[sensors] Dispatch sensor events using postTask

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/dom/ExecutionContextTask.h"
 #include "core/inspector/ConsoleMessage.h"
 #include "device/generic_sensor/public/interfaces/sensor.mojom-blink.h"
 #include "modules/sensor/SensorErrorEvent.h"
 #include "modules/sensor/SensorPollingStrategy.h"
 #include "modules/sensor/SensorProviderProxy.h"
 #include "modules/sensor/SensorReading.h"
 #include "modules/sensor/SensorReadingEvent.h"
 
 using namespace device::mojom::blink;
 
@@ skipping 237 matching lines @@
         DCHECK(m_polling);
         m_polling->stopPolling();
         return;
     }
 
     DCHECK(m_sensorProxy);
     DCHECK(m_sensorProxy->isInitialized());
     m_sensorProxy->updateInternalReading();
 
     DCHECK(m_sensorReading);
-    if (m_sensorReading->isReadingUpdated(m_storedData))
-        dispatchEvent(SensorReadingEvent::create(EventTypeNames::change, m_sensorReading));
+    if (getExecutionContext() && m_sensorReading->isReadingUpdated(m_storedData)) {
+        getExecutionContext()->postTask(BLINK_FROM_HERE,
+            createSameThreadTask(&Sensor::notifySensorReadingChanged, wrapWeakPersistent(this)));

[haraken, 2016/09/30 13:26:45]

wrapWeakPersistent means that the event may not be dispatched if the Sensor
object is gc-ed before the posted task runs. Is that okay?

[shalamov, 2016/09/30 13:51:44]

Yes, that was intentional. If sensor goes out of scope and gc-ed, posted tasks
should not keep sensor object alive. That could happen when JS wrapper goes out
of scope and there are no event listeners for the sensor object.

+    }
 
     m_storedData = m_sensorProxy->reading();
 }
 
 void Sensor::updateState(Sensor::SensorState newState)
 {
     if (newState == m_state)
         return;
     m_state = newState;
-    dispatchEvent(Event::create(EventTypeNames::statechange));
+    if (getExecutionContext()) {
+        getExecutionContext()->postTask(BLINK_FROM_HERE,
+            createSameThreadTask(&Sensor::notifyStateChanged, wrapWeakPersistent(this)));
+    }
+
     updatePollingStatus();
 }
 
 void Sensor::reportError()
 {
     updateState(Sensor::SensorState::ERRORED);
     // TODO(Mikhail) : Dispatch Sensor Error event.
 }
 
 void Sensor::updatePollingStatus()
 {
     if (!m_polling)
         return;
 
     if (m_state != Sensor::SensorState::ACTIVE
         || page()->visibilityState() != PageVisibilityStateVisible) {
         m_polling->stopPolling();
     } else {
         m_polling->startPolling();
     }
 }
 
+void Sensor::notifySensorReadingChanged()
+{
+    dispatchEvent(SensorReadingEvent::create(EventTypeNames::change, m_sensorReading));
+}
+
+void Sensor::notifyStateChanged()
+{
+    dispatchEvent(Event::create(EventTypeNames::statechange));
+}
+
 } // namespace blink