From c8f571fdad9d632ab618d53520b4365d4e464423 Mon Sep 17 00:00:00 2001
From: Joshua Gross <joshuagross@fb.com>
Date: Tue, 4 Aug 2020 17:10:41 -0700
Subject: [PATCH] Build ViewGroup mechanism for repeatedly retrying UpdateState
 until it succeeds

Summary:
With BackgroundExecutor+State Reconciliation, it is pretty common to have races where View layer UpdateState calls are thrown away.

Theoretically this is /always/ possible since C++ doesn't retry failed UpdateStates, we just try once and then bail. This is part 1 of improving our mechanisms for ensuring that State stays up-to-date from the View layer.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D22933927

fbshipit-source-id: 77b3b87402f772e3f149be0f9200e673bbed7b57
---
 .../react/config/ReactFeatureFlags.java       |  3 +
 .../uimanager/FabricStateBaseViewGroup.java   | 73 +++++++++++++++++++
 2 files changed, 76 insertions(+)
 create mode 100644 ReactAndroid/src/main/java/com/facebook/react/uimanager/FabricStateBaseViewGroup.java

diff --git a/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java b/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
index acea75b442f4db..7a6b8a95ae4c41 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
@@ -68,4 +68,7 @@ public class ReactFeatureFlags {
 
   /** Feature flag to use stopSurface when ReactRootView is unmounted. */
   public static boolean enableStopSurfaceOnRootViewUnmount = false;
+
+  /** Use experimental SetState retry mechanism in view? */
+  public static boolean enableExperimentalStateUpdateRetry = false;
 }
diff --git a/ReactAndroid/src/main/java/com/facebook/react/uimanager/FabricStateBaseViewGroup.java b/ReactAndroid/src/main/java/com/facebook/react/uimanager/FabricStateBaseViewGroup.java
new file mode 100644
index 00000000000000..af24da786bce3a
--- /dev/null
+++ b/ReactAndroid/src/main/java/com/facebook/react/uimanager/FabricStateBaseViewGroup.java
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.uimanager;
+
+import android.view.ViewGroup;
+import com.facebook.react.bridge.UiThreadUtil;
+import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.config.ReactFeatureFlags;
+
+/** This is a helper base class for ViewGroups that use Fabric State. */
+public abstract class FabricStateBaseViewGroup extends ViewGroup {
+  public interface StateUpdateCallback {
+    WritableMap getStateUpdate();
+  }
+
+  private StateWrapper mStateWrapper = null;
+
+  public FabricStateBaseViewGroup(ThemedReactContext context) {
+    super(context);
+  }
+
+  public void setStateWrapper(StateWrapper stateWrapper) {
+    mStateWrapper = stateWrapper;
+  }
+
+  private static void setState(
+      final FabricStateBaseViewGroup view,
+      final StateWrapper stateWrapper,
+      final StateUpdateCallback stateUpdateCallback,
+      final int numTries) {
+    // The StateWrapper will change, breaking this loop, whenever the UpdateState MountItem
+    // is executed.
+    // The caller is responsible for detecting if data is up-to-date, and doing nothing, or
+    // detecting if state is stale and calling setState again.
+    if (stateWrapper != view.mStateWrapper) {
+      return;
+    }
+    // We arbitrarily bail out after a certain number of retries.
+    // This is a pretty large number: in practice I've seen this number go over 50
+    // with minimal/no visual jank.
+    if (numTries > 5 * 60) {
+      return;
+    }
+
+    stateWrapper.updateState(stateUpdateCallback.getStateUpdate());
+
+    // An `updateState` call can fail, and there's no way to verify if it succeeds besides
+    // waiting for a corresponding `StateUpdate` MountItem to be executed on some future UI tick.
+    // So.... to resolve conflicts with updateState, we just keep firing it until it succeeds or
+    // the View goes away.
+    if (ReactFeatureFlags.enableExperimentalStateUpdateRetry) {
+      UiThreadUtil.runOnUiThread(
+          new Runnable() {
+            @Override
+            public void run() {
+              setState(view, stateWrapper, stateUpdateCallback, numTries + 1);
+            }
+          });
+    }
+  }
+
+  public static void setState(
+      final FabricStateBaseViewGroup view,
+      final StateWrapper stateWrapper,
+      final StateUpdateCallback stateUpdateCallback) {
+    setState(view, stateWrapper, stateUpdateCallback, 0);
+  }
+}