[sensors] Generic Sensors Framework blink side

third_party/WebKit/Source/modules/sensor/SensorPollingStrategy.cpp

+// 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.
+
+#include "modules/sensor/SensorPollingStrategy.h"
+
+#include "platform/Timer.h"
+#include "wtf/CurrentTime.h"
+
+namespace blink {
+
+SensorPollingStrategy::SensorPollingStrategy(double frequency, std::unique_ptr<Function<void()>> func)
+    : m_frequency(frequency)
+    , m_pollFunc(std::move(func))
+{
+}
+
+class ContiniousSensorPollingStrategy : public SensorPollingStrategy {
+public:
+    DEFINE_INLINE_VIRTUAL_TRACE()
+    {
+        SensorPollingStrategy::trace(visitor);
+    }
+
+    ContiniousSensorPollingStrategy(double frequency, std::unique_ptr<Function<void()>> func)
+        : SensorPollingStrategy(frequency, std::move(func))
+        , m_timer(this, &ContiniousSensorPollingStrategy::pollForData) {}
+private:
+    // SensorPollingStrategy overrides.
+    void startPolling() override;
+    void stopPolling() override;
+
+    void pollForData(TimerBase*);
+
+    Timer<ContiniousSensorPollingStrategy> m_timer;
+};
+
+void ContiniousSensorPollingStrategy::startPolling()
+{
+    (*m_pollFunc)();
+    m_timer.startRepeating(1 / m_frequency, BLINK_FROM_HERE);

[timvolodine, 2016/09/01 19:02:06]

what happens if the sensor is notification only, i.e. does not have a frequency
like e.g. AmbientLight?

[timvolodine, 2016/09/01 19:02:06]

also maybe DCHECK(frequency>0) ?

[Mikhail, 2016/09/02 08:23:43]

Different polling strategy class OnChangeSensorPollingStrategy is to be taken.
'frequency' is the one given by user and AmbientLight sensor consideres it to
poll the data on platform side (notification is send however only when the data
are changed).

[Mikhail, 2016/09/02 08:23:43]

Done.

+}
+
+void ContiniousSensorPollingStrategy::stopPolling()
+{
+    m_timer.stop();
+}
+
+void ContiniousSensorPollingStrategy::pollForData(TimerBase*)
+{
+    (*m_pollFunc)();
+}
+
+class OnChangeSensorPollingStrategy : public SensorPollingStrategy {
+public:
+    DEFINE_INLINE_VIRTUAL_TRACE()
+    {
+        SensorPollingStrategy::trace(visitor);
+    }
+
+    OnChangeSensorPollingStrategy(double frequency, std::unique_ptr<Function<void()>> func)
+        : SensorPollingStrategy(frequency, std::move(func))
+        , m_timer(this, &OnChangeSensorPollingStrategy::pollForData)
+        , m_polling(false)
+        , m_lastPollingTimestamp(0.0) {}
+private:
+    // SensorPollingStrategy overrides.
+    void startPolling() override;
+    void stopPolling() override;
+    void onSensorReadingChanged() override;
+
+    void pollForData(TimerBase*);
+
+    Timer<OnChangeSensorPollingStrategy> m_timer;
+    bool m_polling;
+    double m_lastPollingTimestamp;
+};
+
+void OnChangeSensorPollingStrategy::startPolling()
+{
+    (*m_pollFunc)();
+    m_polling = true;

[timvolodine, 2016/09/01 19:02:06]

my understanding was that some sensors do not require polling at all? what is
the difference with continuous polling here?

[Mikhail, 2016/09/02 08:23:43]

Polling here means just refreshing a sensor reading value from the shared
buffer.
In case of "onchange" sensor type the reading is updated on the signal from the
platform side, however its own frequency is considered as well so that reading
is not updated more frequently than it was requested by the given 'frequency'
option.

[timvolodine, 2016/09/02 19:41:28]

In that case, could you pls add some comments with explanation about the
'capping' of notification updates depending on the frequency.

I actually wonder if this has any use-cases at this point. You could consider
making this an 'empty' class and add this more 'advanced' functionality later
(with some tests). Up to you though.

[Mikhail, 2016/09/05 10:26:27]

Done.

+}
+
+void OnChangeSensorPollingStrategy::stopPolling()
+{
+    m_polling = false;
+}
+
+void OnChangeSensorPollingStrategy::onSensorReadingChanged()
+{
+    if (!m_polling || m_timer.isActive())
+        return;
+    double pollingPeriod = 1 / m_frequency;
+    double elapsedTime = WTF::monotonicallyIncreasingTime() - m_lastPollingTimestamp;
+
+    if (elapsedTime >= pollingPeriod) {
+        m_lastPollingTimestamp = WTF::monotonicallyIncreasingTime();
+        (*m_pollFunc)();
+    } else {
+        m_timer.startOneShot(pollingPeriod - elapsedTime, BLINK_FROM_HERE);
+    }
+}
+
+void OnChangeSensorPollingStrategy::pollForData(TimerBase*)
+{
+    if (!m_polling)
+        return;
+    m_lastPollingTimestamp = WTF::monotonicallyIncreasingTime();
+    (*m_pollFunc)();
+}
+
+// static
+SensorPollingStrategy* SensorPollingStrategy::create(double frequency, std::unique_ptr<Function<void()>> func, device::mojom::blink::ReportingMode mode)
+{
+    if (mode == device::mojom::blink::ReportingMode::CONTINUOUS)
+        return new ContiniousSensorPollingStrategy(frequency, std::move(func));
+
+    return new OnChangeSensorPollingStrategy(frequency, std::move(func));
+}
+
+} // namespace blink