From 894ee722787b18cf2fdfc657781c917c737d37d8 Mon Sep 17 00:00:00 2001
From: David Vacca <dvacca@fb.com>
Date: Sun, 3 Nov 2019 14:52:18 -0800
Subject: [PATCH] Collapse Delete-Create mounting instructions

Summary:
This diff implements an optimization / fix in the mounting layer of Fabric Android to ignore the "deletion" and "creation" of views for the same tag in the same commit.
This operation is adding ~100 ns for every commit (I measured this using a release APK running in a real device). I created a QE to enable / disable this optimization and to measure the performance impact of this change in production

Changelog: Implement optimization in mounting layer of Fabric

Reviewed By: JoshuaGross

Differential Revision: D18279240

fbshipit-source-id: d6fdeb2a9676bcfaf47886893eed5024bf86204b
---
 .../java/com/facebook/react/fabric/jni/BUCK   |  1 +
 .../com/facebook/react/fabric/jni/Binding.cpp | 24 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/BUCK b/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/BUCK
index 75b75835b3b..a804631c65a 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/BUCK
+++ b/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/BUCK
@@ -26,6 +26,7 @@ rn_xplat_cxx_library(
     soname = "libfabricjni.$(ext)",
     visibility = ["PUBLIC"],
     deps = [
+        react_native_xplat_target("better:better"),
         react_native_xplat_target("config:config"),
         react_native_xplat_target("fabric/uimanager:uimanager"),
         react_native_xplat_target("fabric/components/scrollview:scrollview"),
diff --git a/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/Binding.cpp b/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/Binding.cpp
index ef67cc68163..e47befe09cc 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/Binding.cpp
+++ b/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/Binding.cpp
@@ -11,6 +11,7 @@
 #include "ReactNativeConfigHolder.h"
 #include "StateWrapperImpl.h"
 
+#import <better/set.h>
 #include <fb/fbjni.h>
 #include <jsi/JSIDynamic.h>
 #include <jsi/jsi.h>
@@ -572,6 +573,21 @@ void Binding::schedulerDidFinishTransaction(
   auto surfaceId = mountingTransaction->getSurfaceId();
   auto &mutations = mountingTransaction->getMutations();
 
+  facebook::better::set<int> createAndDeleteTagsToProcess;
+  if (collapseDeleteCreateMountingInstructions_) {
+    for (const auto &mutation : mutations) {
+      if (mutation.type == ShadowViewMutation::Delete) {
+        createAndDeleteTagsToProcess.insert(mutation.oldChildShadowView.tag);
+      } else if (mutation.type == ShadowViewMutation::Create) {
+        int tag = mutation.oldChildShadowView.tag;
+        if (createAndDeleteTagsToProcess.find(tag) != createAndDeleteTagsToProcess.end()) {
+          createAndDeleteTagsToProcess.erase(tag);
+        } else {
+          createAndDeleteTagsToProcess.insert(tag);
+        }
+      }
+    }
+  }
   int64_t commitNumber = telemetry.getCommitNumber();
 
   std::vector<local_ref<jobject>> queue;
@@ -591,6 +607,14 @@ void Binding::schedulerDidFinishTransaction(
   for (const auto &mutation : mutations) {
     auto oldChildShadowView = mutation.oldChildShadowView;
     auto newChildShadowView = mutation.newChildShadowView;
+    auto mutationType = mutation.type;
+
+    if (collapseDeleteCreateMountingInstructions_ &&
+        (mutationType == ShadowViewMutation::Create || mutationType == ShadowViewMutation::Delete) &&
+        createAndDeleteTagsToProcess.size() > 0 &&
+        createAndDeleteTagsToProcess.find(mutation.newChildShadowView.tag) == createAndDeleteTagsToProcess.end())  {
+      continue;
+    }
 
     bool isVirtual = newChildShadowView.layoutMetrics == EmptyLayoutMetrics &&
         oldChildShadowView.layoutMetrics == EmptyLayoutMetrics;