net/base/network_time_notifier.h

   1 // Copyright (c) 2013 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 NET_BASE_NETWORK_TIME_NOTIFIER_H_
   6 #define NET_BASE_NETWORK_TIME_NOTIFIER_H_
   7
   8 #include <vector>
   9
  10 #include "base/callback.h"
  11 #include "base/memory/ref_counted.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "base/memory/weak_ptr.h"
  14 #include "base/threading/thread_checker.h"
  15 #include "base/time/tick_clock.h"
  16 #include "base/time/time.h"
  17 #include "net/base/net_export.h"
  18
  19 namespace net {
  20
  21 // A class that receives updates for and maintains network time. Network time
  22 // sources can pass updates through UpdateNetworkTime, and network time
  23 // consumers can register as observers. This class is not thread-safe.
  24 class NET_EXPORT NetworkTimeNotifier {
  25  public:
  26   // Callback for observers to receive network time updates.
  27   // The parameters are:
  28   // const base::Time& network_time - the new network time.
  29   // const base::TimeTicks& network_time_ticks - the ticks time that corresponds
  30   //     with |network_time|.
  31   // const base::TimeDelta& network_time_uncertainty - the uncertainty
  32   //     associated with the new network time.
  33   typedef base::Callback<void(const base::Time&,
  34                               const base::TimeTicks&,
  35                               const base::TimeDelta&)> ObserverCallback;
  36
  37   // Takes ownership of |tick_clock|.
  38   explicit NetworkTimeNotifier(scoped_ptr<base::TickClock> tick_clock);
  39   ~NetworkTimeNotifier();
  40
  41   // Calculates corresponding time ticks according to the given parameters and
  42   // notifies observers. The provided |network_time| is precise at the given
  43   // |resolution| and represent the time between now and up to |latency| +
  44   // (now - |post_time|) ago.
  45   void UpdateNetworkTime(const base::Time& network_time,
  46                          const base::TimeDelta& resolution,
  47                          const base::TimeDelta& latency,
  48                          const base::TimeTicks& post_time);
  49
  50   // |observer_callback| will invoked every time the network time is updated, or
  51   // if a network time is already available when AddObserver is called.
  52   void AddObserver(const ObserverCallback& observer_callback);
  53
  54  private:
  55   base::ThreadChecker thread_checker_;
  56
  57   // For querying current time ticks.
  58   scoped_ptr<base::TickClock> tick_clock_;
  59
  60   // The network time based on last call to UpdateNetworkTime().
  61   base::Time network_time_;
  62
  63   // The estimated local time from |tick_clock| that corresponds with
  64   // |network_time|. Assumes the actual network time measurement was performed
  65   // midway through the latency time, and does not account for suspect/resume
  66   // events since the network time was measured.
  67   // See UpdateNetworkTime(..) implementation for details.
  68   base::TimeTicks network_time_ticks_;
  69
  70   // Uncertainty of |network_time_| based on added inaccuracies/resolution.
  71   // See UpdateNetworkTime(..) implementation for details.
  72   base::TimeDelta network_time_uncertainty_;
  73
  74   // List of network time update observers.
  75   // A vector of callbacks is used, rather than an ObserverList, so that the
  76   // lifetime of the observer can be bound to the callback.
  77   std::vector<ObserverCallback> observers_;
  78
  79   DISALLOW_COPY_AND_ASSIGN(NetworkTimeNotifier);
  80 };
  81
  82 }  // namespace net
  83
  84 #endif  // NET_BASE_NETWORK_TIME_NOTIFIER_H_