[sensors] Android platform adaptation for Generic Sensor API

device/generic_sensor/android/java/src/org/chromium/device/sensors/PlatformSensorProvider.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.device.sensors;
+
+import android.content.Context;
+import android.hardware.Sensor;
+import android.hardware.SensorManager;
+import android.os.Build;
+import android.os.Handler;
+import android.os.HandlerThread;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+import org.chromium.mojom.device.mojom.SensorType;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Lifetime is controlled by device::PlatformSensorProviderAndroid.
+ */
+@JNINamespace("device")
+class PlatformSensorProvider {
+    /**
+     * SensorManager that is shared among PlatformSensor objects. It is used for Sensor object
+     * creation and @see android.hardware.SensorEventListener registration.
+     * @see android.hardware.SensorManager
+     */
+    private final SensorManager mSensorManager;
+
+    /**
+     * Thread that is handling all sensor events.
+     */
+    private HandlerThread mSensorsThread;
+
+    /**
+     * Processes messages on #mSensorsThread message queue. Provided to #mSensorManager when
+     * sensor should start polling for data.
+     */
+    private Handler mHandler;
+
+    /**
+     * Set of currently active PlatformSensor objects.
+     */
+    private final Set<PlatformSensor> mActiveSensors = new HashSet<PlatformSensor>();
+
+    /**
+     * Returns shared thread Handler.
+     *
+     * @return Handler thread handler.
+     */
+    public Handler getHandler() {
+        return mHandler;
+    }
+
+    /**
+     * Returns shared SensorManager.
+     *
+     * @return SensorManager sensor manager.
+     */
+    public SensorManager getSensorManager() {
+        return mSensorManager;
+    }
+
+    /**
+     * Notifies PlatformSensorProvider that sensor started polling for data. Adds sensor to
+     * a set of active sensors, creates and starts new thread if needed.
+     */
+    public void sensorStarted(PlatformSensor sensor) {
+        mActiveSensors.add(sensor);
+        if (mSensorsThread == null) {
+            mSensorsThread = new HandlerThread("SensorsHandlerThread");
+            mSensorsThread.start();
+            mHandler = new Handler(mSensorsThread.getLooper());
+        }
+    }
+
+    /**
+     * Notifies PlatformSensorProvider that sensor is no longer polling for data. When
+     * #mActiveSensors becomes empty thread is stopped.
+     */
+    public void sensorStopped(PlatformSensor sensor) {
+        mActiveSensors.remove(sensor);
+        if (mActiveSensors.isEmpty() && mSensorsThread != null) {
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
+                mSensorsThread.quitSafely();
+            } else {
+                mSensorsThread.quit();
+            }
+
+            mSensorsThread = null;
+            mHandler = null;
+        }
+    }
+
+    private PlatformSensorProvider(Context context) {
+        mSensorManager = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
+    }
+
+    /**
+     * Creates PlatformSensorProvider instance.
+     *
+     * @param context application context.
+     * @return PlatformSensorProvider new PlatformSensorProvider instance.
+     */
+    @CalledByNative
+    protected static PlatformSensorProvider create(Context context) {
+        return new PlatformSensorProvider(context);
+    }
+
+    /**
+     * Creates PlatformSensor instance.
+     *
+     * @param type type of a sensor.
+     * @return PlatformSensor new PlatformSensor instance or null if sensor cannot be created.
+     */
+    @CalledByNative
+    protected PlatformSensor createSensor(int type) {
+        if (mSensorManager == null) return null;
+
+        switch (type) {
+            case SensorType.AMBIENT_LIGHT:
+                return PlatformSensor.create(Sensor.TYPE_LIGHT, 1, this);
+            case SensorType.ACCELEROMETER:
+                return PlatformSensor.create(Sensor.TYPE_ACCELEROMETER, 3, this);
+            case SensorType.LINEAR_ACCELERATION:
+                return PlatformSensor.create(Sensor.TYPE_LINEAR_ACCELERATION, 3, this);
+            case SensorType.GYROSCOPE:
+                return PlatformSensor.create(Sensor.TYPE_GYROSCOPE, 3, this);
+            case SensorType.MAGNETOMETER:
+                return PlatformSensor.create(Sensor.TYPE_MAGNETIC_FIELD, 3, this);
+            default:
+                return null;
+        }
+    }
+}