DeviceOrientationEventPump: simplify fallback logic

Change-Id: Ie9b1c8d4b928e7328ecd8efd2139c0ba3f543261
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2217752Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#773575}

third_party/blink/renderer/modules/device_orientation/device_orientation_event_pump.cc

@@ -47,9 +47,7 @@ const double DeviceOrientationEventPump::kOrientationThreshold = 0.1;
 DeviceOrientationEventPump::DeviceOrientationEventPump(
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,
     bool absolute)
-    : DeviceSensorEventPump(std::move(task_runner)),
-      absolute_(absolute),
-      fall_back_to_absolute_orientation_sensor_(!absolute) {
+    : DeviceSensorEventPump(std::move(task_runner)), absolute_(absolute) {
   relative_orientation_sensor_ = MakeGarbageCollected<DeviceSensorEntry>(
       this, device::mojom::SensorType::RELATIVE_ORIENTATION_EULER_ANGLES);
   absolute_orientation_sensor_ = MakeGarbageCollected<DeviceSensorEntry>(
@@ -97,8 +95,10 @@ void DeviceOrientationEventPump::SendStartMessage(LocalFrame& frame) {
   if (absolute_) {
     absolute_orientation_sensor_->Start(sensor_provider_.get());
   } else {
-    fall_back_to_absolute_orientation_sensor_ = true;
-    should_suspend_absolute_orientation_sensor_ = false;
+    // Start() is asynchronous. Therefore IsConnected() can not be checked right
+    // away to determine if we should attempt to fall back to
+    // absolute_orientation_sensor_.
+    attempted_to_fall_back_to_absolute_orientation_sensor_ = false;
     relative_orientation_sensor_->Start(sensor_provider_.get());
   }
 }
@@ -109,22 +109,8 @@ void DeviceOrientationEventPump::SendStopMessage() {
   // the event listener is more rare than the page visibility changing,
   // Sensor::Suspend() is used to optimize this case for not doing extra work.
 
-  relative_orientation_sensor_->Stop();
-  // This is needed in case we fallback to using the absolute orientation
-  // sensor. In this case, the relative orientation sensor is marked as
-  // SensorState::SHOULD_SUSPEND, and if the relative orientation sensor
-  // is not available, the absolute orientation sensor should also be marked as
-  // SensorState::SHOULD_SUSPEND, but only after the
-  // absolute_orientation_sensor_.Start() is called for initializing
-  // the absolute orientation sensor in
-  // DeviceOrientationEventPump::DidStartIfPossible().
-  if (relative_orientation_sensor_->state() ==
-          DeviceSensorEntry::State::SHOULD_SUSPEND &&
-      fall_back_to_absolute_orientation_sensor_) {
-    should_suspend_absolute_orientation_sensor_ = true;
-  }
-
   absolute_orientation_sensor_->Stop();
+  relative_orientation_sensor_->Stop();
 
   // Reset the cached data because DeviceOrientationDispatcher resets its
   // data when stopping. If we don't reset here as well, then when starting back
@@ -148,18 +134,23 @@ void DeviceOrientationEventPump::FireEvent(TimerBase*) {
 }
 
 void DeviceOrientationEventPump::DidStartIfPossible() {
-  if (!absolute_ && !relative_orientation_sensor_->IsConnected() &&
-      fall_back_to_absolute_orientation_sensor_ && sensor_provider_) {
-    // When relative orientation sensor is not available fall back to using
-    // the absolute orientation sensor but only on the first failure.
-    fall_back_to_absolute_orientation_sensor_ = false;
+  if (!absolute_ && sensor_provider_ &&
+      !relative_orientation_sensor_->IsConnected() &&
+      !attempted_to_fall_back_to_absolute_orientation_sensor_) {
+    // If relative_orientation_sensor_ was requested but was not able to connect
+    // then fall back to using absolute_orientation_sensor_.
+    attempted_to_fall_back_to_absolute_orientation_sensor_ = true;
     absolute_orientation_sensor_->Start(sensor_provider_.get());
-    if (should_suspend_absolute_orientation_sensor_) {
-      // The absolute orientation sensor needs to be marked as
-      // SensorState::SUSPENDED when it is successfully initialized.
+    if (relative_orientation_sensor_->state() ==
+        DeviceSensorEntry::State::SHOULD_SUSPEND) {
+      // If SendStopMessage() was called before the OnSensorCreated() callback
+      // registered that relative_orientation_sensor_ was not able to connect
+      // then absolute_orientation_sensor_ needs to be Stop()'d so that it
+      // matches the relative_orientation_sensor_ state.
       absolute_orientation_sensor_->Stop();
-      should_suspend_absolute_orientation_sensor_ = false;
     }
+    // Start() is asynchronous. Give the OnSensorCreated() callback time to fire
+    // before calling DeviceSensorEventPump::DidStartIfPossible().
     return;
   }
   DeviceSensorEventPump::DidStartIfPossible();

third_party/blink/renderer/modules/device_orientation/device_orientation_event_pump.h

@@ -65,8 +65,9 @@ class MODULES_EXPORT DeviceOrientationEventPump
   bool ShouldFireEvent(const DeviceOrientationData* data) const;
 
   bool absolute_;
-  bool fall_back_to_absolute_orientation_sensor_;
-  bool should_suspend_absolute_orientation_sensor_ = false;
+  // If relative_orientation_sensor_ is requested but fails to initialize then
+  // attempt to fall back to absolute_orientation_sensor_ once.
+  bool attempted_to_fall_back_to_absolute_orientation_sensor_;
   Member<DeviceOrientationData> data_;
   Member<PlatformEventController> controller_;