Check if already on main thread when getting SSG for SCVH

SCVH can be added in process so if they are included in a SSG
the call to getSurfaceSyncGroup could run on the main thread.
If this were the case, the method would never return a value
since the call is is blocking and waiting to run on the main
thread. Instead, check if the incoming thread is the main thread
and return a value immediately instead of a post to main thread.

Change-Id: Id233eecc46afb1f5425df97986e7563e970aff12
Bug: 276356641
Test: SurfaceSyncGroupContinuousTest

core/java/android/view/SurfaceControlViewHost.java

@@ -99,9 +99,16 @@ public class SurfaceControlViewHost {
         @Override
         public ISurfaceSyncGroup getSurfaceSyncGroup() {
             CompletableFuture<ISurfaceSyncGroup> surfaceSyncGroup = new CompletableFuture<>();
-            mViewRoot.mHandler.post(
-                    () -> surfaceSyncGroup.complete(
-                            mViewRoot.getOrCreateSurfaceSyncGroup().mISurfaceSyncGroup));
+            // If the call came from in process and it's already running on the UI thread, return
+            // results immediately instead of posting to the main thread. If we post to the main
+            // thread, it will block itself and the return value will always be null.
+            if (Thread.currentThread() == mViewRoot.mThread) {
+                return mViewRoot.getOrCreateSurfaceSyncGroup().mISurfaceSyncGroup;
+            } else {
+                mViewRoot.mHandler.post(
+                        () -> surfaceSyncGroup.complete(
+                                mViewRoot.getOrCreateSurfaceSyncGroup().mISurfaceSyncGroup));
+            }
             try {
                 return surfaceSyncGroup.get(1, TimeUnit.SECONDS);
             } catch (InterruptedException | ExecutionException | TimeoutException e) {