Use an isolated token to represent shell transitions

The Transition object itself used to be the token; however,
this means binder can hold onto it and prevent GC. This is
also more consistent with how WM handles tokens in general

Bug: 258913831
Test: atest TransitionTests
Change-Id: Ibe04cca04dd517629bd2fec707224574293a1bc2

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

@@ -3353,7 +3353,7 @@ class DisplayContent extends RootDisplayArea implements WindowManagerPolicy.Disp
                     }
                 }
                 mWmService.mLatencyTracker.onActionStart(ACTION_ROTATE_SCREEN);
-                controller.mTransitionMetricsReporter.associate(t,
+                controller.mTransitionMetricsReporter.associate(t.getToken(),
                         startTime -> mWmService.mLatencyTracker.onActionEnd(ACTION_ROTATE_SCREEN));
                 startAsyncRotation(false /* shouldDebounce */);
             }

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

@@ -98,6 +98,7 @@ import com.android.server.wm.utils.RotationAnimationUtils;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
@@ -107,7 +108,7 @@ import java.util.function.Predicate;
  * Represents a logical transition.
  * @see TransitionController
  */
-class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListener {
+class Transition implements BLASTSyncEngine.TransactionReadyListener {
     private static final String TAG = "Transition";
     private static final String TRACE_NAME_PLAY_TRANSITION = "PlayTransition";
 
@@ -158,6 +159,7 @@ class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListe
     private @TransitionFlags int mFlags;
     private final TransitionController mController;
     private final BLASTSyncEngine mSyncEngine;
+    private final Token mToken;
     private RemoteTransition mRemoteTransition = null;
 
     /** Only use for clean-up after binder death! */
@@ -220,10 +222,26 @@ class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListe
         mFlags = flags;
         mController = controller;
         mSyncEngine = syncEngine;
+        mToken = new Token(this);
 
         controller.mTransitionTracer.logState(this);
     }
 
+    @Nullable
+    static Transition fromBinder(@NonNull IBinder token) {
+        try {
+            return ((Token) token).mTransition.get();
+        } catch (ClassCastException e) {
+            Slog.w(TAG, "Invalid transition token: " + token, e);
+            return null;
+        }
+    }
+
+    @NonNull
+    IBinder getToken() {
+        return mToken;
+    }
+
     void addFlag(int flag) {
         mFlags |= flag;
     }
@@ -1034,7 +1052,7 @@ class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListe
                 ProtoLog.v(ProtoLogGroup.WM_DEBUG_WINDOW_TRANSITIONS,
                         "Calling onTransitionReady: %s", info);
                 mController.getTransitionPlayer().onTransitionReady(
-                        this, info, transaction, mFinishTransaction);
+                        mToken, info, transaction, mFinishTransaction);
                 if (Trace.isTagEnabled(TRACE_TAG_WINDOW_MANAGER)) {
                     Trace.asyncTraceBegin(TRACE_TAG_WINDOW_MANAGER, TRACE_NAME_PLAY_TRANSITION,
                             System.identityHashCode(this));
@@ -1067,7 +1085,7 @@ class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListe
         if (mFinishTransaction != null) {
             mFinishTransaction.apply();
         }
-        mController.finishTransition(this);
+        mController.finishTransition(mToken);
     }
 
     /** @see RecentsAnimationController#attachNavigationBarToApp */
@@ -1850,10 +1868,6 @@ class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListe
         return isCollecting() && mSyncId >= 0;
     }
 
-    static Transition fromBinder(IBinder binder) {
-        return (Transition) binder;
-    }
-
     @VisibleForTesting
     static class ChangeInfo {
         private static final int FLAG_NONE = 0;
@@ -2345,4 +2359,18 @@ class Transition extends Binder implements BLASTSyncEngine.TransactionReadyListe
             }
         }
     }
+
+    private static class Token extends Binder {
+        final WeakReference<Transition> mTransition;
+
+        Token(Transition transition) {
+            mTransition = new WeakReference<>(transition);
+        }
+
+        @Override
+        public String toString() {
+            return "Token{" + Integer.toHexString(System.identityHashCode(this)) + " "
+                    + mTransition.get() + "}";
+        }
+    }
 }

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

@@ -458,8 +458,9 @@ class TransitionController {
                 info = new ActivityManager.RunningTaskInfo();
                 startTask.fillTaskInfo(info);
             }
-            mTransitionPlayer.requestStartTransition(transition, new TransitionRequestInfo(
-                    transition.mType, info, remoteTransition, displayChange));
+            mTransitionPlayer.requestStartTransition(transition.getToken(),
+                    new TransitionRequestInfo(transition.mType, info, remoteTransition,
+                            displayChange));
             transition.setRemoteTransition(remoteTransition);
         } catch (RemoteException e) {
             Slog.e(TAG, "Error requesting transition", e);

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

@@ -307,7 +307,7 @@ class WindowOrganizerController extends IWindowOrganizerController.Stub
                                         nextTransition.setAllReady();
                                     }
                                 });
-                        return nextTransition;
+                        return nextTransition.getToken();
                     }
                     transition = mTransitionController.createTransition(type);
                 }
@@ -316,7 +316,7 @@ class WindowOrganizerController extends IWindowOrganizerController.Stub
                 if (needsSetReady) {
                     transition.setAllReady();
                 }
-                return transition;
+                return transition.getToken();
             }
         } finally {
             Binder.restoreCallingIdentity(ident);

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

@@ -369,7 +369,7 @@ public class WallpaperControllerTests extends WindowTestsBase {
         final SurfaceControl.Transaction t = mock(SurfaceControl.Transaction.class);
         token.finishSync(t, false /* cancel */);
         transit.onTransactionReady(transit.getSyncId(), t);
-        dc.mTransitionController.finishTransition(transit);
+        dc.mTransitionController.finishTransition(transit.getToken());
         assertFalse(wallpaperWindow.isVisible());
         assertFalse(token.isVisible());
 

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

@@ -1731,7 +1731,7 @@ class WindowTestsBase extends SystemServiceTestsBase {
         }
 
         void startTransition() {
-            mOrganizer.startTransition(mLastTransit, null);
+            mOrganizer.startTransition(mLastTransit.getToken(), null);
         }
 
         void onTransactionReady(SurfaceControl.Transaction t) {
@@ -1744,7 +1744,7 @@ class WindowTestsBase extends SystemServiceTestsBase {
         }
 
         public void finish() {
-            mController.finishTransition(mLastTransit);
+            mController.finishTransition(mLastTransit.getToken());
         }
     }
 }