From 90e2f37790afb51f35619f5024976688b98aae5d Mon Sep 17 00:00:00 2001
From: Philip Junker <philipjunker@google.com>
Date: Wed, 5 Oct 2022 16:25:17 +0200
Subject: [PATCH] Initialize ContentObserver in startObserving().

This removes a race condition where ContentObserver is initialized
while mHandler is null which causes the ContentObserver#onChange() callback to run on a different thread and can cause an NPE.

Bug: 246843362
Test: manual
Test: atest BrightnessSynchronizerTest
Change-Id: Ib8e192c3961390ece721fa473d5c09323c30bafe
---
 .../display/BrightnessSynchronizer.java       | 33 ++++++++++---------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/core/java/com/android/internal/display/BrightnessSynchronizer.java b/core/java/com/android/internal/display/BrightnessSynchronizer.java
index 627631a376f7f..d503904c2e3ca 100644
--- a/core/java/com/android/internal/display/BrightnessSynchronizer.java
+++ b/core/java/com/android/internal/display/BrightnessSynchronizer.java
@@ -115,7 +115,7 @@ public class BrightnessSynchronizer {
             Slog.i(TAG, "Setting initial brightness to default value of: " + defaultBrightness);
         }
 
-        mBrightnessSyncObserver.startObserving();
+        mBrightnessSyncObserver.startObserving(mHandler);
         mHandler.sendEmptyMessageAtTime(MSG_RUN_UPDATE, mClock.uptimeMillis());
     }
 
@@ -482,30 +482,31 @@ public class BrightnessSynchronizer {
             }
         };
 
-        private final ContentObserver mContentObserver = new ContentObserver(mHandler) {
-            @Override
-            public void onChange(boolean selfChange, Uri uri) {
-                if (selfChange) {
-                    return;
+        private ContentObserver createBrightnessContentObserver(Handler handler) {
+            return new ContentObserver(handler) {
+                @Override
+                public void onChange(boolean selfChange, Uri uri) {
+                    if (selfChange) {
+                        return;
+                    }
+                    if (BRIGHTNESS_URI.equals(uri)) {
+                        handleBrightnessChangeInt(getScreenBrightnessInt());
+                    }
                 }
-                if (BRIGHTNESS_URI.equals(uri)) {
-                    handleBrightnessChangeInt(getScreenBrightnessInt());
-                }
-            }
-        };
+            };
+        }
 
         boolean isObserving() {
             return mIsObserving;
         }
 
-        void startObserving() {
+        void startObserving(Handler handler) {
             final ContentResolver cr = mContext.getContentResolver();
-            cr.registerContentObserver(BRIGHTNESS_URI, false, mContentObserver,
-                    UserHandle.USER_ALL);
-            mDisplayManager.registerDisplayListener(mListener, mHandler,
+            cr.registerContentObserver(BRIGHTNESS_URI, false,
+                    createBrightnessContentObserver(handler), UserHandle.USER_ALL);
+            mDisplayManager.registerDisplayListener(mListener, handler,
                     DisplayManager.EVENT_FLAG_DISPLAY_BRIGHTNESS);
             mIsObserving = true;
         }
-
     }
 }