Simplify handler initialization for InputConnectionFactory

content/public/android/java/src/org/chromium/content/browser/input/ThreadedInputConnectionFactory.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.content.browser.input;
 
 import android.os.Handler;
 import android.os.HandlerThread;
 import android.view.View;
 import android.view.inputmethod.EditorInfo;
 
 import org.chromium.base.Log;
 import org.chromium.base.VisibleForTesting;
-import org.chromium.base.annotations.SuppressFBWarnings;
 
 /**
  * A factory class for {@link ThreadedInputConnection}. The class also includes triggering
  * mechanism (hack) to run our InputConnection on non-UI thread.
  */
 // TODO(changwan): add unit tests once Robolectric supports Android API level >= 21.
 // See crbug.com/588547 for details.
 public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnection.Factory {
     private static final String TAG = "cr_Ime";
     private static final boolean DEBUG_LOGS = false;
 
     // Most of the time we do not need to retry. But if we have lost window focus while triggering
     // delayed creation, then there is a chance that detection may fail in the following scenario:
     // InputMethodManagerService checks the window focus by directly calling
     // WindowManagerService#inputMethodClientHasFocus(). But the window focus change is
     // propagated to the view via ViewRootImpl's message queue. Therefore, it may take another
     // UI message loop until View#hasWindowFocus() is aligned with what IMMS sees.
     private static final int CHECK_REGISTER_RETRY = 1;
 
-    // Reused for multiple WebView instances. TODO(changwan): check if we need to quit the loop
-    // for the last webview instance.
-    private static HandlerThread sHandlerThread;
-
-    private final Handler mHandler;
     private final InputMethodManagerWrapper mInputMethodManagerWrapper;
     private final InputMethodUma mInputMethodUma;
     private ThreadedInputConnectionProxyView mProxyView;
     private ThreadedInputConnection mThreadedInputConnection;
     private CheckInvalidator mCheckInvalidator;
     private boolean mReentrantTriggering;
 
+    // Initialization-on-demand holder for Handler.
+    private static class LazyHandlerHolder {
+        // Note that we never exit this thread to avoid lifetime or thread-safety issues.
+        private static final Handler sHandler;
+        static {
+            HandlerThread handlerThread =
+                    new HandlerThread("InputConnectionHandlerThread", HandlerThread.NORM_PRIORITY);
+            handlerThread.start();
+            sHandler = new Handler(handlerThread.getLooper());
+        }
+    }
+
     // A small class that can be updated to invalidate the check when there is an external event
     // such as window focus loss or view focus loss.
     private static class CheckInvalidator {
         private boolean mInvalid;
 
         public void invalidate() {
             ImeUtils.checkOnUiThread();
             mInvalid = true;
         }
 
         public boolean isInvalid() {
             ImeUtils.checkOnUiThread();
             return mInvalid;
         }
     }
 
     ThreadedInputConnectionFactory(InputMethodManagerWrapper inputMethodManagerWrapper) {
         mInputMethodManagerWrapper = inputMethodManagerWrapper;
-        mHandler = createHandler();
         mInputMethodUma = createInputMethodUma();
     }
 
-    @VisibleForTesting
-    @SuppressFBWarnings("LI_LAZY_INIT_UPDATE_STATIC")
-    protected Handler createHandler() {
-        if (sHandlerThread == null) {
-            sHandlerThread =
-                    new HandlerThread("InputConnectionHandlerThread", HandlerThread.NORM_PRIORITY);
-            sHandlerThread.start();
-        }
-        return new Handler(sHandlerThread.getLooper());
+    @Override
+    public Handler getHandler() {
+        return LazyHandlerHolder.sHandler;
     }
 
     @VisibleForTesting
     protected ThreadedInputConnectionProxyView createProxyView(
             Handler handler, View containerView) {
         return new ThreadedInputConnectionProxyView(
                 containerView.getContext(), handler, containerView);
     }
 
     @VisibleForTesting
@@ skipping 39 matching lines @@
         if (mCheckInvalidator != null) mCheckInvalidator.invalidate();
 
         if (shouldTriggerDelayedOnCreateInputConnection()) {
             triggerDelayedOnCreateInputConnection(view);
             return null;
         }
         if (DEBUG_LOGS) Log.w(TAG, "initializeAndGet: called from proxy view");
 
         if (mThreadedInputConnection == null) {
             if (DEBUG_LOGS) Log.w(TAG, "Creating ThreadedInputConnection...");
-            mThreadedInputConnection = new ThreadedInputConnection(view, imeAdapter, mHandler);
+            mThreadedInputConnection = new ThreadedInputConnection(view, imeAdapter, getHandler());
         } else {
             mThreadedInputConnection.resetOnUiThread();
         }
         return mThreadedInputConnection;
     }
 
     private void triggerDelayedOnCreateInputConnection(final View view) {
         if (DEBUG_LOGS) Log.w(TAG, "triggerDelayedOnCreateInputConnection");
         // Prevent infinite loop when View methods trigger onCreateInputConnection
         // on some OEM phones. (crbug.com/636197)
         if (mReentrantTriggering) return;
 
         // We need to check this before creating invalidator.
         if (!view.hasFocus()) return;
 
         mCheckInvalidator = new CheckInvalidator();
 
         if (!view.hasWindowFocus()) mCheckInvalidator.invalidate();
 
         // We cannot reuse the existing proxy view, if any, due to crbug.com/664402.
-        mProxyView = createProxyView(mHandler, view);
+        mProxyView = createProxyView(getHandler(), view);
 
         mReentrantTriggering = true;
         // This does not affect view focus of the real views.
         mProxyView.requestFocus();
         mReentrantTriggering = false;
 
         view.getHandler().post(new Runnable() {
             @Override
             public void run() {
                 // This is a hack to make InputMethodManager believe that the proxy view
                 // now has a focus. As a result, InputMethodManager will think that mProxyView
                 // is focused, and will call getHandler() of the view when creating input
                 // connection.
 
                 // Step 1: Set mProxyView as InputMethodManager#mNextServedView.
                 // This does not affect the real window focus.
                 mProxyView.onWindowFocusChanged(true);
 
                 // Step 2: Have InputMethodManager focus in on mNextServedView.
                 // As a result, IMM will call onCreateInputConnection() on mProxyView on the same
                 // thread as mProxyView.getHandler(). It will also call subsequent InputConnection
                 // methods on this IME thread.
                 mInputMethodManagerWrapper.isActive(view);
 
                 // Step 3: Check that the above hack worked.
                 // Do not check until activation finishes inside InputMethodManager (on IME thread).
-                mHandler.post(new Runnable() {
+                getHandler().post(new Runnable() {
                     @Override
                     public void run() {
                         postCheckRegisterResultOnUiThread(view, mCheckInvalidator,
                                 CHECK_REGISTER_RETRY);
                     }
                 });
             }
         });
     }
 
@@ skipping 35 matching lines @@
         mInputMethodUma.recordProxyViewSuccess();
     }
 
     @VisibleForTesting
     protected void onRegisterProxyViewFailure() {
         Log.w(TAG, "onRegisterProxyViewFailure");
         mInputMethodUma.recordProxyViewFailure();
     }
 
     @Override
-    public Handler getHandler() {
-        return mHandler;
-    }
-
-    @Override
     public void onWindowFocusChanged(boolean gainFocus) {
         if (DEBUG_LOGS) Log.d(TAG, "onWindowFocusChanged: " + gainFocus);
         if (!gainFocus && mCheckInvalidator != null) mCheckInvalidator.invalidate();
         if (mProxyView != null) mProxyView.onOriginalViewWindowFocusChanged(gainFocus);
     }
 
     @Override
     public void onViewFocusChanged(boolean gainFocus) {
         if (DEBUG_LOGS) Log.d(TAG, "onViewFocusChanged: " + gainFocus);
         if (!gainFocus && mCheckInvalidator != null) mCheckInvalidator.invalidate();
         if (mProxyView != null) mProxyView.onOriginalViewFocusChanged(gainFocus);
     }
 
     @Override
     public void onViewAttachedToWindow() {
         if (DEBUG_LOGS) Log.d(TAG, "onViewAttachedToWindow");
         if (mProxyView != null) mProxyView.onOriginalViewAttachedToWindow();
     }
 
     @Override
     public void onViewDetachedFromWindow() {
         if (DEBUG_LOGS) Log.d(TAG, "onViewDetachedFromWindow");
         if (mCheckInvalidator != null) mCheckInvalidator.invalidate();
         if (mProxyView != null) mProxyView.onOriginalViewDetachedFromWindow();
     }
 }