Fix a race in accessibility manager.

The accessibility manager has APIs for clients to observe changes
in accessibility, touch exploration, and high contrast states. The
notification of the listeners has to be done with no lock held but
in an attempt to do that the code was incorrectly iterating over
the copy on write collection.

bug:18840784

Change-Id: I6803ff1657fbf6b0cc7936671d5bbdebb5cbf6bb

core/java/android/view/accessibility/AccessibilityManager.java

@@ -459,7 +459,7 @@ public final class AccessibilityManager {
      */
     public boolean addAccessibilityStateChangeListener(
             @NonNull AccessibilityStateChangeListener listener) {
-        // Final CopyOnArrayList - no lock needed.
+        // Final CopyOnWriteArrayList - no lock needed.
         return mAccessibilityStateChangeListeners.add(listener);
     }
 
@@ -471,7 +471,7 @@ public final class AccessibilityManager {
      */
     public boolean removeAccessibilityStateChangeListener(
             @NonNull AccessibilityStateChangeListener listener) {
-        // Final CopyOnArrayList - no lock needed.
+        // Final CopyOnWriteArrayList - no lock needed.
         return mAccessibilityStateChangeListeners.remove(listener);
     }
 
@@ -484,7 +484,7 @@ public final class AccessibilityManager {
      */
     public boolean addTouchExplorationStateChangeListener(
             @NonNull TouchExplorationStateChangeListener listener) {
-        // Final CopyOnArrayList - no lock needed.
+        // Final CopyOnWriteArrayList - no lock needed.
         return mTouchExplorationStateChangeListeners.add(listener);
     }
 
@@ -496,7 +496,7 @@ public final class AccessibilityManager {
      */
     public boolean removeTouchExplorationStateChangeListener(
             @NonNull TouchExplorationStateChangeListener listener) {
-        // Final CopyOnArrayList - no lock needed.
+        // Final CopyOnWriteArrayList - no lock needed.
         return mTouchExplorationStateChangeListeners.remove(listener);
     }
 
@@ -511,7 +511,7 @@ public final class AccessibilityManager {
      */
     public boolean addHighTextContrastStateChangeListener(
             @NonNull HighTextContrastChangeListener listener) {
-        // Final CopyOnArrayList - no lock needed.
+        // Final CopyOnWriteArrayList - no lock needed.
         return mHighTextContrastStateChangeListeners.add(listener);
     }
 
@@ -525,7 +525,7 @@ public final class AccessibilityManager {
      */
     public boolean removeHighTextContrastStateChangeListener(
             @NonNull HighTextContrastChangeListener listener) {
-        // Final CopyOnArrayList - no lock needed.
+        // Final CopyOnWriteArrayList - no lock needed.
         return mHighTextContrastStateChangeListeners.remove(listener);
     }
 
@@ -640,9 +640,9 @@ public final class AccessibilityManager {
         synchronized (mLock) {
             isEnabled = mIsEnabled;
         }
-        final int listenerCount = mAccessibilityStateChangeListeners.size();
-        for (int i = 0; i < listenerCount; i++) {
-            mAccessibilityStateChangeListeners.get(i).onAccessibilityStateChanged(isEnabled);
+        // Listeners are a final CopyOnWriteArrayList, hence no lock needed.
+        for (AccessibilityStateChangeListener listener :mAccessibilityStateChangeListeners) {
+            listener.onAccessibilityStateChanged(isEnabled);
         }
     }
 
@@ -654,10 +654,9 @@ public final class AccessibilityManager {
         synchronized (mLock) {
             isTouchExplorationEnabled = mIsTouchExplorationEnabled;
         }
-        final int listenerCount = mTouchExplorationStateChangeListeners.size();
-        for (int i = 0; i < listenerCount; i++) {
-            mTouchExplorationStateChangeListeners.get(i)
-                    .onTouchExplorationStateChanged(isTouchExplorationEnabled);
+        // Listeners are a final CopyOnWriteArrayList, hence no lock needed.
+        for (TouchExplorationStateChangeListener listener :mTouchExplorationStateChangeListeners) {
+            listener.onTouchExplorationStateChanged(isTouchExplorationEnabled);
         }
     }
 
@@ -669,10 +668,9 @@ public final class AccessibilityManager {
         synchronized (mLock) {
             isHighTextContrastEnabled = mIsHighTextContrastEnabled;
         }
-        final int listenerCount = mHighTextContrastStateChangeListeners.size();
-        for (int i = 0; i < listenerCount; i++) {
-            mHighTextContrastStateChangeListeners.get(i)
-                    .onHighTextContrastStateChanged(isHighTextContrastEnabled);
+        // Listeners are a final CopyOnWriteArrayList, hence no lock needed.
+        for (HighTextContrastChangeListener listener : mHighTextContrastStateChangeListeners) {
+            listener.onHighTextContrastStateChanged(isHighTextContrastEnabled);
         }
     }