Simplify handler initialization for InputConnectionFactory

As a follow-up to https://codereview.chromium.org/2543893002/,
we make the code easy to read and remove unnecessary findbug suppression.

BUG=668692

Review-Url: https://codereview.chromium.org/2544163003
Cr-Commit-Position: refs/heads/master@{#436218}

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

@@ -11,7 +11,6 @@ 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
@@ -31,11 +30,6 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
     // 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;
@@ -43,6 +37,18 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
     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 {
@@ -61,19 +67,12 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
 
     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
@@ -133,7 +132,7 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
 
         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();
         }
@@ -154,7 +153,7 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
         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.
@@ -181,7 +180,7 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
 
                 // 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,
@@ -236,11 +235,6 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
         mInputMethodUma.recordProxyViewFailure();
     }
 
-    @Override
-    public Handler getHandler() {
-        return mHandler;
-    }
-
     @Override
     public void onWindowFocusChanged(boolean gainFocus) {
         if (DEBUG_LOGS) Log.d(TAG, "onWindowFocusChanged: " + gainFocus);

content/public/android/junit/src/org/chromium/content/browser/input/ThreadedInputConnectionFactoryTest.java

@@ -58,13 +58,6 @@ public class ThreadedInputConnectionFactoryTest {
             super(inputMethodManagerWrapper);
         }
 
-        @Override
-        protected Handler createHandler() {
-            mImeHandler = super.createHandler();
-            mImeShadowLooper = (ShadowLooper) ShadowExtractor.extract(mImeHandler.getLooper());
-            return mImeHandler;
-        }
-
         @Override
         protected ThreadedInputConnectionProxyView createProxyView(Handler handler,
                 View containerView) {
@@ -135,6 +128,8 @@ public class ThreadedInputConnectionFactoryTest {
 
         mFactory = new TestFactory(new InputMethodManagerWrapper(mContext));
         mFactory.onWindowFocusChanged(true);
+        mImeHandler = mFactory.getHandler();
+        mImeShadowLooper = (ShadowLooper) ShadowExtractor.extract(mImeHandler.getLooper());
 
         when(mContext.getSystemService(Context.INPUT_METHOD_SERVICE))
                 .thenReturn(mInputMethodManager);