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// Copyright 2014 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 COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
#define COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "base/threading/thread_checker.h"
#include "base/time/clock.h"
#include "base/time/time.h"
class PrefRegistrySimple;
class PrefService;
namespace base {
class TickClock;
}
namespace network_time {
// Clock resolution is platform dependent.
#if defined(OS_WIN)
const int64_t kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs;
#else
const int64_t kTicksResolutionMs = 1; // Assume 1ms for non-windows platforms.
#endif
// A class that receives network time updates and can provide the network time
// for a corresponding local time. This class is not thread safe.
class NetworkTimeTracker {
public:
static void RegisterPrefs(PrefRegistrySimple* registry);
NetworkTimeTracker(scoped_ptr<base::Clock> clock,
scoped_ptr<base::TickClock> tick_clock,
PrefService* pref_service);
~NetworkTimeTracker();
// Sets |network_time| to an estimate of the true time. Returns true if time
// is available, and false otherwise. If |uncertainty| is non-NULL, it will
// be set to an estimate of the error range.
//
// Network time may be available on startup if deserialized from a pref.
// Failing that, a call to |UpdateNetworkTime| is required to make time
// available to callers of |GetNetworkTime|. Subsequently, network time may
// become unavailable if |NetworkTimeTracker| has reason to believe it is no
// longer accurate. Consumers should even be prepared to handle the case
// where calls to |GetNetworkTime| never once succeeds.
bool GetNetworkTime(base::Time* network_time,
base::TimeDelta* uncertainty) const;
// Calculates corresponding time ticks according to the given parameters.
// 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(base::Time network_time,
base::TimeDelta resolution,
base::TimeDelta latency,
base::TimeTicks post_time);
private:
// The |Clock| and |TickClock| are used to sanity-check one another, allowing
// the NetworkTimeTracker to notice e.g. suspend/resume events and clock
// resets.
scoped_ptr<base::Clock> clock_;
scoped_ptr<base::TickClock> tick_clock_;
PrefService* pref_service_;
// Network time based on last call to UpdateNetworkTime().
mutable base::Time network_time_at_last_measurement_;
// The estimated local times that correspond with |network_time_|. Assumes
// the actual network time measurement was performed midway through the
// latency time. See UpdateNetworkTime(...) implementation for details. The
// tick clock is the one actually used to return values to callers, but both
// clocks must agree to within some tolerance.
base::Time time_at_last_measurement_;
base::TimeTicks ticks_at_last_measurement_;
// Uncertainty of |network_time_| based on added inaccuracies/resolution. See
// UpdateNetworkTime(...) implementation for details.
base::TimeDelta network_time_uncertainty_;
base::ThreadChecker thread_checker_;
bool received_network_time_;
DISALLOW_COPY_AND_ASSIGN(NetworkTimeTracker);
};
} // namespace network_time
#endif // COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
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