Allow events recycling and implement recyclable OnLayoutEvents.

Differential Revision: D2585530

fb-gh-sync-id: cb671e39fd64c27a9c11e3cd064bd19cabe7f3b6

ReactAndroid/src/main/java/com/facebook/react/uimanager/OnLayoutEvent.java

@@ -9,6 +9,9 @@
 
 package com.facebook.react.uimanager;
 
+import android.os.SystemClock;
+import android.support.v4.util.Pools;
+
 import com.facebook.react.bridge.Arguments;
 import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.uimanager.events.Event;
@@ -19,10 +22,30 @@ import com.facebook.react.uimanager.events.RCTEventEmitter;
  */
 /* package */ class OnLayoutEvent extends Event<OnLayoutEvent> {
 
-  private final int mX, mY, mWidth, mHeight;
+  private static final Pools.SynchronizedPool<OnLayoutEvent> EVENTS_POOL =
+      new Pools.SynchronizedPool<>(20);
 
-  protected OnLayoutEvent(int viewTag, int x, int y, int width, int height) {
+  private int mX, mY, mWidth, mHeight;
-    super(viewTag, 0);
+
+  public static OnLayoutEvent obtain(int viewTag, int x, int y, int width, int height) {
+    OnLayoutEvent event = EVENTS_POOL.acquire();
+    if (event == null) {
+      event = new OnLayoutEvent();
+    }
+    event.init(viewTag, x, y, width, height);
+    return event;
+  }
+
+  @Override
+  public void onDispose() {
+    EVENTS_POOL.release(this);
+  }
+
+  private OnLayoutEvent() {
+  }
+
+  protected void init(int viewTag, int x, int y, int width, int height) {
+    super.init(viewTag, SystemClock.uptimeMillis());
     mX = x;
     mY = y;
     mWidth = width;

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModule.java

@@ -806,7 +806,7 @@ public class UIManagerModule extends ReactContextBaseJavaModule implements
       // notify JS about layout event if requested
       if (cssNode.shouldNotifyOnLayout()) {
         mEventDispatcher.dispatchEvent(
-            new OnLayoutEvent(
+            OnLayoutEvent.obtain(
                 tag,
                 cssNode.getScreenX(),
                 cssNode.getScreenY(),

ReactAndroid/src/main/java/com/facebook/react/uimanager/events/Event.java

@@ -11,15 +11,31 @@ package com.facebook.react.uimanager.events;
 
 /**
  * A UI event that can be dispatched to JS.
+ *
+ * For dispatching events {@link EventDispatcher#dispatchEvent} should be used. Once event object
+ * is passed to the EventDispatched it should no longer be used as EventDispatcher may decide
+ * to recycle that object (by calling {@link #dispose}).
  */
 public abstract class Event<T extends Event> {
 
-  private final int mViewTag;
+  private boolean mInitialized;
-  private final long mTimestampMs;
+  private int mViewTag;
+  private long mTimestampMs;
+
+  protected Event() {
+  }
 
   protected Event(int viewTag, long timestampMs) {
+    init(viewTag, timestampMs);
+  }
+
+  /**
+   * This method needs to be called before event is sent to event dispatcher.
+   */
+  protected void init(int viewTag, long timestampMs) {
     mViewTag = viewTag;
     mTimestampMs = timestampMs;
+    mInitialized = true;
   }
 
   /**
@@ -68,7 +84,16 @@ public abstract class Event<T extends Event> {
    * Called when the EventDispatcher is done with an event, either because it was dispatched or
    * because it was coalesced with another Event.
    */
-  public void dispose() {
+  public void onDispose() {
+  }
+
+  /*package*/ boolean isInitialized() {
+    return mInitialized;
+  }
+
+  /*package*/ final void dispose() {
+    mInitialized = false;
+    onDispose();
   }
 
   /**

ReactAndroid/src/main/java/com/facebook/react/uimanager/events/EventDispatcher.java

@@ -110,6 +110,7 @@ public class EventDispatcher implements LifecycleEventListener {
    * Sends the given Event to JS, coalescing eligible events if JS is backed up.
    */
   public void dispatchEvent(Event event) {
+    Assertions.assertCondition(event.isInitialized(), "Dispatched event hasn't been initialized");
     synchronized (mEventsStagingLock) {
       mEventStaging.add(event);
     }

ReactAndroid/src/main/java/com/facebook/react/uimanager/events/TouchEvent.java

@@ -96,7 +96,7 @@ public class TouchEvent extends Event<TouchEvent> {
   }
 
   @Override
-  public void dispose() {
+  public void onDispose() {
     mMotionEvent.recycle();
   }
 }