accelerometer: Refactor AccelerometerFileReader

This commit simplifies the logic and puts only the blocking code in the
created USER_VISIBLE sequenced task runner. In this way, most of the
tasks are run on the UI thread.

BUG=b:175355860
TEST=run on octopus

Change-Id: I50b9380c5d0667513430f4f3b685317687be844d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586288
Commit-Queue: Cheng-Hao Yang <chenghaoyang@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839057}

ash/accelerometer/accelerometer_file_reader.h

@@ -11,7 +11,9 @@
 #include "ash/accelerometer/accelerometer_reader.h"
 #include "ash/public/cpp/tablet_mode_observer.h"
 #include "base/files/file_util.h"
-#include "base/observer_list_threadsafe.h"
+#include "base/observer_list.h"
+#include "base/sequence_checker.h"
+#include "base/timer/timer.h"
 
 namespace ash {
 
@@ -33,18 +35,10 @@ class AccelerometerFileReader : public AccelerometerProviderInterface,
   void StopListenToTabletModeController() override;
   void SetEmitEvents(bool emit_events) override;
 
-  // Attempts to read the accelerometer data. Upon success, converts the raw
-  // reading to an AccelerometerUpdate and notifies observers. Triggers another
-  // read at the current sampling rate.
-  void Read();
-
   // Controls accelerometer reading.
   void EnableAccelerometerReading();
   void DisableAccelerometerReading();
 
-  // Tracks if accelerometer initialization is completed.
-  void CheckInitStatus();
-
   // With ChromeOS EC lid angle driver present, it's triggered when the device
   // is physically used as a tablet (even thought its UI might be in clamshell
   // mode), cancelled otherwise.
@@ -55,6 +49,14 @@ class AccelerometerFileReader : public AccelerometerProviderInterface,
   void OnTabletPhysicalStateChanged() override;
 
  private:
+  struct InitializationResult {
+    InitializationResult();
+    ~InitializationResult();
+
+    State initialization_state;
+    ECLidAngleDriverStatus ec_lid_angle_driver_status;
+  };
+
   // Represents necessary information in order to read an accelerometer device.
   struct ReadingData {
     ReadingData();
@@ -95,18 +97,24 @@ class AccelerometerFileReader : public AccelerometerProviderInterface,
 
   ~AccelerometerFileReader() override;
 
-  // Detects the accelerometer configuration.
+  // Post a task to initialize on |task_runner_| and process the result on the
+  // UI thread. May be called multiple times in the retries.
+  void TryScheduleInitialize();
+
+  // Detects the accelerometer configuration in |task_runner_|.
   // If an accelerometer is available, it triggers reads.
   // This function MAY be called more than once.
   // This function contains the actual initialization code to be run by the
   // Initialize function. It is needed because on some devices the sensor hub
-  // isn't available at the time the call to Initialize is made. If the sensor
-  // is found to be missing we'll make a call to TryScheduleInitializeInternal.
-  void InitializeInternal();
+  // isn't available at the time the call to Initialize is made.
+  // If the sensor is found to be missing we'll request a re-run of this
+  // function by returning State::INITIALIZING. TryScheduleInitializeInternal.
+  InitializationResult InitializeInternal();
 
-  // Attempt to reschedule a run of InitializeInternal(). The function will be
-  // scheduled to run again if Now() < initialization_timeout_.
-  void TryScheduleInitializeInternal();
+  // Attempt to finish the initialization with the result state. If it's
+  // State::INITIALIZING, it means something is missing and need to re-run
+  // |TryScheduleInitialize|, if not timed out yet.
+  void SetStatesWithInitializationResult(InitializationResult result);
 
   // When accelerometers are presented as separate iio_devices this will perform
   // the initialize for one of the devices, at the given |iio_path| and the
@@ -122,14 +130,10 @@ class AccelerometerFileReader : public AccelerometerProviderInterface,
   bool InitializeLegacyAccelerometers(const base::FilePath& iio_path,
                                       const base::FilePath& name);
 
-  // Attempts to read the accelerometer data. Upon a success, converts the raw
-  // reading to an AccelerometerUpdate and notifies observers.
-  void ReadFileAndNotify();
-
-  void SetEmitEventsInternal(bool emit_events);
-
-  // True if periodical accelerometer read is on.
-  bool accelerometer_read_on_ = false;
+  // Attempts to read the accelerometer data in |task_runner_|. Upon a success,
+  // converts the raw reading to an AccelerometerUpdate and notifies observers.
+  void ReadSample();
+  void NotifyObserversWithUpdate(scoped_refptr<AccelerometerUpdate> update);
 
   bool emit_events_ = true;
 
@@ -137,17 +141,24 @@ class AccelerometerFileReader : public AccelerometerProviderInterface,
   base::TimeTicks initialization_timeout_;
 
   // The accelerometer configuration.
-  ConfigurationData configuration_;
+  // Only used in |blocking_task_runner_|.
+  ConfigurationData configuration_ GUARDED_BY_CONTEXT(sequence_checker_);
+
+  // The timer to repeatedly read samples.
+  // Only used in |blocking_task_runner_|.
+  base::RepeatingTimer read_refresh_timer_
+      GUARDED_BY_CONTEXT(sequence_checker_);
 
   // The observers to notify of accelerometer updates.
-  scoped_refptr<base::ObserverListThreadSafe<AccelerometerReader::Observer>>
-      observers_;
+  base::ObserverList<AccelerometerReader::Observer>::Unchecked observers_;
 
   // The task runner to use for blocking tasks.
-  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+  scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
+
+  // The task runner of the UI thread.
+  scoped_refptr<base::SequencedTaskRunner> ui_task_runner_;
 
-  // The last seen accelerometer data.
-  scoped_refptr<AccelerometerUpdate> update_;
+  SEQUENCE_CHECKER(sequence_checker_);
 };
 
 }  // namespace ash

ash/accelerometer/accelerometer_reader.h

@@ -25,8 +25,15 @@ enum class ECLidAngleDriverStatus { UNKNOWN, SUPPORTED, NOT_SUPPORTED };
 
 class AccelerometerProviderInterface;
 
-// Reads an accelerometer device and reports data back to an
-// AccelerometerDelegate.
+// AccelerometerReader should only be used on the UI thread.
+// It notifies observers if EC Lid Angle Driver is supported, and provides
+// accelerometers' (lid and base) samples.
+// The current usages of accelerometers' samples are for calculating the angle
+// between the lid and the base, which can be substituted by EC Lid Angle
+// Driver, if it exists, and the auto rotation, which only needs
+// lid-accelerometer's data.
+// Therefore, if EC Lid Angle Driver is present, base-accelerometer's samples
+// may be ignored and not sent to the observers.
 class ASH_EXPORT AccelerometerReader {
  public:
   // An interface to receive data from the AccelerometerReader.