::shared_ptr<const EventDispatcher>());
   rootShadowNode_ = std::make_shared<RootShadowNode>(
     ShadowNodeFragment {
       .tag = rootTag,
@@ -30,6 +30,10 @@ ShadowTree::ShadowTree(Tag rootTag):
   );
 }
 
+ShadowTree::~ShadowTree() {
+  complete(std::make_shared<SharedShadowNodeList>(SharedShadowNodeList {}));
+}
+
 Tag ShadowTree::getRootTag() const {
   return rootTag_;
 }

ReactCommon/fabric/uimanager/ShadowTree.h

@@ -30,6 +30,8 @@ public:
    */
   ShadowTree(Tag rootTag);
 
+  ~ShadowTree();
+
   /*
    * Returns the rootTag associated with the shadow tree (the tag of the
    * root shadow node).