chromecast/base/system_time_change_notifier.cc

   1 // Copyright 2015 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 "chromecast/base/system_time_change_notifier.h"
   6
   7 #include "base/location.h"
   8 #include "base/sequenced_task_runner.h"
   9
  10 namespace chromecast {
  11
  12 namespace {
  13
  14 // Limits for periodic system time monitoring.
  15 const int kLimitForMonitorPer1Sec = 60;  // 1 minute
  16 const int kLimitForMonitorPer10Sec = 600;  // 10 minutes
  17
  18 }  // namespace
  19
  20 SystemTimeChangeNotifier::SystemTimeChangeNotifier()
  21     : observer_list_(new base::ObserverListThreadSafe<Observer>()) {
  22 }
  23
  24 SystemTimeChangeNotifier::~SystemTimeChangeNotifier() {
  25 }
  26
  27 void SystemTimeChangeNotifier::AddObserver(Observer* observer) {
  28   observer_list_->AddObserver(observer);
  29 }
  30
  31 void SystemTimeChangeNotifier::RemoveObserver(Observer* observer) {
  32   observer_list_->RemoveObserver(observer);
  33 }
  34
  35 void SystemTimeChangeNotifier::NotifySystemTimeChanged() {
  36   observer_list_->Notify(FROM_HERE, &Observer::OnSystemTimeChanged);
  37 }
  38
  39 SystemTimeChangeNotifierPeriodicMonitor::
  40 SystemTimeChangeNotifierPeriodicMonitor(
  41     const scoped_refptr<base::SequencedTaskRunner>& task_runner)
  42     : task_runner_(task_runner),
  43       weak_factory_(this) {
  44   DCHECK(task_runner_);
  45 }
  46
  47 SystemTimeChangeNotifierPeriodicMonitor::
  48 ~SystemTimeChangeNotifierPeriodicMonitor() {
  49 }
  50
  51 void SystemTimeChangeNotifierPeriodicMonitor::Initialize() {
  52   base::Time now = Now();
  53   ResetTimeAndLimits(now);
  54   ScheduleNextMonitor(now);
  55 }
  56
  57 void SystemTimeChangeNotifierPeriodicMonitor::Finalize() {
  58 }
  59
  60 void SystemTimeChangeNotifierPeriodicMonitor::ResetTimeAndLimits(
  61     base::Time now) {
  62   // ScheduleNextMonitor() will adjust actual expected_system_time.
  63   expected_system_time_ = now;
  64   monitoring_limit_time_1sec_ =
  65       now + base::TimeDelta::FromSeconds(kLimitForMonitorPer1Sec);
  66   monitoring_limit_time_10sec_ =
  67       monitoring_limit_time_1sec_ +
  68       base::TimeDelta::FromSeconds(kLimitForMonitorPer10Sec);
  69 }
  70
  71 void SystemTimeChangeNotifierPeriodicMonitor::ScheduleNextMonitor(
  72     base::Time now) {
  73   base::TimeDelta next_checking_interval =
  74       now <= monitoring_limit_time_1sec_ ? base::TimeDelta::FromSeconds(1) :
  75       now <= monitoring_limit_time_10sec_ ? base::TimeDelta::FromSeconds(10) :
  76       base::TimeDelta::FromMinutes(10);
  77   // Adjusting expected_system_time based on now cannot detect continuous system
  78   // time drift (false negative), but tolerates task delay (false positive).
  79   // Task delay is expected more than system time drift.
  80   expected_system_time_ = now + next_checking_interval;
  81   task_runner_->PostDelayedTask(
  82       FROM_HERE,
  83       base::Bind(&SystemTimeChangeNotifierPeriodicMonitor::CheckSystemTime,
  84                  weak_factory_.GetWeakPtr()),
  85       next_checking_interval);
  86 }
  87
  88 void SystemTimeChangeNotifierPeriodicMonitor::CheckSystemTime() {
  89   base::Time now = Now();
  90   const base::TimeDelta kInterval10Seconds(base::TimeDelta::FromSeconds(10));
  91   if (now < expected_system_time_ - kInterval10Seconds ||
  92       now > expected_system_time_ + kInterval10Seconds) {  // Time changed!
  93     ResetTimeAndLimits(now);
  94     NotifySystemTimeChanged();
  95   }
  96   ScheduleNextMonitor(now);
  97 }
  98
  99 base::Time SystemTimeChangeNotifierPeriodicMonitor::Now() const {
 100   if (!fake_now_.is_null())
 101     return fake_now_;
 102   return base::Time::Now();
 103 }
 104
 105 }  // namespace chromecast