components/network_time/network_time_tracker.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
   6 #define COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
   7
   8 #include "base/memory/scoped_ptr.h"
   9 #include "base/threading/thread_checker.h"
  10 #include "base/time/time.h"
  11
  12 class PrefRegistrySimple;
  13 class PrefService;
  14
  15 namespace base {
  16 class TickClock;
  17 }
  18
  19 namespace network_time {
  20
  21 // A class that receives network time updates and can provide the network time
  22 // for a corresponding local time. This class is not thread safe.
  23 class NetworkTimeTracker {
  24  public:
  25   static void RegisterPrefs(PrefRegistrySimple* registry);
  26
  27   NetworkTimeTracker(scoped_ptr<base::TickClock> tick_clock,
  28                      PrefService* pref_service);
  29   ~NetworkTimeTracker();
  30
  31   // Returns the network time corresponding to |time_ticks| if network time
  32   // is available. Returns false if no network time is available yet. Can also
  33   // return the error range if |uncertainty| isn't NULL.
  34   bool GetNetworkTime(base::TimeTicks time_ticks,
  35                       base::Time* network_time,
  36                       base::TimeDelta* uncertainty) const;
  37
  38   // Calculates corresponding time ticks according to the given parameters.
  39   // The provided |network_time| is precise at the given |resolution| and
  40   // represent the time between now and up to |latency| + (now - |post_time|)
  41   // ago.
  42   void UpdateNetworkTime(base::Time network_time,
  43                          base::TimeDelta resolution,
  44                          base::TimeDelta latency,
  45                          base::TimeTicks post_time);
  46
  47   bool received_network_time() const {
  48     return received_network_time_;
  49   }
  50
  51  private:
  52   // For querying current time ticks.
  53   scoped_ptr<base::TickClock> tick_clock_;
  54
  55   PrefService* pref_service_;
  56
  57   // Network time based on last call to UpdateNetworkTime().
  58   base::Time network_time_;
  59
  60   // The estimated local time from |tick_clock| that corresponds with
  61   // |network_time|. Assumes the actual network time measurement was performed
  62   // midway through the latency time, and does not account for suspect/resume
  63   // events since the network time was measured.
  64   // See UpdateNetworkTime(..) implementation for details.
  65   base::TimeTicks network_time_ticks_;
  66
  67   // Uncertainty of |network_time_| based on added inaccuracies/resolution.
  68   // See UpdateNetworkTime(..) implementation for details.
  69   base::TimeDelta network_time_uncertainty_;
  70
  71   base::ThreadChecker thread_checker_;
  72
  73   bool received_network_time_;
  74
  75   DISALLOW_COPY_AND_ASSIGN(NetworkTimeTracker);
  76 };
  77
  78 }  // namespace network_time
  79
  80 #endif  // COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_