Fix java.lang.ArrayIndexOutOfBoundsException at ArraySet in GenericWindowPolicyController.onRunningAppsChanged()

- Before iterating over mRunningAppsChangedListener, we need to confirm
  whether there is a listener in mRunningAppsChangedListener to avoid
  ArrayIndexOutOfBoundsException.
- Use mGenericWindowPolicyControllerLock to protect
  mRunningAppsChangedListener access.

Bug: 248192490
Test: Manual
Change-Id: Iedd031f50659f027576086788392110a3432858a

services/companion/java/com/android/server/companion/virtual/GenericWindowPolicyController.java

@@ -44,6 +44,7 @@ import android.view.Display;
 import android.window.DisplayWindowPolicyController;
 
 import com.android.internal.annotations.GuardedBy;
+import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.app.BlockedAppStreamingActivity;
 
 import java.util.List;
@@ -112,7 +113,9 @@ public class GenericWindowPolicyController extends DisplayWindowPolicyController
     final ArraySet<Integer> mRunningUids = new ArraySet<>();
     @Nullable private final ActivityListener mActivityListener;
     private final Handler mHandler = new Handler(Looper.getMainLooper());
-    private final ArraySet<RunningAppsChangedListener> mRunningAppsChangedListener =
+    @NonNull
+    @GuardedBy("mGenericWindowPolicyControllerLock")
+    private final ArraySet<RunningAppsChangedListener> mRunningAppsChangedListeners =
             new ArraySet<>();
     @Nullable
     private final @AssociationRequest.DeviceProfile String mDeviceProfile;
@@ -178,12 +181,16 @@ public class GenericWindowPolicyController extends DisplayWindowPolicyController
 
     /** Register a listener for running applications changes. */
     public void registerRunningAppsChangedListener(@NonNull RunningAppsChangedListener listener) {
-        mRunningAppsChangedListener.add(listener);
+        synchronized (mGenericWindowPolicyControllerLock) {
+            mRunningAppsChangedListeners.add(listener);
+        }
     }
 
     /** Unregister a listener for running applications changes. */
     public void unregisterRunningAppsChangedListener(@NonNull RunningAppsChangedListener listener) {
-        mRunningAppsChangedListener.remove(listener);
+        synchronized (mGenericWindowPolicyControllerLock) {
+            mRunningAppsChangedListeners.remove(listener);
+        }
     }
 
     @Override
@@ -283,12 +290,16 @@ public class GenericWindowPolicyController extends DisplayWindowPolicyController
                 // Post callback on the main thread so it doesn't block activity launching
                 mHandler.post(() -> mActivityListener.onDisplayEmpty(mDisplayId));
             }
-        }
-        mHandler.post(() -> {
-            for (RunningAppsChangedListener listener : mRunningAppsChangedListener) {
-                listener.onRunningAppsChanged(runningUids);
+            if (!mRunningAppsChangedListeners.isEmpty()) {
+                final ArraySet<RunningAppsChangedListener> listeners =
+                        new ArraySet<>(mRunningAppsChangedListeners);
+                mHandler.post(() -> {
+                    for (RunningAppsChangedListener listener : listeners) {
+                        listener.onRunningAppsChanged(runningUids);
+                    }
+                });
             }
-        });
+        }
     }
 
     @Override
@@ -354,4 +365,11 @@ public class GenericWindowPolicyController extends DisplayWindowPolicyController
         }
         return true;
     }
+
+    @VisibleForTesting
+    int getRunningAppsChangedListenersSizeForTesting() {
+        synchronized (mGenericWindowPolicyControllerLock) {
+            return mRunningAppsChangedListeners.size();
+        }
+    }
 }

services/tests/servicestests/src/com/android/server/companion/virtual/VirtualDeviceManagerServiceTest.java

@@ -891,4 +891,34 @@ public class VirtualDeviceManagerServiceTest {
         verify(mContext).startActivityAsUser(argThat(intent ->
                 intent.filterEquals(blockedAppIntent)), any(), any());
     }
+
+    @Test
+    public void registerRunningAppsChangedListener_onRunningAppsChanged_listenersNotified() {
+        ArraySet<Integer> uids = new ArraySet<>(Arrays.asList(UID_1, UID_2));
+        mDeviceImpl.onVirtualDisplayCreatedLocked(
+                mDeviceImpl.createWindowPolicyController(), DISPLAY_ID);
+        GenericWindowPolicyController gwpc = mDeviceImpl.getWindowPolicyControllersForTesting().get(
+                DISPLAY_ID);
+
+        gwpc.onRunningAppsChanged(uids);
+        mDeviceImpl.onRunningAppsChanged(uids);
+
+        assertThat(gwpc.getRunningAppsChangedListenersSizeForTesting()).isEqualTo(1);
+        verify(mRunningAppsChangedCallback).accept(new ArraySet<>(Arrays.asList(UID_1, UID_2)));
+    }
+
+    @Test
+    public void noRunningAppsChangedListener_onRunningAppsChanged_doesNotThrowException() {
+        ArraySet<Integer> uids = new ArraySet<>(Arrays.asList(UID_1, UID_2));
+        mDeviceImpl.onVirtualDisplayCreatedLocked(
+                mDeviceImpl.createWindowPolicyController(), DISPLAY_ID);
+        GenericWindowPolicyController gwpc = mDeviceImpl.getWindowPolicyControllersForTesting().get(
+                DISPLAY_ID);
+        mDeviceImpl.onVirtualDisplayRemovedLocked(DISPLAY_ID);
+
+        // This call should not throw any exceptions.
+        gwpc.onRunningAppsChanged(uids);
+
+        assertThat(gwpc.getRunningAppsChangedListenersSizeForTesting()).isEqualTo(0);
+    }
 }