Java-side sensor polling getHandler() method simplification as per joth's comment.

content/public/android/java/src/org/chromium/content/browser/DeviceMotionAndOrientation.java

 // Copyright (c) 2013 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;
 
 import android.content.Context;
 import android.hardware.Sensor;
 import android.hardware.SensorEvent;
 import android.hardware.SensorEventListener;
 import android.hardware.SensorManager;
 import android.os.Handler;
+import android.os.HandlerThread;
 import android.os.Looper;
 import android.util.Log;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 
 import org.chromium.base.CalledByNative;
 import org.chromium.base.JNINamespace;
 import org.chromium.base.WeakContext;
@@ skipping 328 matching lines @@
 
     protected void gotRotationRate(double alpha, double beta, double gamma) {
         synchronized (mNativePtrLock) {
             if (mNativePtr != 0) {
               nativeGotRotationRate(mNativePtr, alpha, beta, gamma);
             }
         }
     }
 
     private Handler getHandler() {
+        // TODO(timvolodine): Remove the mHandlerLock when sure that getHandler is not called
+        // from multiple threads. This will be the case when device motion and device orientation
+        // use the same polling thread (also see crbug/234282).
         synchronized (mHandlerLock) {
-            // If we don't have a background thread, start it now.
-            if (mThread == null) {
-                mThread = new Thread(new Runnable() {
-                    @Override
-                    public void run() {
-                        Looper.prepare();
-                        // Our Handler doesn't actually have to do anything, because
-                        // SensorManager posts directly to the underlying Looper.
-                        setHandler(new Handler());
-                        Looper.loop();
-                    }
-                });
-                mThread.start();
-            }
-            // Wait for the background thread to spin up.
-            while (mHandler == null) {
-                try {
-                    mHandlerLock.wait();
-                } catch (InterruptedException e) {
-                    // Somebody doesn't want us to wait! That's okay, SensorManager accepts null.
-                    return null;
-                }
+            if (mHandler == null) {
+                HandlerThread thread = new HandlerThread("DeviceMotionAndOrientation");
+                thread.start();
+                mHandler = new Handler(thread.getLooper());  // blocks on thread start
             }
             return mHandler;
         }
     }
 
-    private void setHandler(Handler handler) {
-        synchronized (mHandlerLock) {
-            mHandler = handler;
-            mHandlerLock.notify();
-        }
-    }
-
     @CalledByNative
     static DeviceMotionAndOrientation getInstance() {
         synchronized (sSingletonLock) {
             if (sSingleton == null) {
                 sSingleton = new DeviceMotionAndOrientation();
             }
             return sSingleton;
         }
     }
 
@@ skipping 57 matching lines @@
 
         public void unregisterListener(SensorEventListener listener, int sensorType) {
             List<Sensor> sensors = mSensorManager.getSensorList(sensorType);
             if (!sensors.isEmpty()) {
                 mSensorManager.unregisterListener(listener, sensors.get(0));
             }
         }
     }
 
 }