[sensors] Dispatch sensor events using postTask

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

Index: third_party/WebKit/Source/modules/sensor/Sensor.cpp
diff --git a/third_party/WebKit/Source/modules/sensor/Sensor.cpp b/third_party/WebKit/Source/modules/sensor/Sensor.cpp
index d5f1b0421b799ab73d20664171a2d3c7b609c7ee..e0f7f31f1146d45f0ef669607a5376bb909452c4 100644
--- a/third_party/WebKit/Source/modules/sensor/Sensor.cpp
+++ b/third_party/WebKit/Source/modules/sensor/Sensor.cpp
@@ -6,6 +6,7 @@
 
 #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"
@@ -263,8 +264,10 @@ void Sensor::pollForData()
     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();
 }
@@ -274,7 +277,11 @@ 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();
 }
 
@@ -297,4 +304,14 @@ void Sensor::updatePollingStatus()
     }
 }
 
+void Sensor::notifySensorReadingChanged()
+{
+    dispatchEvent(SensorReadingEvent::create(EventTypeNames::change, m_sensorReading));
+}
+
+void Sensor::notifyStateChanged()
+{
+    dispatchEvent(Event::create(EventTypeNames::statechange));
+}
+
 } // namespace blink