diff --git a/core/api/current.txt b/core/api/current.txt
index a3738f767dd5c..ff72863786b24 100644
--- a/core/api/current.txt
+++ b/core/api/current.txt
@@ -39931,7 +39931,7 @@ package android.service.wallpaper {
   public abstract class WallpaperService extends android.app.Service {
     ctor public WallpaperService();
     method public final android.os.IBinder onBind(android.content.Intent);
-    method public abstract android.service.wallpaper.WallpaperService.Engine onCreateEngine();
+    method @MainThread public abstract android.service.wallpaper.WallpaperService.Engine onCreateEngine();
     field public static final String SERVICE_INTERFACE = "android.service.wallpaper.WallpaperService";
     field public static final String SERVICE_META_DATA = "android.service.wallpaper";
   }
@@ -39946,20 +39946,20 @@ package android.service.wallpaper {
     method public boolean isPreview();
     method public boolean isVisible();
     method public void notifyColorsChanged();
-    method public void onApplyWindowInsets(android.view.WindowInsets);
-    method public android.os.Bundle onCommand(String, int, int, int, android.os.Bundle, boolean);
-    method @Nullable public android.app.WallpaperColors onComputeColors();
-    method public void onCreate(android.view.SurfaceHolder);
-    method public void onDesiredSizeChanged(int, int);
-    method public void onDestroy();
-    method public void onOffsetsChanged(float, float, float, float, int, int);
-    method public void onSurfaceChanged(android.view.SurfaceHolder, int, int, int);
-    method public void onSurfaceCreated(android.view.SurfaceHolder);
-    method public void onSurfaceDestroyed(android.view.SurfaceHolder);
-    method public void onSurfaceRedrawNeeded(android.view.SurfaceHolder);
-    method public void onTouchEvent(android.view.MotionEvent);
-    method public void onVisibilityChanged(boolean);
-    method public void onZoomChanged(@FloatRange(from=0.0f, to=1.0f) float);
+    method @MainThread public void onApplyWindowInsets(android.view.WindowInsets);
+    method @MainThread public android.os.Bundle onCommand(String, int, int, int, android.os.Bundle, boolean);
+    method @MainThread @Nullable public android.app.WallpaperColors onComputeColors();
+    method @MainThread public void onCreate(android.view.SurfaceHolder);
+    method @MainThread public void onDesiredSizeChanged(int, int);
+    method @MainThread public void onDestroy();
+    method @MainThread public void onOffsetsChanged(float, float, float, float, int, int);
+    method @MainThread public void onSurfaceChanged(android.view.SurfaceHolder, int, int, int);
+    method @MainThread public void onSurfaceCreated(android.view.SurfaceHolder);
+    method @MainThread public void onSurfaceDestroyed(android.view.SurfaceHolder);
+    method @MainThread public void onSurfaceRedrawNeeded(android.view.SurfaceHolder);
+    method @MainThread public void onTouchEvent(android.view.MotionEvent);
+    method @MainThread public void onVisibilityChanged(boolean);
+    method @MainThread public void onZoomChanged(@FloatRange(from=0.0f, to=1.0f) float);
     method public void setOffsetNotificationsEnabled(boolean);
     method public void setTouchEventsEnabled(boolean);
   }
diff --git a/core/api/system-current.txt b/core/api/system-current.txt
index 4cead54ed0bf8..434ecb1795939 100644
--- a/core/api/system-current.txt
+++ b/core/api/system-current.txt
@@ -12226,7 +12226,7 @@ package android.service.wallpaper {
 
   public class WallpaperService.Engine {
     method public boolean isInAmbientMode();
-    method public void onAmbientModeChanged(boolean, long);
+    method @MainThread public void onAmbientModeChanged(boolean, long);
   }
 
 }
diff --git a/core/java/android/service/wallpaper/WallpaperService.java b/core/java/android/service/wallpaper/WallpaperService.java
index 104570d03b42d..007478a250162 100644
--- a/core/java/android/service/wallpaper/WallpaperService.java
+++ b/core/java/android/service/wallpaper/WallpaperService.java
@@ -31,6 +31,7 @@ import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.animation.ValueAnimator;
 import android.annotation.FloatRange;
+import android.annotation.MainThread;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.SdkConstant;
@@ -657,6 +658,7 @@ public abstract class WallpaperService extends Service {
          * Called once to initialize the engine.  After returning, the
          * engine's surface will be created by the framework.
          */
+        @MainThread
         public void onCreate(SurfaceHolder surfaceHolder) {
         }
 
@@ -665,6 +667,7 @@ public abstract class WallpaperService extends Service {
          * surface will be destroyed and this Engine object is no longer
          * valid.
          */
+        @MainThread
         public void onDestroy() {
         }
 
@@ -673,6 +676,7 @@ public abstract class WallpaperService extends Service {
          * hidden.  <em>It is very important that a wallpaper only use
          * CPU while it is visible.</em>.
          */
+        @MainThread
         public void onVisibilityChanged(boolean visible) {
         }
 
@@ -683,6 +687,7 @@ public abstract class WallpaperService extends Service {
          *
          * @param insets Insets to apply.
          */
+        @MainThread
         public void onApplyWindowInsets(WindowInsets insets) {
         }
 
@@ -693,6 +698,7 @@ public abstract class WallpaperService extends Service {
          * user is interacting with, so if it is slow you will get fewer
          * move events.
          */
+        @MainThread
         public void onTouchEvent(MotionEvent event) {
         }
 
@@ -702,6 +708,7 @@ public abstract class WallpaperService extends Service {
          * call to {@link WallpaperManager#setWallpaperOffsets(IBinder, float, float)
          * WallpaperManager.setWallpaperOffsets()}.
          */
+        @MainThread
         public void onOffsetsChanged(float xOffset, float yOffset,
                 float xOffsetStep, float yOffsetStep,
                 int xPixelOffset, int yPixelOffset) {
@@ -724,6 +731,7 @@ public abstract class WallpaperService extends Service {
          * @return If returning a result, create a Bundle and place the
          * result data in to it.  Otherwise return null.
          */
+        @MainThread
         public Bundle onCommand(String action, int x, int y, int z,
                 Bundle extras, boolean resultRequested) {
             return null;
@@ -742,6 +750,7 @@ public abstract class WallpaperService extends Service {
          * @hide
          */
         @SystemApi
+        @MainThread
         public void onAmbientModeChanged(boolean inAmbientMode, long animationDuration) {
         }
 
@@ -749,6 +758,7 @@ public abstract class WallpaperService extends Service {
          * Called when an application has changed the desired virtual size of
          * the wallpaper.
          */
+        @MainThread
         public void onDesiredSizeChanged(int desiredWidth, int desiredHeight) {
         }
 
@@ -756,6 +766,7 @@ public abstract class WallpaperService extends Service {
          * Convenience for {@link SurfaceHolder.Callback#surfaceChanged
          * SurfaceHolder.Callback.surfaceChanged()}.
          */
+        @MainThread
         public void onSurfaceChanged(SurfaceHolder holder, int format, int width, int height) {
         }
 
@@ -763,6 +774,7 @@ public abstract class WallpaperService extends Service {
          * Convenience for {@link SurfaceHolder.Callback2#surfaceRedrawNeeded
          * SurfaceHolder.Callback.surfaceRedrawNeeded()}.
          */
+        @MainThread
         public void onSurfaceRedrawNeeded(SurfaceHolder holder) {
         }
 
@@ -770,6 +782,7 @@ public abstract class WallpaperService extends Service {
          * Convenience for {@link SurfaceHolder.Callback#surfaceCreated
          * SurfaceHolder.Callback.surfaceCreated()}.
          */
+        @MainThread
         public void onSurfaceCreated(SurfaceHolder holder) {
         }
 
@@ -777,6 +790,7 @@ public abstract class WallpaperService extends Service {
          * Convenience for {@link SurfaceHolder.Callback#surfaceDestroyed
          * SurfaceHolder.Callback.surfaceDestroyed()}.
          */
+        @MainThread
         public void onSurfaceDestroyed(SurfaceHolder holder) {
         }
 
@@ -787,6 +801,7 @@ public abstract class WallpaperService extends Service {
          * @param zoom the zoom level, between 0 indicating fully zoomed in and 1 indicating fully
          *             zoomed out.
          */
+        @MainThread
         public void onZoomChanged(@FloatRange(from = 0f, to = 1f) float zoom) {
         }
 
@@ -836,6 +851,7 @@ public abstract class WallpaperService extends Service {
          *
          * @return Wallpaper colors.
          */
+        @MainThread
         public @Nullable WallpaperColors onComputeColors() {
             return null;
         }
@@ -2510,6 +2526,7 @@ public abstract class WallpaperService extends Service {
      * when the wallpaper is currently set as the active wallpaper and the user
      * is in the wallpaper picker viewing a preview of it as well.
      */
+    @MainThread
     public abstract Engine onCreateEngine();
 
     @Override