[chromeos] New PowerManagerClient observer to collect power data.

chromeos/power/power_data_collector.h

Index: chromeos/power/power_data_collector.h
diff --git a/chromeos/power/power_data_collector.h b/chromeos/power/power_data_collector.h
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+// Copyright (c) 2013 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.
+
+#ifndef CHROMEOS_POWER_POWER_DATA_COLLECTOR_H_
+#define CHROMEOS_POWER_POWER_DATA_COLLECTOR_H_
+
+#include <vector>
+
+#include "base/gtest_prod_util.h"
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "chromeos/dbus/power_manager_client.h"
+
+namespace power_manager {
+class PowerSupplyProperties;
+}
+
+namespace chromeos {
+
+// A class which starts collecting power metrics, like the battery charge, as
+// soon as it is initialized via Initialize().
+//
+// The constructor for this class is private as we want only a single global
+// instance to be created via Initialize(). Also, Initialize() should be called
+// only after the DBusThreadManager is initialized. The single global instance
+// should be destroyed via Shutdown(), and before the DBusThreadManager is
+// shutdown.

[stevenjb, 2013/12/11 20:54:37]

This paragraph could be simplified, e.g.: "This class is implemented as a global
singleton, initialized after DBusThreadManager which it depends on."

(The details are already sufficiently commented with each method)

[Siva Chandra, 2013/12/11 21:30:56]

Done.

+class PowerDataCollector
+    : public PowerManagerClient::Observer,
+      public base::RefCountedThreadSafe<PowerDataCollector> {
+ public:
+  struct PowerSupplySnapshot {
+    // Generated by TimeTicks::Now.

[stevenjb, 2013/12/11 20:54:37]

Describe what this represents (the time of the snapshot) not the implementation.

[Siva Chandra, 2013/12/11 21:30:56]

Done.

+    base::TimeTicks time;
+
+    // true if connected to external power at the time of the snapshot.

[stevenjb, 2013/12/11 20:54:37]

True

[Siva Chandra, 2013/12/11 21:30:56]

Done.

+    bool external_power;
+
+    // The battery charge as a percentage of full charge in range [0.0, 100.00].
+    double battery_charge;
+  };
+
+ public:
+  // Can be called only after DBusThreadManager is initialized.
+  static void Initialize();
+
+  // Can be called only if initialized via Initialize, and before
+  // DBusThreadManager is destroyed.
+  static void Shutdown();
+
+  // Returns the global instance of PowerDataCollector.
+  static PowerDataCollector *Get();
+
+  // Call this when processing the power supply data received from
+  // GetPowerSupplyData. Call UnlockPowerSupplyData after done with processing.
+  void LockPowerSupplyData(void);
+
+  // Returns a reference to a vector of power supply data. Invoke this function
+  // after locking the data with LockPowerSupplyData, and unlock after done
+  // processing the data with UnlockPowerSupplyData.
+  std::vector<PowerSupplySnapshot> &GetPowerSupplyData(void);

[stevenjb, 2013/12/11 20:54:37]

I don't think we should introduce a lock just to avoid a copy, but also I don't
expect you will actually need to access this from anything except the UI thread.
(The PowerManagerClient::Observer will all be called on the UI thread).

[Siva Chandra, 2013/12/11 21:30:56]

Done.

+
+  // Call this after done with processing the power supply data got from
+  // &GetPowerSupplyData.
+  void UnlockPowerSupplyData(void);
+
+ private:
+  friend class base::RefCountedThreadSafe<PowerDataCollector>;
+  friend class PowerDataCollectorTest;
+  FRIEND_TEST_ALL_PREFIXES(PowerDataCollectorTest, AppendPowerSupplySnapshot);
+
+  // When the 'testing' argument is 'true', the instance is created without
+  // checking for an initialized DBusThreadManager and hence it does not listen
+  // to any PowerManagerClient notifications.
+  explicit PowerDataCollector(const bool testing);
+
+  virtual ~PowerDataCollector() {}
+
+  // Used in tests. Initializes the PowerDataCollector so that unit tests
+  // can be performed without depending on the DBusThreadManager.
+  static void InitializeTesting();
+
+  void AppendPowerSupplySnapshot(const PowerSupplySnapshot& snapshot);
+  void ShutdownInstance(void);
+
+  // PowerManagerClient::Observer implementation:
+  virtual void PowerChanged(
+      const power_manager::PowerSupplyProperties& prop) OVERRIDE;
+
+ private:
+  // Is true for testing instance.
+  bool testing_;
+
+  base::Lock power_supply_lock_;
+  std::vector<PowerSupplySnapshot> power_supply_;
+
+  DISALLOW_COPY_AND_ASSIGN(PowerDataCollector);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_POWER_POWER_DATA_COLLECTOR_H_