[sensors] Android platform adaptation for Generic Sensor API

device/generic_sensor/android/java/src/org/chromium/device/sensors/PlatformSensor.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.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorEventListener;
+import android.os.Build;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.mojom.device.mojom.ReportingMode;
+
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+import java.util.List;
+
+/**
+ * Implementation of PlatformSensor that uses Android Sensor Framework. Lifetime is controlled by
+ * the device::PlatformSensorAndroid.
+ */
+@JNINamespace("device")
+public class PlatformSensor implements SensorEventListener, PlatformSensorNotifier {
+    private static final double MICROSECONDS_IN_SECOND = 1000000;
+    private static final double MILLISECONDS_IN_NANOSECOND = 0.000001d;
+
+    /**
+     * The SENSOR_FREQUENCY_NORMAL is defined as 5Hz which corresponds to a polling delay
+     * @see android.hardware.SensorManager.SENSOR_DELAY_NORMAL value that is defined as 200000
+     * microseconds.
+     */
+    private static final double SENSOR_FREQUENCY_NORMAL = 5.0d;
+
+    /**
+     * Identifier of device::PlatformSensorAndroid instance.
+     */
+    private long mNativePlatformSensorAndroid;
+
+    /**
+     * Shared buffer that is used to return data to the client.
+     */
+    private ByteBuffer mBuffer;
+
+    /**
+     * Buffer that is filled with sensor reading data and swapped into mBuffer.
+     */
+    private ByteBuffer mSensorReadingData;
+
+    /**
+     * Used for fetching sensor reading values and obtaining information about the sensor.
+     * @see android.hardware.Sensor
+     */
+    private final Sensor mSensor;
+
+    /**
+     * The minimum delay between two readings in microseconds that is supported by the sensor.
+     */
+    private final int mMinDelayUsec;
+
+    /**
+     * The number of sensor reading values required from the sensor.
+     */
+    private final int mReadingCount;
+
+    /**
+     * Frequncy that is currently used by the sensor for polling.
+     */
+    private double mCurrentPollingFrequency;
+
+    /**
+     * Provides shared SensorManager and event processing thread Handler to PlatformSensor objects.
+     */
+    private final PlatformSensorProvider mProvider;
+
+    /**
+     * Provides methods to notify native PlatformSensorAndroid.
+     */
+    private PlatformSensorNotifier mNotifier;
+
+    /**
+     * Creates new PlatformSensor.
+     *
+     * @param sensorType type of the sensor to be constructed. @see android.hardware.Sensor.TYPE_*
+     * @param readingCount number of sensor reading values required from the sensor.
+     * @param provider object that shares SensorManager and polling thread Handler with sensors.
+     */
+    public static PlatformSensor create(
+            int sensorType, int readingCount, PlatformSensorProvider provider) {
+        List<Sensor> sensors = provider.getSensorManager().getSensorList(sensorType);
+        if (sensors.isEmpty()) return null;
+        return new PlatformSensor(sensors.get(0), readingCount, provider);
+    }
+
+    protected PlatformSensor(Sensor sensor, int readingCount, PlatformSensorProvider provider) {
+        mReadingCount = readingCount;
+        mProvider = provider;
+        mSensor = sensor;
+        mMinDelayUsec = mSensor.getMinDelay();
+    }
+
+    /**
+     * Initializes PlatformSensor, called by native code.
+     *
+     * @param nativePlatformSensorAndroid identifier of device::PlatformSensorAndroid instance.
+     * @param buffer shared buffer that is used to return data to the client.
+     */
+    @CalledByNative
+    protected void initPlatformSensorAndroid(long nativePlatformSensorAndroid, ByteBuffer buffer) {

[Ted C, 2016/09/07 18:12:23]

looks like this one could be private

[shalamov, 2016/09/08 13:40:49]

I'm using it for unit tests, is there a way to make it private and still expose
for unit tests?

+        initPlatformSensorAndroid(this, nativePlatformSensorAndroid, buffer);
+    }
+
+    /**
+     * Initializes PlatformSensor.
+     *
+     * @param notifier object that is used to notify native device::PlatformSensorAndroid.
+     * @param nativePlatformSensorAndroid identifier of device::PlatformSensorAndroid instance.
+     * @param buffer shared buffer that is used to return data to the client.
+     */
+    protected void initPlatformSensorAndroid(
+            PlatformSensorNotifier notifier, long nativePlatformSensorAndroid, ByteBuffer buffer) {
+        assert nativePlatformSensorAndroid != 0;
+        assert buffer != null;
+        mNativePlatformSensorAndroid = nativePlatformSensorAndroid;
+        mNotifier = notifier;
+        mBuffer = buffer;
+        mSensorReadingData = ByteBuffer.allocate(mBuffer.capacity());
+        mSensorReadingData.order(ByteOrder.nativeOrder());
+    }
+
+    /**
+     * Fills shared buffer with sensor reading data, throws exception if number of received values
+     * is less than the number required for the PlatformSensor.
+     */
+    private void fillSensorReadingData(SensorEvent event, ByteBuffer buffer)
+            throws IllegalStateException {
+        if (event.values.length < mReadingCount) throw new IllegalStateException();
+        for (int i = 0; i < mReadingCount; ++i) {
+            buffer.putDouble(event.values[i]);
+        }
+    }
+
+    /**
+     * Returns reporting mode supported by the sensor.
+     *
+     * @return ReportingMode reporting mode.
+     */
+    @CalledByNative
+    protected int getReportingMode() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+            return mSensor.getReportingMode() == Sensor.REPORTING_MODE_CONTINUOUS
+                    ? ReportingMode.CONTINUOUS
+                    : ReportingMode.ON_CHANGE;
+        }
+        return ReportingMode.CONTINUOUS;
+    }
+
+    /**
+     * Returns default configuration supported by the sensor. Currently only frequency is supported.
+     *
+     * @return double frequency.
+     */
+    @CalledByNative
+    protected double getDefaultConfiguration() {
+        return SENSOR_FREQUENCY_NORMAL;
+    }
+
+    /**
+     * Requests sensor to start polling for data.
+     *
+     * @return boolean true if successful, false otherwise.
+     */
+    @CalledByNative
+    protected boolean startSensor(double frequency) {

[Ted C, 2016/09/07 18:12:23]

just to make sure the frequency is sanity checked for reasonable values at some
point during its pipeline?  Want to make sure the site can't pass -1 or some
ridiculously high frequency that kills your phone.

[shalamov, 2016/09/07 18:49:18]

It is checked on native side, during mojo  type conversion and in
PlatformSensorConfiguration
https://cs.chromium.org/chromium/src/device/generic_sensor/public/cpp/sensor_...
https://cs.chromium.org/chromium/src/device/generic_sensor/public/cpp/platfor...

+        // If we already polling hw with same frequency, do not restart the sensor.
+        if (mCurrentPollingFrequency == frequency) return true;
+
+        // Unregister old listener if polling frequency has changed.
+        unregisterListener();
+        mProvider.sensorStarted(this);
+        boolean sensorStarted = mProvider.getSensorManager().registerListener(
+                this, mSensor, getSamplingPeriod(frequency), mProvider.getHandler());
+
+        if (!sensorStarted) {
+            stopSensor();
+            return sensorStarted;
+        }
+
+        mCurrentPollingFrequency = frequency;

[Ted C, 2016/09/07 18:12:23]

any reason this is under the !sensorStarted check above?

[shalamov, 2016/09/07 18:49:18]

If sensor failed to start with given configuration, then
mCurrentPollingFrequency should not be equal to what was provided to
startSensor(), that was the reason why I moved it after.

+        return sensorStarted;
+    }
+
+    private void unregisterListener() {
+        // Do not unregister if current polling frequency is 0, not polling for data.
+        if (mCurrentPollingFrequency == 0) return;

[Ted C, 2016/09/07 18:12:23]

should we not be registering if frequency is 0 above?

[shalamov, 2016/09/07 18:49:18]

Native side will never provide 0 frequency, but I can add check if you want.

+        mProvider.getSensorManager().unregisterListener(this, mSensor);
+    }
+
+    /**
+     * Requests sensor to stop polling for data.
+     */
+    @CalledByNative
+    protected void stopSensor() {
+        unregisterListener();
+        mProvider.sensorStopped(this);
+        mCurrentPollingFrequency = 0;
+    }
+
+    /**
+     * Checks whether configuration is supported by the sensor. Currently only frequency is
+     * supported.
+     *
+     * @return boolean true if configuration is supported, false otherwise.
+     */
+    @CalledByNative
+    protected boolean checkSensorConfiguration(double frequency) {
+        return mMinDelayUsec <= getSamplingPeriod(frequency);
+    }
+
+    /**
+     * Converts frequency to sampling period in microseconds.
+     */
+    private int getSamplingPeriod(double frequency) {
+        return (int) ((1 / frequency) * MICROSECONDS_IN_SECOND);
+    }
+
+    @Override
+    public void sensorReadingChanged() {
+        nativeNotifyPlatformSensorReadingChanged(mNativePlatformSensorAndroid);
+    }
+
+    @Override
+    public void sensorError() {
+        nativeNotifyPlatformSensorError(mNativePlatformSensorAndroid);
+    }
+
+    /**
+     * Notifies native device::PlatformSensorAndroid when reading is changed.
+     */
+    protected native void nativeNotifyPlatformSensorReadingChanged(

[Ted C, 2016/09/07 18:12:23]

Should these be private?

Also, we put native methods at the bottom.

[shalamov, 2016/09/08 13:40:49]

Done.

+            long nativePlatformSensorAndroid);
+
+    /**
+     * Notifies native device::PlatformSensorAndroid when there is an error.
+     */
+    protected native void nativeNotifyPlatformSensorError(long nativePlatformSensorAndroid);
+
+    @Override
+    public void onAccuracyChanged(Sensor sensor, int accuracy) {}
+
+    @Override
+    public void onSensorChanged(SensorEvent event) {
+        try {
+            mSensorReadingData.mark();
+            // Convert timestamp from nanoseconds to milliseconds.
+            mSensorReadingData.putDouble(event.timestamp * MILLISECONDS_IN_NANOSECOND);
+            fillSensorReadingData(event, mSensorReadingData);
+
+            mSensorReadingData.reset();
+
+            mBuffer.mark();
+            mBuffer.put(mSensorReadingData);
+            mSensorReadingData.reset();
+            mBuffer.reset();
+
+            if (getReportingMode() == ReportingMode.ON_CHANGE) {
+                mNotifier.sensorReadingChanged();
+            }
+        } catch (BufferOverflowException | IllegalStateException e) {
+            mNotifier.sensorError();
+            stopSensor();
+        }
+    }
+}