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// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef NET_BASE_NETWORK_TIME_NOTIFIER_H_
#define NET_BASE_NETWORK_TIME_NOTIFIER_H_
#include <vector>
#include "base/callback.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/threading/thread_checker.h"
#include "base/time/tick_clock.h"
#include "base/time/time.h"
#include "net/base/net_export.h"
namespace net {
// A class that receives updates for and maintains network time. Network time
// sources can pass updates through UpdateNetworkTime, and network time
// consumers can register as observers. This class is not thread-safe.
class NET_EXPORT NetworkTimeNotifier {
public:
// Callback for observers to receive network time updates.
// The parameters are:
// const base::Time& network_time - the new network time.
// const base::TimeTicks& network_time_ticks - the ticks time that corresponds
// with |network_time|.
// const base::TimeDelta& network_time_uncertainty - the uncertainty
// associated with the new network time.
typedef base::Callback<void(const base::Time&,
const base::TimeTicks&,
const base::TimeDelta&)> ObserverCallback;
// Takes ownership of |tick_clock|.
explicit NetworkTimeNotifier(scoped_ptr<base::TickClock> tick_clock);
~NetworkTimeNotifier();
// Calculates corresponding time ticks according to the given parameters and
// notifies observers. The provided |network_time| is precise at the given
// |resolution| and represent the time between now and up to |latency| +
// (now - |post_time|) ago.
void UpdateNetworkTime(const base::Time& network_time,
const base::TimeDelta& resolution,
const base::TimeDelta& latency,
const base::TimeTicks& post_time);
// |observer_callback| will invoked every time the network time is updated, or
// if a network time is already available when AddObserver is called.
void AddObserver(const ObserverCallback& observer_callback);
private:
base::ThreadChecker thread_checker_;
// For querying current time ticks.
scoped_ptr<base::TickClock> tick_clock_;
// The network time based on last call to UpdateNetworkTime().
base::Time network_time_;
// The estimated local time from |tick_clock| that corresponds with
// |network_time|. Assumes the actual network time measurement was performed
// midway through the latency time, and does not account for suspect/resume
// events since the network time was measured.
// See UpdateNetworkTime(..) implementation for details.
base::TimeTicks network_time_ticks_;
// Uncertainty of |network_time_| based on added inaccuracies/resolution.
// See UpdateNetworkTime(..) implementation for details.
base::TimeDelta network_time_uncertainty_;
// List of network time update observers.
// A vector of callbacks is used, rather than an ObserverList, so that the
// lifetime of the observer can be bound to the callback.
std::vector<ObserverCallback> observers_;
DISALLOW_COPY_AND_ASSIGN(NetworkTimeNotifier);
};
} // namespace net
#endif // NET_BASE_NETWORK_TIME_NOTIFIER_H_
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