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| 1 // Copyright 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 "chrome/browser/network_time/network_time_tracker.h" | |
| 6 | |
| 7 #include "base/basictypes.h" | |
| 8 #include "base/i18n/time_formatting.h" | |
| 9 #include "base/logging.h" | |
| 10 #include "base/prefs/pref_registry_simple.h" | |
| 11 #include "base/prefs/pref_service.h" | |
| 12 #include "base/strings/utf_string_conversions.h" | |
| 13 #include "base/time/tick_clock.h" | |
| 14 #include "chrome/common/pref_names.h" | |
| 15 | |
| 16 namespace { | |
| 17 | |
| 18 // Clock resolution is platform dependent. | |
| 19 #if defined(OS_WIN) | |
| 20 const int64 kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs; | |
| 21 #else | |
| 22 const int64 kTicksResolutionMs = 1; // Assume 1ms for non-windows platforms. | |
| 23 #endif | |
| 24 | |
| 25 // Number of time measurements performed in a given network time calculation. | |
| 26 const int kNumTimeMeasurements = 5; | |
| 27 | |
| 28 } // namespace | |
| 29 | |
| 30 // static | |
| 31 void NetworkTimeTracker::RegisterPrefs(PrefRegistrySimple* registry) { | |
| 32 registry->RegisterDictionaryPref(prefs::kNetworkTimeMapping, | |
| 33 new base::DictionaryValue()); | |
| 34 } | |
| 35 | |
| 36 NetworkTimeTracker::NetworkTimeTracker(scoped_ptr<base::TickClock> tick_clock, | |
| 37 PrefService* pref_service) | |
| 38 : tick_clock_(tick_clock.Pass()), | |
| 39 pref_service_(pref_service), | |
| 40 received_network_time_(false) { | |
| 41 const base::DictionaryValue* time_mapping = | |
| 42 pref_service_->GetDictionary(prefs::kNetworkTimeMapping); | |
| 43 double local_time_js = 0; | |
| 44 double network_time_js = 0; | |
| 45 if (time_mapping->GetDouble("local", &local_time_js) && | |
| 46 time_mapping->GetDouble("network", &network_time_js)) { | |
| 47 base::Time local_time_saved = base::Time::FromJsTime(local_time_js); | |
| 48 base::Time local_time_now = base::Time::Now(); | |
| 49 if (local_time_saved > local_time_now || | |
| 50 local_time_now - local_time_saved > base::TimeDelta::FromDays(7)) { | |
| 51 // Drop saved mapping if clock skew has changed or the data is too old. | |
| 52 pref_service_->ClearPref(prefs::kNetworkTimeMapping); | |
| 53 } else { | |
| 54 network_time_ = base::Time::FromJsTime(network_time_js) + | |
| 55 (local_time_now - local_time_saved); | |
| 56 network_time_ticks_ = base::TimeTicks::Now(); | |
| 57 } | |
| 58 } | |
| 59 } | |
| 60 | |
| 61 NetworkTimeTracker::~NetworkTimeTracker() { | |
| 62 DCHECK(thread_checker_.CalledOnValidThread()); | |
| 63 } | |
| 64 | |
| 65 void NetworkTimeTracker::UpdateNetworkTime(base::Time network_time, | |
| 66 base::TimeDelta resolution, | |
| 67 base::TimeDelta latency, | |
| 68 base::TimeTicks post_time) { | |
| 69 DCHECK(thread_checker_.CalledOnValidThread()); | |
| 70 DVLOG(1) << "Network time updating to " | |
| 71 << base::UTF16ToUTF8( | |
| 72 base::TimeFormatFriendlyDateAndTime(network_time)); | |
| 73 // Update network time on every request to limit dependency on ticks lag. | |
| 74 // TODO(mad): Find a heuristic to avoid augmenting the | |
| 75 // network_time_uncertainty_ too much by a particularly long latency. | |
| 76 // Maybe only update when the the new time either improves in accuracy or | |
| 77 // drifts too far from |network_time_|. | |
| 78 network_time_ = network_time; | |
| 79 | |
| 80 // Calculate the delay since the network time was received. | |
| 81 base::TimeTicks now = tick_clock_->NowTicks(); | |
| 82 base::TimeDelta task_delay = now - post_time; | |
| 83 // Estimate that the time was set midway through the latency time. | |
| 84 network_time_ticks_ = now - task_delay - latency / 2; | |
| 85 | |
| 86 // Can't assume a better time than the resolution of the given time | |
| 87 // and 5 ticks measurements are involved, each with their own uncertainty. | |
| 88 // 1 & 2 are the ones used to compute the latency, 3 is the Now() from when | |
| 89 // this task was posted, 4 is the Now() above and 5 will be the Now() used in | |
| 90 // GetNetworkTime(). | |
| 91 network_time_uncertainty_ = | |
| 92 resolution + latency + kNumTimeMeasurements * | |
| 93 base::TimeDelta::FromMilliseconds(kTicksResolutionMs); | |
| 94 | |
| 95 received_network_time_ = true; | |
| 96 | |
| 97 base::Time network_time_now; | |
| 98 if (GetNetworkTime(base::TimeTicks::Now(), &network_time_now, NULL)) { | |
| 99 // Update time mapping if tracker received time update from server, i.e. | |
| 100 // mapping is accurate. | |
| 101 base::Time local_now = base::Time::Now(); | |
| 102 base::DictionaryValue time_mapping; | |
| 103 time_mapping.SetDouble("local", local_now.ToJsTime()); | |
| 104 time_mapping.SetDouble("network", network_time_now.ToJsTime()); | |
| 105 pref_service_->Set(prefs::kNetworkTimeMapping, time_mapping); | |
| 106 } | |
| 107 } | |
| 108 | |
| 109 bool NetworkTimeTracker::GetNetworkTime(base::TimeTicks time_ticks, | |
| 110 base::Time* network_time, | |
| 111 base::TimeDelta* uncertainty) const { | |
| 112 DCHECK(thread_checker_.CalledOnValidThread()); | |
| 113 DCHECK(network_time); | |
| 114 if (network_time_.is_null()) | |
| 115 return false; | |
| 116 DCHECK(!network_time_ticks_.is_null()); | |
| 117 *network_time = network_time_ + (time_ticks - network_time_ticks_); | |
| 118 if (uncertainty) | |
| 119 *uncertainty = network_time_uncertainty_; | |
| 120 return true; | |
| 121 } | |
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Chromium Code Reviews
Issue 296453005:
Componentize chrome/browser/network_time (Closed)
Base URL: svn://svn.chromium.org/chrome/trunk/src