From b49c8add15d181240be43e02f97330b979a0e72d Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Mon, 27 Aug 2018 07:21:24 -0700
Subject: [PATCH] Fabric: Rethinking of EventEmitter's role

Summary:
@public
Now, one of the main purposes of `EventEmitter`s is to create RawEvent instances for all specific event invocations.

Reviewed By: mdvacca

Differential Revision: D8886226

fbshipit-source-id: 82a489174efcda097887e70650a2038dc986d149
---
 ReactCommon/fabric/events/EventEmitter.cpp | 59 +++++++++++++++++-----
 ReactCommon/fabric/events/EventEmitter.h   | 23 ++++++---
 2 files changed, 61 insertions(+), 21 deletions(-)

diff --git a/ReactCommon/fabric/events/EventEmitter.cpp b/ReactCommon/fabric/events/EventEmitter.cpp
index 2e99199ee..46d6cb064 100644
--- a/ReactCommon/fabric/events/EventEmitter.cpp
+++ b/ReactCommon/fabric/events/EventEmitter.cpp
@@ -9,22 +9,33 @@
 
 #include <folly/dynamic.h>
 
+#include "RawEvent.h"
+
 namespace facebook {
 namespace react {
 
-EventEmitter::EventEmitter(const EventTarget &eventTarget, const Tag &tag, const SharedEventDispatcher &eventDispatcher):
-  eventTarget_(eventTarget),
-  tag_(tag),
-  eventDispatcher_(eventDispatcher) {
+// TODO(T29874519): Get rid of "top" prefix once and for all.
+/*
+ * Capitalizes the first letter of the event type and adds "top" prefix
+ * (e.g. "layout" becames "topLayout").
+ */
+static std::string normalizeEventType(const std::string &type) {
+  std::string prefixedType = type;
+  prefixedType[0] = toupper(prefixedType[0]);
+  prefixedType.insert(0, "top");
+  return prefixedType;
 }
 
-EventEmitter::~EventEmitter() {
-  auto &&eventDispatcher = eventDispatcher_.lock();
-  if (eventDispatcher && eventTarget_) {
-    eventDispatcher->releaseEventTarget(eventTarget_);
-  }
+std::recursive_mutex &EventEmitter::DispatchMutex() {
+  static std::recursive_mutex mutex;
+  return mutex;
 }
 
+EventEmitter::EventEmitter(const EventTarget &eventTarget, const Tag &tag, const std::shared_ptr<const EventDispatcher> &eventDispatcher):
+  eventTarget_(eventTarget),
+  tag_(tag),
+  eventDispatcher_(eventDispatcher) {}
+
 void EventEmitter::dispatchEvent(
   const std::string &type,
   const folly::dynamic &payload,
@@ -35,15 +46,37 @@ void EventEmitter::dispatchEvent(
     return;
   }
 
-  assert(eventTarget_ && "Attempted to dispatch an event without an eventTarget.");
-
   // Mixing `target` into `payload`.
   assert(payload.isObject());
   folly::dynamic extendedPayload = folly::dynamic::object("target", tag_);
   extendedPayload.merge_patch(payload);
 
-  // TODO(T29610783): Reconsider using dynamic dispatch here.
-  eventDispatcher->dispatchEvent(eventTarget_, type, extendedPayload, priority);
+  std::weak_ptr<const EventEmitter> weakEventEmitter = shared_from_this();
+
+  eventDispatcher->dispatchEvent(
+    RawEvent(
+      normalizeEventType(type),
+      extendedPayload,
+      eventTarget_,
+      [weakEventEmitter]() {
+        auto eventEmitter = weakEventEmitter.lock();
+        if (!eventEmitter) {
+          return false;
+        }
+
+        return eventEmitter->getEnabled();
+      }
+    ),
+    priority
+  );
+}
+
+void EventEmitter::setEnabled(bool enabled) const {
+  enabled_ = enabled;
+}
+
+bool EventEmitter::getEnabled() const {
+  return enabled_;
 }
 
 } // namespace react
diff --git a/ReactCommon/fabric/events/EventEmitter.h b/ReactCommon/fabric/events/EventEmitter.h
index f2f41732e..01694e520 100644
--- a/ReactCommon/fabric/events/EventEmitter.h
+++ b/ReactCommon/fabric/events/EventEmitter.h
@@ -24,10 +24,9 @@ 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.
- *
- * TODO: Reconsider naming of all event-related things.
  */
-class EventEmitter {
+class EventEmitter:
+  public std::enable_shared_from_this<EventEmitter> {
 
   /*
    * We have to repeat `Tag` type definition here because `events` module does
@@ -36,11 +35,19 @@ class EventEmitter {
   using Tag = int32_t;
 
 public:
-  EventEmitter(const EventTarget &eventTarget, const Tag &tag, const SharedEventDispatcher &eventDispatcher);
-  virtual ~EventEmitter();
+  static std::recursive_mutex &DispatchMutex();
+
+  EventEmitter(const EventTarget &eventTarget, const Tag &tag, const std::shared_ptr<const EventDispatcher> &eventDispatcher);
+  virtual ~EventEmitter() = default;
+
+  /*
+   * Indicates that an event can be delivered to `eventTarget`.
+   * Callsite must acquire `DispatchMutex` to access those methods.
+   */
+  void setEnabled(bool enabled) const;
+  bool getEnabled() const;
 
 protected:
-
   /*
    * Initates an event delivery process.
    * Is used by particular subclasses only.
@@ -52,10 +59,10 @@ protected:
   ) const;
 
 private:
-
-  mutable EventTarget eventTarget_ {nullptr};
+  EventTarget eventTarget_;
   Tag tag_;
   std::weak_ptr<const EventDispatcher> eventDispatcher_;
+  mutable bool enabled_; // Protected by `DispatchMutex`.
 };
 
 } // namespace react