Avoid string copy in event dispatching

Summary:
Changelog: [internal]

To avoid unnecessary string copy in event pipeline, use move semantics.

Event pipeline has ownership of event type. Passing it by reference ends up in a copy when `RawEvent` object is constructed. To avoid this, pass string by value through each layer and use move semantics to avoid extra copies.

Reviewed By: javache

Differential Revision: D34392608

fbshipit-source-id: c11d221be345665e165d9edbc360ba5a057e3890

ReactAndroid/src/main/java/com/facebook/react/fabric/jni/EventEmitterWrapper.cpp

@@ -19,7 +19,7 @@ EventEmitterWrapper::initHybrid(jni::alias_ref<jclass>) {
 }
 
 void EventEmitterWrapper::invokeEvent(
-    std::string const &eventName,
+    std::string eventName,
     NativeMap *payload,
     int category) {
   // It is marginal, but possible for this to be constructed without a valid
@@ -35,7 +35,7 @@ void EventEmitterWrapper::invokeEvent(
 }
 
 void EventEmitterWrapper::invokeUniqueEvent(
-    std::string const &eventName,
+    std::string eventName,
     NativeMap *payload,
     int customCoalesceKey) {
   // TODO: customCoalesceKey currently unused

ReactAndroid/src/main/java/com/facebook/react/fabric/jni/EventEmitterWrapper.h

@@ -25,10 +25,9 @@ class EventEmitterWrapper : public jni::HybridClass<EventEmitterWrapper> {
 
   SharedEventEmitter eventEmitter;
 
-  void
-  invokeEvent(std::string const &eventName, NativeMap *params, int category);
+  void invokeEvent(std::string eventName, NativeMap *params, int category);
   void invokeUniqueEvent(
-      std::string const &eventName,
+      std::string eventName,
       NativeMap *params,
       int customCoalesceKey);
 

ReactCommon/react/renderer/components/scrollview/ScrollViewEventEmitter.cpp

@@ -86,11 +86,11 @@ void ScrollViewEventEmitter::onMomentumScrollEnd(
 }
 
 void ScrollViewEventEmitter::dispatchScrollViewEvent(
-    const std::string &name,
+    std::string name,
     const ScrollViewMetrics &scrollViewMetrics,
     EventPriority priority) const {
   dispatchEvent(
-      name,
+      std::move(name),
       [scrollViewMetrics](jsi::Runtime &runtime) {
         return scrollViewMetricsPayload(runtime, scrollViewMetrics);
       },

ReactCommon/react/renderer/components/scrollview/ScrollViewEventEmitter.h

@@ -38,7 +38,7 @@ class ScrollViewEventEmitter : public ViewEventEmitter {
 
  private:
   void dispatchScrollViewEvent(
-      const std::string &name,
+      std::string name,
       const ScrollViewMetrics &scrollViewMetrics,
       EventPriority priority = EventPriority::AsynchronousBatched) const;
 };

ReactCommon/react/renderer/components/view/TouchEventEmitter.cpp

@@ -60,12 +60,12 @@ static jsi::Value touchEventPayload(
 }
 
 void TouchEventEmitter::dispatchTouchEvent(
-    std::string const &type,
+    std::string type,
     TouchEvent const &event,
     EventPriority priority,
     RawEvent::Category category) const {
   dispatchEvent(
-      type,
+      std::move(type),
       [event](jsi::Runtime &runtime) {
         return touchEventPayload(runtime, event);
       },

ReactCommon/react/renderer/components/view/TouchEventEmitter.h

@@ -31,7 +31,7 @@ class TouchEventEmitter : public EventEmitter {
 
  private:
   void dispatchTouchEvent(
-      std::string const &type,
+      std::string type,
       TouchEvent const &event,
       EventPriority priority,
       RawEvent::Category category) const;

ReactCommon/react/renderer/components/view/ViewEventEmitter.cpp

@@ -12,7 +12,7 @@ namespace react {
 
 #pragma mark - Accessibility
 
-void ViewEventEmitter::onAccessibilityAction(const std::string &name) const {
+void ViewEventEmitter::onAccessibilityAction(std::string const &name) const {
   dispatchEvent("accessibilityAction", [name](jsi::Runtime &runtime) {
     auto payload = jsi::Object(runtime);
     payload.setProperty(runtime, "actionName", name);

ReactCommon/react/renderer/components/view/ViewEventEmitter.h

@@ -28,7 +28,7 @@ class ViewEventEmitter : public TouchEventEmitter {
 
 #pragma mark - Accessibility
 
-  void onAccessibilityAction(const std::string &name) const;
+  void onAccessibilityAction(std::string const &name) const;
   void onAccessibilityTap() const;
   void onAccessibilityMagicTap() const;
   void onAccessibilityEscape() const;

ReactCommon/react/renderer/core/EventEmitter.cpp

@@ -22,9 +22,9 @@ namespace react {
  * Capitalizes the first letter of the event type and adds "top" prefix if
  * necessary (e.g. "layout" becames "topLayout").
  */
-static std::string normalizeEventType(const std::string &type) {
-  auto prefixedType = type;
-  if (type.find("top", 0) != 0) {
+static std::string normalizeEventType(std::string type) {
+  auto prefixedType = std::move(type);
+  if (prefixedType.find("top", 0) != 0) {
     prefixedType.insert(0, "top");
     prefixedType[3] = static_cast<char>(toupper(prefixedType[3]));
   }
@@ -50,12 +50,12 @@ EventEmitter::EventEmitter(
       eventDispatcher_(std::move(eventDispatcher)) {}
 
 void EventEmitter::dispatchEvent(
-    const std::string &type,
+    std::string type,
     const folly::dynamic &payload,
     EventPriority priority,
     RawEvent::Category category) const {
   dispatchEvent(
-      type,
+      std::move(type),
       [payload](jsi::Runtime &runtime) {
         return valueFromDynamic(runtime, payload);
       },
@@ -64,15 +64,15 @@ void EventEmitter::dispatchEvent(
 }
 
 void EventEmitter::dispatchUniqueEvent(
-    const std::string &type,
+    std::string type,
     const folly::dynamic &payload) const {
-  dispatchUniqueEvent(type, [payload](jsi::Runtime &runtime) {
+  dispatchUniqueEvent(std::move(type), [payload](jsi::Runtime &runtime) {
     return valueFromDynamic(runtime, payload);
   });
 }
 
 void EventEmitter::dispatchEvent(
-    const std::string &type,
+    std::string type,
     const ValueFactory &payloadFactory,
     EventPriority priority,
     RawEvent::Category category) const {
@@ -85,12 +85,15 @@ void EventEmitter::dispatchEvent(
 
   eventDispatcher->dispatchEvent(
       RawEvent(
-          normalizeEventType(type), payloadFactory, eventTarget_, category),
+          normalizeEventType(std::move(type)),
+          payloadFactory,
+          eventTarget_,
+          category),
       priority);
 }
 
 void EventEmitter::dispatchUniqueEvent(
-    const std::string &type,
+    std::string type,
     const ValueFactory &payloadFactory) const {
   SystraceSection s("EventEmitter::dispatchUniqueEvent");
 
@@ -100,7 +103,7 @@ void EventEmitter::dispatchUniqueEvent(
   }
 
   eventDispatcher->dispatchUniqueEvent(RawEvent(
-      normalizeEventType(type),
+      normalizeEventType(std::move(type)),
       payloadFactory,
       eventTarget_,
       RawEvent::Category::Continuous));

ReactCommon/react/renderer/core/EventEmitter.h

@@ -68,24 +68,23 @@ class EventEmitter {
    * Is used by particular subclasses only.
    */
   void dispatchEvent(
-      const std::string &type,
+      std::string type,
       const ValueFactory &payloadFactory =
           EventEmitter::defaultPayloadFactory(),
       EventPriority priority = EventPriority::AsynchronousBatched,
       RawEvent::Category category = RawEvent::Category::Unspecified) const;
 
   void dispatchEvent(
-      const std::string &type,
+      std::string type,
       const folly::dynamic &payload,
       EventPriority priority = EventPriority::AsynchronousBatched,
       RawEvent::Category category = RawEvent::Category::Unspecified) const;
 
-  void dispatchUniqueEvent(
-      const std::string &type,
-      const folly::dynamic &payload) const;
+  void dispatchUniqueEvent(std::string type, const folly::dynamic &payload)
+      const;
 
   void dispatchUniqueEvent(
-      const std::string &type,
+      std::string type,
       const ValueFactory &payloadFactory =
           EventEmitter::defaultPayloadFactory()) const;