[Sensors] Fix reading updates after page refresh

third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.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/SensorReadingUpdater.h"
 
 #include "core/dom/Document.h"
 #include "device/generic_sensor/public/interfaces/sensor.mojom-blink.h"
 #include "modules/sensor/SensorProxy.h"
 #include "wtf/CurrentTime.h"
 
 using device::mojom::blink::ReportingMode;
 
 namespace blink {
 
 SensorReadingUpdater::SensorReadingUpdater(SensorProxy* sensorProxy)
     : m_sensorProxy(sensorProxy), m_hasPendingAnimationFrameTask(false) {}
 
 void SensorReadingUpdater::enqueueAnimationFrameTask() {
+  if (!m_document || m_document->isDetached()) {

[haraken, 2017/01/25 18:20:06]

Will the following work?

- Make SensorReadingUpdater inherit from ContextClient
- Use if(!getExecutionContext()) here.

[Mikhail, 2017/01/26 06:19:59]

As far as I see, ContextClient contains ExecutionContext instance which can be
set only once at construction, so inheriting from it would require re-creation
of the SensorReadingUpdater instance every time the context is detached,
further, we'd need to introduce a notification mechanism (or just a similar
SensorReadingUpdater  state checking) on the upper level to be aware if the
current SensorReadingUpdater instance must be re-created.
Considering all above the current approach IMO looks simpler.

+    // If the document has detached the scheduled callbacks
+    // will never be called.
+    m_hasPendingAnimationFrameTask = false;
+    m_document = m_sensorProxy->document();

[haraken, 2017/01/25 18:20:06]

Can we set m_document in SensorReadingUpdater's constructor?

Once you make SensorReadingUpdater inherit from ContextClient, it won't be
needed though.

[Mikhail, 2017/01/26 06:19:59]

Done.

+    if (!m_document)
+      return;
+  }
+
   if (m_hasPendingAnimationFrameTask)
     return;
 
   auto callback = WTF::bind(&SensorReadingUpdater::onAnimationFrame,
                             wrapWeakPersistent(this));
-  m_sensorProxy->document()->enqueueAnimationFrameTask(std::move(callback));
+  m_document->enqueueAnimationFrameTask(std::move(callback));
   m_hasPendingAnimationFrameTask = true;
 }
 
 void SensorReadingUpdater::start() {
   enqueueAnimationFrameTask();
 }
 
 void SensorReadingUpdater::onAnimationFrame() {
   m_hasPendingAnimationFrameTask = false;
   onAnimationFrameInternal();
 }
 
 DEFINE_TRACE(SensorReadingUpdater) {
+  visitor->trace(m_document);
   visitor->trace(m_sensorProxy);
 }
 
 class SensorReadingUpdaterContinuous : public SensorReadingUpdater {
  public:
   explicit SensorReadingUpdaterContinuous(SensorProxy* sensorProxy)
       : SensorReadingUpdater(sensorProxy) {}
 
   DEFINE_INLINE_VIRTUAL_TRACE() { SensorReadingUpdater::trace(visitor); }
 
@@ skipping 54 matching lines @@
 
 // static
 SensorReadingUpdater* SensorReadingUpdater::create(SensorProxy* proxy,
                                                    ReportingMode mode) {
   if (mode == ReportingMode::CONTINUOUS)
     return new SensorReadingUpdaterContinuous(proxy);
   return new SensorReadingUpdaterOnChange(proxy);
 }
 
 }  // namespace blink