components/metrics/clean_exit_beacon.h

// Copyright 2014 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 COMPONENTS_METRICS_CLEAN_EXIT_BEACON_H_
#define COMPONENTS_METRICS_CLEAN_EXIT_BEACON_H_

#include "base/macros.h"
#include "base/strings/string16.h"
#include "base/time/time.h"

class PrefRegistrySimple;
class PrefService;

namespace metrics {

// Reads and updates a beacon used to detect whether the previous browser
// process exited cleanly.
class CleanExitBeacon {
 public:
  // Instantiates a CleanExitBeacon whose value is stored in |local_state|.
  // |local_state| must be fully initialized.
  // On Windows, |backup_registry_key| is used to store a backup of the beacon.
  // It is ignored on other platforms.
  CleanExitBeacon(
      const base::string16& backup_registry_key,
      PrefService* local_state);

  ~CleanExitBeacon();

  // Returns the original value of the beacon.
  bool exited_cleanly() const { return initial_value_; }

  // Returns the original value of the last live timestamp.
  base::Time browser_last_live_timestamp() const {
    return initial_browser_last_live_timestamp_;
  }

  // Writes the provided beacon value and updates the last live timestamp.
  void WriteBeaconValue(bool exited_cleanly);

  // Updates the last live timestamp.
  void UpdateLastLiveTimestamp();

  // Registers local state prefs used by this class.
  static void RegisterPrefs(PrefRegistrySimple* registry);

 private:
  PrefService* const local_state_;
  const bool initial_value_;

  // This is the value of the last live timestamp from local state at the
  // time of construction. It notes a timestamp from the previous browser
  // session when the browser was known to be alive.
  const base::Time initial_browser_last_live_timestamp_;
  const base::string16 backup_registry_key_;

  DISALLOW_COPY_AND_ASSIGN(CleanExitBeacon);
};

}  // namespace metrics

#endif  // COMPONENTS_METRICS_CLEAN_EXIT_BEACON_H_