Return the existing display ids when registering a display window listener

- This ensures that the caller can synchronously initialize the existing
  displays without waiting for the onDisplayAdded() callback, which can
  happen asynchronously (since the callback is oneway).

Bug: 196186963
Test: atest WMShellUnitTests
Test: atest ActivityTaskManagerServiceTests
Change-Id: I0a8d5f9b4ede7b487a8de14bdb6eaacae7d03d9f

core/java/android/view/IDisplayWindowListener.aidl

@@ -32,7 +32,8 @@ import android.content.res.Configuration;
 oneway interface IDisplayWindowListener {
 
     /**
-     * Called when a display is added to the WM hierarchy.
+     * Called when a new display is added to the WM hierarchy. The existing display ids are returned
+     * when this listener is registered with WM via {@link #registerDisplayWindowListener}.
      */
     void onDisplayAdded(int displayId);
 

core/java/android/view/IWindowManager.aidl

@@ -521,9 +521,10 @@ interface IWindowManager
     void unregisterDisplayFoldListener(IDisplayFoldListener listener);
 
     /**
-     * Registers an IDisplayContainerListener
+     * Registers an IDisplayContainerListener, and returns the set of existing display ids. The
+     * listener's onDisplayAdded() will not be called for the displays returned.
      */
-    void registerDisplayWindowListener(IDisplayWindowListener listener);
+    int[] registerDisplayWindowListener(IDisplayWindowListener listener);
 
     /**
      * Unregisters an IDisplayContainerListener.

libs/WindowManager/Shell/src/com/android/wm/shell/common/DisplayController.java

@@ -67,7 +67,10 @@ public class DisplayController {
      */
     public void initialize() {
         try {
-            mWmService.registerDisplayWindowListener(mDisplayContainerListener);
+            int[] displayIds = mWmService.registerDisplayWindowListener(mDisplayContainerListener);
+            for (int i = 0; i < displayIds.length; i++) {
+                onDisplayAdded(displayIds[i]);
+            }
         } catch (RemoteException e) {
             throw new RuntimeException("Unable to register display controller");
         }

libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/transition/ShellTransitionTests.java

@@ -731,24 +731,12 @@ public class ShellTransitionTests {
         IWindowManager mockWM = mock(IWindowManager.class);
         final IDisplayWindowListener[] displayListener = new IDisplayWindowListener[1];
         try {
-            doAnswer(new Answer() {
-                @Override
-                public Object answer(InvocationOnMock invocation) {
-                    displayListener[0] = invocation.getArgument(0);
-                    return null;
-                }
-            }).when(mockWM).registerDisplayWindowListener(any());
+            doReturn(new int[] {DEFAULT_DISPLAY}).when(mockWM).registerDisplayWindowListener(any());
         } catch (RemoteException e) {
             // No remote stuff happening, so this can't be hit
         }
         DisplayController out = new DisplayController(mContext, mockWM, mMainExecutor);
         out.initialize();
-        try {
-            displayListener[0].onDisplayAdded(DEFAULT_DISPLAY);
-            mMainExecutor.flushAll();
-        } catch (RemoteException e) {
-            // Again, no remote stuff
-        }
         return out;
     }
 

services/core/java/com/android/server/camera/CameraServiceProxy.java

@@ -692,8 +692,11 @@ public class CameraServiceProxy extends SystemService
             }
 
             try {
-                WindowManagerGlobal.getWindowManagerService().registerDisplayWindowListener(
-                        mDisplayWindowListener);
+                int[] displayIds = WindowManagerGlobal.getWindowManagerService()
+                        .registerDisplayWindowListener(mDisplayWindowListener);
+                for (int i = 0; i < displayIds.length; i++) {
+                    mDisplayWindowListener.onDisplayAdded(displayIds[i]);
+                }
             } catch (RemoteException e) {
                 Log.e(TAG, "Failed to register display window listener!");
             }

services/core/java/com/android/server/wm/DisplayWindowListenerController.java

@@ -19,6 +19,7 @@ package com.android.server.wm;
 import android.content.res.Configuration;
 import android.os.RemoteCallbackList;
 import android.os.RemoteException;
+import android.util.IntArray;
 import android.view.IDisplayWindowListener;
 
 /**
@@ -28,23 +29,20 @@ import android.view.IDisplayWindowListener;
 class DisplayWindowListenerController {
     RemoteCallbackList<IDisplayWindowListener> mDisplayListeners = new RemoteCallbackList<>();
 
-//    private final ArrayList<DisplayContainerListener> mDisplayListeners = new ArrayList<>();
     private final WindowManagerService mService;
 
     DisplayWindowListenerController(WindowManagerService service) {
         mService = service;
     }
 
-    void registerListener(IDisplayWindowListener listener) {
+    int[] registerListener(IDisplayWindowListener listener) {
         synchronized (mService.mGlobalLock) {
             mDisplayListeners.register(listener);
-            try {
-                for (int i = 0; i < mService.mAtmService.mRootWindowContainer.getChildCount();
-                        ++i) {
-                    DisplayContent d = mService.mAtmService.mRootWindowContainer.getChildAt(i);
-                    listener.onDisplayAdded(d.mDisplayId);
-                }
-            } catch (RemoteException e) { }
+            final IntArray displayIds = new IntArray();
+            mService.mAtmService.mRootWindowContainer.forAllDisplays((displayContent) -> {
+                displayIds.add(displayContent.mDisplayId);
+            });
+            return displayIds.toArray();
         }
     }
 

services/core/java/com/android/server/wm/WindowManagerService.java

@@ -4340,13 +4340,18 @@ public class WindowManagerService extends IWindowManager.Stub
         }
     }
 
-    /** Registers a hierarchy listener that gets callbacks when the hierarchy changes. */
+    /**
+     * Registers a hierarchy listener that gets callbacks when the hierarchy changes. The listener's
+     * onDisplayAdded() will not be called for the displays returned.
+     *
+     * @return the displayIds for the existing displays
+     */
     @Override
-    public void registerDisplayWindowListener(IDisplayWindowListener listener) {
+    public int[] registerDisplayWindowListener(IDisplayWindowListener listener) {
         mAtmService.enforceTaskPermission("registerDisplayWindowListener");
         final long ident = Binder.clearCallingIdentity();
         try {
-            mDisplayNotificationController.registerListener(listener);
+            return mDisplayNotificationController.registerListener(listener);
         } finally {
             Binder.restoreCallingIdentity(ident);
         }

services/tests/wmtests/src/com/android/server/wm/ActivityTaskManagerServiceTests.java

@@ -173,7 +173,10 @@ public class ActivityTaskManagerServiceTests extends WindowTestsBase {
             @Override
             public void onFixedRotationFinished(int displayId) {}
         };
-        mAtm.mWindowManager.registerDisplayWindowListener(listener);
+        int[] displayIds = mAtm.mWindowManager.registerDisplayWindowListener(listener);
+        for (int i = 0; i < displayIds.length; i++) {
+            added.add(displayIds[i]);
+        }
         // Check that existing displays call added
         assertEquals(mRootWindowContainer.getChildCount(), added.size());
         assertEquals(0, changed.size());