time_point.h

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// Copyright 2013 The Flutter 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 FLUTTER_FML_TIME_TIME_POINT_H_
#define FLUTTER_FML_TIME_TIME_POINT_H_
 
#include <cstdint>
#include <functional>
#include <iosfwd>
 
#include "flutter/fml/time/time_delta.h"
 
namespace fml {
 
// A TimePoint represents a point in time represented as an integer number of
// nanoseconds elapsed since an arbitrary point in the past.
//
// WARNING: This class should not be serialized across reboots, or across
// devices: the reference point is only stable for a given device between
// reboots.
class TimePoint {
 public:
  using ClockSource = TimePoint (*)();
 
  // Default TimePoint with internal value 0 (epoch).
  constexpr TimePoint() = default;
 
  static void SetClockSource(ClockSource source);
 
  static TimePoint Now();
 
  static TimePoint CurrentWallTime();
 
  static constexpr TimePoint Min() {
    return TimePoint(std::numeric_limits<int64_t>::min());
  }
 
  static constexpr TimePoint Max() {
    return TimePoint(std::numeric_limits<int64_t>::max());
  }
 
  static constexpr TimePoint FromEpochDelta(TimeDelta ticks) {
    return TimePoint(ticks.ToNanoseconds());
  }
 
  // Expects ticks in nanos.
  static constexpr TimePoint FromTicks(int64_t ticks) {
    return TimePoint(ticks);
  }
 
  constexpr TimeDelta ToEpochDelta() const {
    return TimeDelta::FromNanoseconds(ticks_);
  }
 
  // Compute the difference between two time points.
  constexpr TimeDelta operator-(TimePoint other) const {
    return TimeDelta::FromNanoseconds(ticks_ - other.ticks_);
  }
 
  constexpr TimePoint operator+(TimeDelta duration) const {
    return TimePoint(ticks_ + duration.ToNanoseconds());
  }
  constexpr TimePoint operator-(TimeDelta duration) const {
    return TimePoint(ticks_ - duration.ToNanoseconds());
  }
 
  constexpr auto operator<=>(const TimePoint& other) const = default;
 
 private:
  explicit constexpr TimePoint(int64_t ticks) : ticks_(ticks) {}
 
  int64_t ticks_ = 0;
};
 
}  // namespace fml
 
#endif  // FLUTTER_FML_TIME_TIME_POINT_H_