Fix race condition in backlight adjustment.

When configuring the automatic backlight levels, there's a race
condition in setting the lux and brightness settings as the settings
provider doesn't allow storing multiple settings atomically. When
deleting rows, there's quite a high chance of DisplayPowerController
picking up a state where the lux values already have the lower number of
rows, but the brightness values do not, effectively leading to an
ArrayIndexOutOfBoundsException.

Fix that by
- waiting a second of cool-down time until applying the settings and
- adding a sanity check for the very unlikely case that the delay
  between writing both values is > 1 second

Change-Id: I44e41530fc5334aaefc4ab7d3a90542f78fabe0c
JIRA:CYAN-755
Signed-off-by: DHO <DHO@dho.im>

Conflicts:

	services/java/com/android/server/power/DisplayPowerController.java

services/java/com/android/server/power/DisplayPowerController.java

@@ -112,6 +112,7 @@ final class DisplayPowerController {
     private static final int MSG_UPDATE_POWER_STATE = 1;
     private static final int MSG_PROXIMITY_SENSOR_DEBOUNCED = 2;
     private static final int MSG_LIGHT_SENSOR_DEBOUNCED = 3;
+    private static final int MSG_UPDATE_BACKLIGHT_SETTINGS = 4;
 
     private static final int PROXIMITY_UNKNOWN = -1;
     private static final int PROXIMITY_NEGATIVE = 0;
@@ -371,10 +372,17 @@ public DisplayPowerController(Looper looper, Context context, Notifier notifier,
         mUseSoftwareAutoBrightnessConfig = resources.getBoolean(
                 com.android.internal.R.bool.config_automatic_brightness_available);
         if (mUseSoftwareAutoBrightnessConfig) {
-            int[] lux = resources.getIntArray(
-                    com.android.internal.R.array.config_autoBrightnessLevels);
-            int[] screenBrightness = resources.getIntArray(
-                    com.android.internal.R.array.config_autoBrightnessLcdBacklightValues);
+            final ContentResolver cr = mContext.getContentResolver();
+            final ContentObserver observer = new ContentObserver(mHandler) {
+                @Override
+                public void onChange(boolean selfChange, Uri uri) {
+                    // As both LUX and BACKLIGHT might be changed at the same time, there's
+                    // a potential race condition. As the settings provider API doesn't give
+                    // us transactions to avoid them, wait a little until things settle down
+                    mHandler.removeMessages(MSG_UPDATE_BACKLIGHT_SETTINGS);
+                    mHandler.sendEmptyMessageDelayed(MSG_UPDATE_BACKLIGHT_SETTINGS, 1000);
+                }
+            };
 
             mScreenAutoBrightnessSpline = createAutoBrightnessSpline(lux, screenBrightness);
             if (mScreenAutoBrightnessSpline == null) {
@@ -420,6 +428,10 @@ public DisplayPowerController(Looper looper, Context context, Notifier notifier,
     }
 
     private static Spline createAutoBrightnessSpline(int[] lux, int[] brightness) {
+        if (lux.length < 2 || lux.length != (brightness.length - 1)) {
+            return null;
+        }
+
         try {
             final int n = brightness.length;
             float[] x = new float[n];
@@ -1281,6 +1293,12 @@ public void handleMessage(Message msg) {
                 case MSG_LIGHT_SENSOR_DEBOUNCED:
                     debounceLightSensor();
                     break;
+
+                case MSG_UPDATE_BACKLIGHT_SETTINGS:
+                    mAutoBrightnessSettingsChanged = true;
+                    updateAutomaticBrightnessSettings();
+                    updatePowerState();
+                    break;
             }
         }
     }