From 4655f2063d08a129ac141dbb0716c88a173ab586 Mon Sep 17 00:00:00 2001
From: Samuel Susla <samuelsusla@meta.com>
Date: Mon, 30 Oct 2023 07:42:24 -0700
Subject: [PATCH] add feature flag to disable Choreographer callbacks in Paper
 infra

Summary:
changelog: [internal]

For constrained environments, we want to lower cpu usage of RN when the app is idle. `UIViewOperationQueue` and `EventDispatcherImpl` are not used in Fabric and therefore they do not need to run on each frame.

Reviewed By: javache

Differential Revision: D50741161

fbshipit-source-id: aa605893f1c8a4ac97a49bb7a6de2e2637a0832e
---
 .../java/com/facebook/react/config/ReactFeatureFlags.java | 8 ++++++++
 .../facebook/react/uimanager/UIViewOperationQueue.java    | 7 +++++--
 .../react/uimanager/events/EventDispatcherImpl.java       | 8 ++++++--
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
index 366da86b585..c6b437257dd 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
@@ -174,4 +174,12 @@ public class ReactFeatureFlags {
    * in JS will be rejected (The JS error will include native stack)
    */
   public static boolean rejectTurboModulePromiseOnNativeError = true;
+
+  /*
+   * When the app is completely migrated to Fabric, set this flag to true to
+   * disable parts of Paper infrastructre that are not needed anymore but consume
+   * memory and CPU. Specifically, UIViewOperationQueue and EventDispatcherImpl will no
+   * longer work as they won't subscribe to ReactChoregrapher for updates.
+   */
+  public static boolean enableFabricRendererExclusively = false;
 }
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/UIViewOperationQueue.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/UIViewOperationQueue.java
index 73bb4ac0be2..13e37b48916 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/UIViewOperationQueue.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/UIViewOperationQueue.java
@@ -25,6 +25,7 @@ import com.facebook.react.bridge.RetryableMountingLayerException;
 import com.facebook.react.bridge.SoftAssertions;
 import com.facebook.react.bridge.UiThreadUtil;
 import com.facebook.react.common.ReactConstants;
+import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.modules.core.ReactChoreographer;
 import com.facebook.react.uimanager.debug.NotThreadSafeViewHierarchyUpdateDebugListener;
 import com.facebook.systrace.Systrace;
@@ -962,8 +963,10 @@ public class UIViewOperationQueue {
 
   /* package */ void resumeFrameCallback() {
     mIsDispatchUIFrameCallbackEnqueued = true;
-    ReactChoreographer.getInstance()
-        .postFrameCallback(ReactChoreographer.CallbackType.DISPATCH_UI, mDispatchUIFrameCallback);
+    if (!ReactFeatureFlags.enableFabricRendererExclusively) {
+      ReactChoreographer.getInstance()
+          .postFrameCallback(ReactChoreographer.CallbackType.DISPATCH_UI, mDispatchUIFrameCallback);
+    }
   }
 
   /* package */ void pauseFrameCallback() {
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/EventDispatcherImpl.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/EventDispatcherImpl.java
index 320b7df3a9b..91ec4d2e0fd 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/EventDispatcherImpl.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/EventDispatcherImpl.java
@@ -14,6 +14,7 @@ import com.facebook.react.bridge.LifecycleEventListener;
 import com.facebook.react.bridge.ReactApplicationContext;
 import com.facebook.react.bridge.UiThreadUtil;
 import com.facebook.react.common.MapBuilder;
+import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.modules.core.ReactChoreographer;
 import com.facebook.react.uimanager.common.UIManagerType;
 import com.facebook.systrace.Systrace;
@@ -315,8 +316,11 @@ public class EventDispatcherImpl implements EventDispatcher, LifecycleEventListe
     }
 
     private void post() {
-      ReactChoreographer.getInstance()
-          .postFrameCallback(ReactChoreographer.CallbackType.TIMERS_EVENTS, mCurrentFrameCallback);
+      if (!ReactFeatureFlags.enableFabricRendererExclusively) {
+        ReactChoreographer.getInstance()
+            .postFrameCallback(
+                ReactChoreographer.CallbackType.TIMERS_EVENTS, mCurrentFrameCallback);
+      }
     }
 
     public void maybePostFromNonUI() {