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 #include "net/base/network_time_notifier.h"
6
7 #include "base/basictypes.h"
8 #include "base/bind.h"
9 #include "base/i18n/time_formatting.h"
10 #include "base/location.h"
11 #include "base/message_loop/message_loop.h"
12 #include "base/stl_util.h"
13 #include "base/strings/utf_string_conversions.h"
14
15 namespace {
16
17 // Clock resolution is platform dependent.
18 #if defined(OS_WIN)
19 const int64 kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs;
20 #else
21 const int64 kTicksResolutionMs = 1; // Assume 1ms for non-windows platforms.
22 #endif
23
24 // Number of time measurements performed in a given network time calculation.
25 const int kNumTimeMeasurements = 5;
26
27 } // namespace
28
29 namespace net {
30
NetworkTimeNotifier(scoped_ptr<base::TickClock> tick_clock)31 NetworkTimeNotifier::NetworkTimeNotifier(
32 scoped_ptr<base::TickClock> tick_clock) {
33 tick_clock_ = tick_clock.Pass();
34 }
35
~NetworkTimeNotifier()36 NetworkTimeNotifier::~NetworkTimeNotifier() {}
37
UpdateNetworkTime(const base::Time & network_time,const base::TimeDelta & resolution,const base::TimeDelta & latency,const base::TimeTicks & post_time)38 void NetworkTimeNotifier::UpdateNetworkTime(const base::Time& network_time,
39 const base::TimeDelta& resolution,
40 const base::TimeDelta& latency,
41 const base::TimeTicks& post_time) {
42 DCHECK(thread_checker_.CalledOnValidThread());
43 DVLOG(1) << "Network time updating to "
44 << UTF16ToUTF8(base::TimeFormatFriendlyDateAndTime(network_time));
45 // Update network time on every request to limit dependency on ticks lag.
46 // TODO(mad): Find a heuristic to avoid augmenting the
47 // network_time_uncertainty_ too much by a particularly long latency.
48 // Maybe only update when the the new time either improves in accuracy or
49 // drifts too far from |network_time_|.
50 network_time_ = network_time;
51
52 // Calculate the delay since the network time was received.
53 base::TimeTicks now = tick_clock_->NowTicks();
54 base::TimeDelta task_delay = now - post_time;
55 // Estimate that the time was set midway through the latency time.
56 network_time_ticks_ = now - task_delay - latency / 2;
57
58 // Can't assume a better time than the resolution of the given time
59 // and 5 ticks measurements are involved, each with their own uncertainty.
60 // 1 & 2 are the ones used to compute the latency, 3 is the Now() from when
61 // this task was posted, 4 is the Now() above and 5 will be the Now() used in
62 // GetNetworkTime().
63 network_time_uncertainty_ =
64 resolution + latency + kNumTimeMeasurements *
65 base::TimeDelta::FromMilliseconds(kTicksResolutionMs);
66
67 for (size_t i = 0; i < observers_.size(); ++i) {
68 base::MessageLoop::current()->PostTask(
69 FROM_HERE,
70 base::Bind(observers_[i],
71 network_time_,
72 network_time_ticks_,
73 network_time_uncertainty_));
74 }
75 }
76
AddObserver(const ObserverCallback & observer_callback)77 void NetworkTimeNotifier::AddObserver(
78 const ObserverCallback& observer_callback) {
79 DCHECK(thread_checker_.CalledOnValidThread());
80 observers_.push_back(observer_callback);
81 if (!network_time_.is_null()) {
82 base::MessageLoop::current()->PostTask(
83 FROM_HERE,
84 base::Bind(observer_callback,
85 network_time_,
86 network_time_ticks_,
87 network_time_uncertainty_));
88 }
89 }
90
91 } // namespace net
92