[sensors]: Introduce the Generic Sensor API.

third_party/WebKit/Source/modules/sensor/Sensor.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/Sensor.h"
+
+#include "core/dom/Document.h"
+#include "core/dom/ExceptionCode.h"
+#include "core/events/Event.h"
+
+#include "modules/sensor/SensorReading.h"
+
+namespace blink {
+
+Sensor::~Sensor()
+{
+}
+
+Sensor::Sensor(ExecutionContext* executionContext, const SensorOptions& sensorOptions)
+    : ActiveScriptWrappable(this)
+    , ActiveDOMObject(executionContext)
+    , PlatformEventController(toDocument(executionContext)->page())
+    , m_sensorState(SensorState::Idle)
+    , m_sensorReading(nullptr)
+    , m_sensorOptions(sensorOptions)
+{
+}
+
+// Getters
+String Sensor::state() const
+{
+    switch (m_sensorState) {
+    case SensorState::Idle:
+        return "idle";
+    case SensorState::Activating:
+        return "activating";
+    case SensorState::Active:
+        return "active";
+    case SensorState::Errored:
+        return "errored";
+    }
+    NOTREACHED();
+    return "idle";
+}
+
+SensorReading* Sensor::reading() const
+{
+    return m_sensorReading.get();
+}
+
+void Sensor::start(ScriptState* scriptState, ExceptionState& exceptionState)
+{
+    if (m_sensorState != SensorState::Idle && m_sensorState != SensorState::Errored) {
+        exceptionState.throwDOMException(InvalidStateError, "Invalid State: SensorState is not idle or errored");
+
+        // Avoid re-entrancy. sensor.start() inside 'onstatechange' event handler.
+        m_hasEventListener = false;
+        stopUpdating();
+
+        return;
+    }
+
+    updateState(SensorState::Activating);
+
+    // TODO(riju) : Add Permissions stuff later.
+
+    m_hasEventListener = true;
+    startUpdating();
+    updateState(SensorState::Active);

[timvolodine, 2016/05/26 15:49:01]

is this correct? startUpdating is async, so it could result in
SensorState::Errored. SensorState::Active should probably be set in
didUpdateData in deriving class.

there are also some implementation considerations depending on the spec:
startUpdating() may trigger a one-shot update if there is data already so one of
the questions could be whether onstatechange(active) should be guaranteed to
come before ondatachange..

[riju_, 2016/05/26 17:32:21]

No, removing the active statechange from here.
enforcing event order. need to check this with spec author, before we do the
onstatechange(active).

[timvolodine, 2016/05/27 18:40:57]

ok, could you pls add a TODO regarding this in order to not forget in the
future; something like "verify the correct order of onstatechange(active) and
the first onchange(event)"

[riju_, 2016/05/30 10:15:13]

Done.

+
+}
+
+void Sensor::stop(ScriptState* scriptState, ExceptionState& exceptionState)
+{
+    if (m_sensorState == SensorState::Idle || m_sensorState == SensorState::Errored) {
+        exceptionState.throwDOMException(InvalidStateError, "Invalid State: SensorState is either idle or errored");
+        return;
+    }
+
+    // Avoid re-entrancy. sensor.stop() inside 'onstatechange' event handler.
+    if (m_sensorState == SensorState::Activating) {

[timvolodine, 2016/05/26 15:49:01]

so this means that we cannot stop the sensor while it's "activating". what does
the spec say about this?

regarding reentrancy it may be easier to 'postTask' the state change dispatch,
e.g. like we do in PlatformEventController using a timer.

[riju_, 2016/05/26 17:32:20]

Wrongly done , fixing it.

+        exceptionState.throwDOMException(InvalidStateError, "Invalid State: SensorState Activating");
+        return;
+    }
+
+    m_hasEventListener = false;
+    stopUpdating();
+
+    m_sensorReading.clear();
+    updateState(SensorState::Idle);
+}
+
+void Sensor::updateState(SensorState newState)
+{
+    if (m_sensorState == newState)
+        return;
+
+    m_sensorState = newState;
+    dispatchEvent(Event::create(EventTypeNames::statechange));
+}
+
+void Sensor::suspend()
+{
+    m_hasEventListener = false;
+    stopUpdating();
+}
+
+void Sensor::resume()
+{
+    m_hasEventListener = true;
+    startUpdating();
+}
+
+void Sensor::stop()
+{
+    m_hasEventListener = false;
+    stopUpdating();
+}
+
+bool Sensor::hasPendingActivity() const
+{
+    // Prevent V8 from garbage collecting the wrapper object if there are
+    // event listeners attached to it.
+    return hasEventListeners();
+}
+
+DEFINE_TRACE(Sensor)
+{
+    ActiveDOMObject::trace(visitor);
+    EventTargetWithInlineData::trace(visitor);
+    PlatformEventController::trace(visitor);
+    visitor->trace(m_sensorReading);
+}
+
+} // namespace blink