Raise Handler ThreadPrority for IMMS

IMMS used the main thread with default priority
to create own Handler to deal with picker showing,
surface removal, and update input method list, etc.

Improve it by creating a dedicated thread with the
"THREAD_PRIORITY_FOREGROUND" priority to decouple
IMMS#mHandler from other task executions on the main
thread of system_server and reduce the likelihood of
priority inversion in IMMS.

Bug: 190486491
Bug: 167948374
Test: atest CtsInputMethodTestCases
Change-Id: Ia85df9c3e8b26f6fcbeaf269d47e929f178c9285

1 files changed, 13 insertions, 6 deletions

diff --git a/services/core/java/com/android/server/inputmethod/InputMethodManagerService.java b/services/core/java/com/android/server/inputmethod/InputMethodManagerService.java
index 35c0e9abf7ba..02bc1e963321 100644
--- a/services/core/java/com/android/server/inputmethod/InputMethodManagerService.java
+++ b/services/core/java/com/android/server/inputmethod/InputMethodManagerService.java
@@ -58,10 +58,10 @@ import android.annotation.BinderThread;
 import android.annotation.ColorInt;
 import android.annotation.DrawableRes;
 import android.annotation.IntDef;
-import android.annotation.MainThread;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.RequiresPermission;
+import android.annotation.UiThread;
 import android.annotation.UserIdInt;
 import android.app.ActivityManager;
 import android.app.ActivityManagerInternal;
@@ -182,6 +182,7 @@ import com.android.internal.view.IInputSessionCallback;
 import com.android.internal.view.InlineSuggestionsRequestInfo;
 import com.android.server.EventLogTags;
 import com.android.server.LocalServices;
+import com.android.server.ServiceThread;
 import com.android.server.SystemService;
 import com.android.server.inputmethod.InputMethodManagerInternal.InputMethodListListener;
 import com.android.server.inputmethod.InputMethodSubtypeSwitchingController.ImeSubtypeListItem;
@@ -262,6 +263,7 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
 
     private static final int NOT_A_SUBTYPE_ID = InputMethodUtils.NOT_A_SUBTYPE_ID;
     private static final String TAG_TRY_SUPPRESSING_IME_SWITCHER = "TrySuppressingImeSwitcher";
+    private static final String HANDLER_THREAD_NAME = "android.imms";
 
     /**
      * Binding flags for establishing connection to the {@link InputMethodService}.
@@ -1592,7 +1594,12 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
         mIPackageManager = AppGlobals.getPackageManager();
         mContext = context;
         mRes = context.getResources();
-        mHandler = new Handler(this);
+        // TODO(b/196206770): Disallow I/O on this thread. Currently it's needed for loading
+        // additional subtypes in switchUserOnHandlerLocked().
+        final ServiceThread thread = new ServiceThread(
+                HANDLER_THREAD_NAME, Process.THREAD_PRIORITY_FOREGROUND, true /* allowIo */);
+        thread.start();
+        mHandler = Handler.createAsync(thread.getLooper(), this);
         // Note: SettingsObserver doesn't register observers in its constructor.
         mSettingsObserver = new SettingsObserver(mHandler);
         mIWindowManager = IWindowManager.Stub.asInterface(
@@ -1601,7 +1608,7 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
         mPackageManagerInternal = LocalServices.getService(PackageManagerInternal.class);
         mInputManagerInternal = LocalServices.getService(InputManagerInternal.class);
         mImeDisplayValidator = displayId -> mWindowManagerInternal.getDisplayImePolicy(displayId);
-        mCaller = new HandlerCaller(context, null, new HandlerCaller.Callback() {
+        mCaller = new HandlerCaller(context, thread.getLooper(), new HandlerCaller.Callback() {
             @Override
             public void executeMessage(Message msg) {
                 handleMessage(msg);
@@ -4159,7 +4166,7 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
         Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
     }
 
-    void setEnabledSessionInMainThread(SessionState session) {
+    void setEnabledSessionInHandlerThread(SessionState session) {
         if (mEnabledSession != session) {
             if (mEnabledSession != null && mEnabledSession.session != null) {
                 try {
@@ -4179,7 +4186,7 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
         }
     }
 
-    @MainThread
+    @UiThread
     @Override
     public boolean handleMessage(Message msg) {
         SomeArgs args;
@@ -4356,7 +4363,7 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
                 final IInputContext inputContext = (IInputContext) args.arg3;
                 final EditorInfo editorInfo = (EditorInfo) args.arg4;
                 try {
-                    setEnabledSessionInMainThread(session);
+                    setEnabledSessionInHandlerThread(session);
                     session.method.startInput(startInputToken, inputContext, missingMethods,
                             editorInfo, restarting);
                 } catch (RemoteException e) {