diff --git a/services/core/java/com/android/server/am/UserController.java b/services/core/java/com/android/server/am/UserController.java
index a7472d8..3abfe082 100644
--- a/services/core/java/com/android/server/am/UserController.java
+++ b/services/core/java/com/android/server/am/UserController.java
@@ -154,6 +154,9 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Objects;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
 
@@ -220,18 +223,9 @@
     private static final int USER_SWITCH_CALLBACKS_TIMEOUT_MS = 5 * 1000;
 
     /**
-     * Amount of time waited for
-     * {@link ActivityTaskManagerInternal.ScreenObserver#onKeyguardStateChanged} callbacks to be
-     * called after calling {@link WindowManagerService#lockDeviceNow}.
-     * Otherwise, we should throw a {@link RuntimeException} and never dismiss the
-     * {@link UserSwitchingDialog}.
-     */
-    static final int SHOW_KEYGUARD_TIMEOUT_MS = 20 * 1000;
-
-    /**
      * Amount of time waited for {@link WindowManagerService#dismissKeyguard} callbacks to be
      * called after dismissing the keyguard.
-     * Otherwise, we should move on to dismiss the dialog {@link #dismissUserSwitchDialog}}
+     * Otherwise, we should move on to dismiss the dialog {@link #dismissUserSwitchDialog()}
      * and report user switch is complete {@link #REPORT_USER_SWITCH_COMPLETE_MSG}.
      */
     private static final int DISMISS_KEYGUARD_TIMEOUT_MS = 2 * 1000;
@@ -1828,8 +1822,15 @@
                 updateProfileRelatedCaches();
                 mInjector.getWindowManager().setCurrentUser(userId);
                 mInjector.reportCurWakefulnessUsageEvent();
+                // Once the internal notion of the active user has switched, we lock the device
+                // with the option to show the user switcher on the keyguard.
                 if (userSwitchUiEnabled) {
                     mInjector.getWindowManager().setSwitchingUser(true);
+                    // Only lock if the user has a secure keyguard PIN/Pattern/Pwd
+                    if (mInjector.getKeyguardManager().isDeviceSecure(userId)) {
+                        // Make sure the device is locked before moving on with the user switch
+                        mInjector.lockDeviceNowAndWaitForKeyguardShown();
+                    }
                 }
 
             } else {
@@ -2340,56 +2341,34 @@
 
     @VisibleForTesting
     void completeUserSwitch(int oldUserId, int newUserId) {
-        final Runnable sendUserSwitchCompleteMessage = () -> {
-            mHandler.removeMessages(REPORT_USER_SWITCH_COMPLETE_MSG);
-            mHandler.sendMessage(mHandler.obtainMessage(
-                    REPORT_USER_SWITCH_COMPLETE_MSG, oldUserId, newUserId));
-        };
-        if (isUserSwitchUiEnabled()) {
-            if (mInjector.getKeyguardManager().isDeviceSecure(newUserId)) {
-                this.showKeyguard(() -> dismissUserSwitchDialog(sendUserSwitchCompleteMessage));
-            } else {
-                this.dismissKeyguard(() -> dismissUserSwitchDialog(sendUserSwitchCompleteMessage));
-            }
+        final boolean isUserSwitchUiEnabled = isUserSwitchUiEnabled();
+        // serialize each conditional step
+        await(
+                // STEP 1 - If there is no challenge set, dismiss the keyguard right away
+                isUserSwitchUiEnabled && !mInjector.getKeyguardManager().isDeviceSecure(newUserId),
+                mInjector::dismissKeyguard,
+                () -> await(
+                        // STEP 2 - If user switch ui was enabled, dismiss user switch dialog
+                        isUserSwitchUiEnabled,
+                        this::dismissUserSwitchDialog,
+                        () -> {
+                            // STEP 3 - Send REPORT_USER_SWITCH_COMPLETE_MSG to broadcast
+                            // ACTION_USER_SWITCHED & call UserSwitchObservers.onUserSwitchComplete
+                            mHandler.removeMessages(REPORT_USER_SWITCH_COMPLETE_MSG);
+                            mHandler.sendMessage(mHandler.obtainMessage(
+                                    REPORT_USER_SWITCH_COMPLETE_MSG, oldUserId, newUserId));
+                        }
+                ));
+    }
+
+    private void await(boolean condition, Consumer<Runnable> conditionalStep, Runnable nextStep) {
+        if (condition) {
+            conditionalStep.accept(nextStep);
         } else {
-            sendUserSwitchCompleteMessage.run();
+            nextStep.run();
         }
     }
 
-    protected void showKeyguard(Runnable runnable) {
-        runWithTimeout(mInjector::showKeyguard, SHOW_KEYGUARD_TIMEOUT_MS, runnable, () -> {
-            throw new RuntimeException(
-                    "Keyguard is not shown in " + SHOW_KEYGUARD_TIMEOUT_MS + " ms.");
-        }, "showKeyguard");
-    }
-
-    protected void dismissKeyguard(Runnable runnable) {
-        runWithTimeout(mInjector::dismissKeyguard, DISMISS_KEYGUARD_TIMEOUT_MS, runnable, runnable,
-                "dismissKeyguard");
-    }
-
-    private void runWithTimeout(Consumer<Runnable> task, int timeoutMs, Runnable onSuccess,
-            Runnable onTimeout, String traceMsg) {
-        final AtomicInteger state = new AtomicInteger(0); // state = 0 (RUNNING)
-
-        asyncTraceBegin(traceMsg, 0);
-
-        mHandler.postDelayed(() -> {
-            if (state.compareAndSet(0, 1)) { // state = 1 (TIMEOUT)
-                asyncTraceEnd(traceMsg, 0);
-                Slogf.w(TAG, "Timeout: %s did not finish in %d ms", traceMsg, timeoutMs);
-                onTimeout.run();
-            }
-        }, timeoutMs);
-
-        task.accept(() -> {
-            if (state.compareAndSet(0, 2)) { // state = 2 (SUCCESS)
-                asyncTraceEnd(traceMsg, 0);
-                onSuccess.run();
-            }
-        });
-    }
-
     private void moveUserToForeground(UserState uss, int newUserId) {
         boolean homeInFront = mInjector.taskSupervisorSwitchUser(newUserId, uss);
         if (homeInFront) {
@@ -3826,45 +3805,29 @@
             return IStorageManager.Stub.asInterface(ServiceManager.getService("mount"));
         }
 
-        protected void showKeyguard(Runnable runnable) {
-            if (getWindowManager().isKeyguardLocked()) {
-                runnable.run();
-                return;
-            }
-            getActivityTaskManagerInternal().registerScreenObserver(
-                    new ActivityTaskManagerInternal.ScreenObserver() {
-                        @Override
-                        public void onAwakeStateChanged(boolean isAwake) {
-
-                        }
-
-                        @Override
-                        public void onKeyguardStateChanged(boolean isShowing) {
-                            if (isShowing) {
-                                getActivityTaskManagerInternal().unregisterScreenObserver(this);
-                                runnable.run();
-                            }
-                        }
-                    }
-            );
-            getWindowManager().lockDeviceNow();
-        }
-
         protected void dismissKeyguard(Runnable runnable) {
+            final AtomicBoolean isFirst = new AtomicBoolean(true);
+            final Runnable runOnce = () -> {
+                if (isFirst.getAndSet(false)) {
+                    runnable.run();
+                }
+            };
+
+            mHandler.postDelayed(runOnce, DISMISS_KEYGUARD_TIMEOUT_MS);
             getWindowManager().dismissKeyguard(new IKeyguardDismissCallback.Stub() {
                 @Override
                 public void onDismissError() throws RemoteException {
-                    runnable.run();
+                    mHandler.post(runOnce);
                 }
 
                 @Override
                 public void onDismissSucceeded() throws RemoteException {
-                    runnable.run();
+                    mHandler.post(runOnce);
                 }
 
                 @Override
                 public void onDismissCancelled() throws RemoteException {
-                    runnable.run();
+                    mHandler.post(runOnce);
                 }
             }, /* message= */ null);
         }
@@ -3890,5 +3853,43 @@
         void onSystemUserVisibilityChanged(boolean visible) {
             getUserManagerInternal().onSystemUserVisibilityChanged(visible);
         }
+
+        void lockDeviceNowAndWaitForKeyguardShown() {
+            if (getWindowManager().isKeyguardLocked()) {
+                return;
+            }
+
+            final TimingsTraceAndSlog t = new TimingsTraceAndSlog();
+            t.traceBegin("lockDeviceNowAndWaitForKeyguardShown");
+
+            final CountDownLatch latch = new CountDownLatch(1);
+            ActivityTaskManagerInternal.ScreenObserver screenObserver =
+                    new ActivityTaskManagerInternal.ScreenObserver() {
+                        @Override
+                        public void onAwakeStateChanged(boolean isAwake) {
+
+                        }
+
+                        @Override
+                        public void onKeyguardStateChanged(boolean isShowing) {
+                            if (isShowing) {
+                                latch.countDown();
+                            }
+                        }
+                    };
+
+            getActivityTaskManagerInternal().registerScreenObserver(screenObserver);
+            getWindowManager().lockDeviceNow();
+            try {
+                if (!latch.await(20, TimeUnit.SECONDS)) {
+                    throw new RuntimeException("Keyguard is not shown in 20 seconds");
+                }
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            } finally {
+                getActivityTaskManagerInternal().unregisterScreenObserver(screenObserver);
+                t.traceEnd();
+            }
+        }
     }
 }
diff --git a/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java b/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java
index 851c451..cea10ea 100644
--- a/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java
+++ b/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java
@@ -57,7 +57,6 @@
 import static org.mockito.Matchers.anyBoolean;
 import static org.mockito.Matchers.anyInt;
 import static org.mockito.Matchers.eq;
-import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.doCallRealMethod;
 import static org.mockito.Mockito.doNothing;
@@ -90,7 +89,6 @@
 import android.os.Message;
 import android.os.PowerManagerInternal;
 import android.os.RemoteException;
-import android.os.SystemClock;
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.os.storage.IStorageManager;
@@ -200,10 +198,7 @@
             doNothing().when(mInjector).activityManagerOnUserStopped(anyInt());
             doNothing().when(mInjector).clearBroadcastQueueForUser(anyInt());
             doNothing().when(mInjector).taskSupervisorRemoveUser(anyInt());
-            doAnswer(invocation -> {
-                ((Runnable) invocation.getArgument(0)).run();
-                return null;
-            }).when(mInjector).showKeyguard(any());
+            doNothing().when(mInjector).lockDeviceNowAndWaitForKeyguardShown();
             mockIsUsersOnSecondaryDisplaysEnabled(false);
             // All UserController params are set to default.
 
@@ -535,6 +530,7 @@
         expectedCodes.add(REPORT_USER_SWITCH_COMPLETE_MSG);
         if (backgroundUserStopping) {
             expectedCodes.add(CLEAR_USER_JOURNEY_SESSION_MSG);
+            expectedCodes.add(0); // this is for directly posting in stopping.
         }
         Set<Integer> actualCodes = mInjector.mHandler.getMessageCodes();
         assertEquals("Unexpected message sent", expectedCodes, actualCodes);
@@ -1051,13 +1047,21 @@
         // mock the device to be secure in order to expect the keyguard to be shown
         when(mInjector.mKeyguardManagerMock.isDeviceSecure(anyInt())).thenReturn(true);
 
-        // call real showKeyguard method for this test
-        doCallRealMethod().when(mInjector).showKeyguard(any());
+        // call real lockDeviceNowAndWaitForKeyguardShown method for this test
+        doCallRealMethod().when(mInjector).lockDeviceNowAndWaitForKeyguardShown();
 
-        mUserController.completeUserSwitch(TEST_USER_ID1, TEST_USER_ID2);
+        // call startUser on a thread because we're expecting it to be blocked
+        Thread threadStartUser = new Thread(()-> {
+            mUserController.startUser(TEST_USER_ID, USER_START_MODE_FOREGROUND);
+        });
+        threadStartUser.start();
 
-        // make sure the switch is stalled by checking the UserSwitchingDialog is not dismissed yet
-        verify(mInjector, never()).dismissUserSwitchingDialog(any());
+        // make sure the switch is stalled...
+        Thread.sleep(2000);
+        // by checking REPORT_USER_SWITCH_MSG is not sent yet
+        assertNull(mInjector.mHandler.getMessageForCode(REPORT_USER_SWITCH_MSG));
+        // and the thread is still alive
+        assertTrue(threadStartUser.isAlive());
 
         // mock send the keyguard shown event
         ArgumentCaptor<ActivityTaskManagerInternal.ScreenObserver> captor = ArgumentCaptor.forClass(
@@ -1065,41 +1069,12 @@
         verify(mInjector.mActivityTaskManagerInternal).registerScreenObserver(captor.capture());
         captor.getValue().onKeyguardStateChanged(true);
 
-        // verify the switch now moves on by checking the UserSwitchingDialog is dismissed
-        verify(mInjector, atLeastOnce()).dismissUserSwitchingDialog(any());
-
-        // verify that SHOW_KEYGUARD_TIMEOUT is ignored and does not crash the system
-        try {
-            mInjector.mHandler.processPostDelayedCallbacksWithin(
-                    UserController.SHOW_KEYGUARD_TIMEOUT_MS);
-        } catch (RuntimeException e) {
-            throw new AssertionError(
-                    "SHOW_KEYGUARD_TIMEOUT is not ignored and crashed the system", e);
-        }
-    }
-
-    @Test
-    public void testRuntimeExceptionIsThrownIfTheKeyguardIsNotShown() throws Exception {
-        // enable user switch ui, because keyguard is only shown then
-        mUserController.setInitialConfig(/* userSwitchUiEnabled= */ true,
-                /* maxRunningUsers= */ 3, /* delayUserDataLocking= */ false);
-
-        // mock the device to be secure in order to expect the keyguard to be shown
-        when(mInjector.mKeyguardManagerMock.isDeviceSecure(anyInt())).thenReturn(true);
-
-        // suppress showKeyguard method for this test
-        doNothing().when(mInjector).showKeyguard(any());
-
-        mUserController.completeUserSwitch(TEST_USER_ID1, TEST_USER_ID2);
-
-        // verify that the system has crashed
-        assertThrows("Should have thrown RuntimeException", RuntimeException.class, () -> {
-            mInjector.mHandler.processPostDelayedCallbacksWithin(
-                    UserController.SHOW_KEYGUARD_TIMEOUT_MS);
-        });
-
-        // make sure the UserSwitchingDialog is not dismissed
-        verify(mInjector, never()).dismissUserSwitchingDialog(any());
+        // verify the switch now moves on...
+        Thread.sleep(1000);
+        // by checking REPORT_USER_SWITCH_MSG is sent
+        assertNotNull(mInjector.mHandler.getMessageForCode(REPORT_USER_SWITCH_MSG));
+        // and the thread is finished
+        assertFalse(threadStartUser.isAlive());
     }
 
     private void setUpAndStartUserInBackground(int userId) throws Exception {
@@ -1435,9 +1410,7 @@
         Set<Integer> getMessageCodes() {
             Set<Integer> result = new LinkedHashSet<>();
             for (Message msg : mMessages) {
-                if (msg.what != 0) { // ignore mHandle.post and mHandler.postDelayed messages
-                    result.add(msg.what);
-                }
+                result.add(msg.what);
             }
             return result;
         }
@@ -1461,28 +1434,14 @@
 
         @Override
         public boolean sendMessageAtTime(Message msg, long uptimeMillis) {
-            final Runnable cb = msg.getCallback();
-            if (cb != null && uptimeMillis <= SystemClock.uptimeMillis()) {
-                // run mHandler.post calls immediately
-                cb.run();
-                return true;
-            }
             Message copy = new Message();
             copy.copyFrom(msg);
-            copy.setCallback(cb);
             mMessages.add(copy);
-            return super.sendMessageAtTime(msg, uptimeMillis);
-        }
-
-        public void processPostDelayedCallbacksWithin(long millis) {
-            final long whenMax = SystemClock.uptimeMillis() + millis;
-            for (Message msg : mMessages) {
-                final Runnable cb = msg.getCallback();
-                if (cb != null && msg.getWhen() <= whenMax) {
-                    msg.setCallback(null);
-                    cb.run();
-                }
+            if (msg.getCallback() != null) {
+                msg.getCallback().run();
+                msg.setCallback(null);
             }
+            return super.sendMessageAtTime(msg, uptimeMillis);
         }
     }
 }