base/time.h

// Copyright (c) 2011 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.

// Time represents an absolute point in time, internally represented as
// microseconds (s/1,000,000) since a platform-dependent epoch.  Each
// platform's epoch, along with other system-dependent clock interface
// routines, is defined in time_PLATFORM.cc.
//
// TimeDelta represents a duration of time, internally represented in
// microseconds.
//
// TimeTicks represents an abstract time that is always incrementing for use
// in measuring time durations. It is internally represented in microseconds.
// It can not be converted to a human-readable time, but is guaranteed not to
// decrease (if the user changes the computer clock, Time::Now() may actually
// decrease or jump).
//
// These classes are represented as only a 64-bit value, so they can be
// efficiently passed by value.

#ifndef BASE_TIME_H_
#define BASE_TIME_H_
#pragma once

#include <time.h>

#include "base/atomicops.h"
#include "base/base_export.h"
#include "base/basictypes.h"

#if defined(OS_POSIX)
// For struct timeval.
#include <sys/time.h>
#endif

#if defined(OS_WIN)
// For FILETIME in FromFileTime, until it moves to a new converter class.
// See TODO(iyengar) below.
#include <windows.h>
#endif

namespace base {

class Time;
class TimeTicks;

// TimeDelta ------------------------------------------------------------------

class BASE_EXPORT TimeDelta {
 public:
  TimeDelta() : delta_(0) {
  }

  // Converts units of time to TimeDeltas.
  static TimeDelta FromDays(int64 days);
  static TimeDelta FromHours(int64 hours);
  static TimeDelta FromMinutes(int64 minutes);
  static TimeDelta FromSeconds(int64 secs);
  static TimeDelta FromMilliseconds(int64 ms);
  static TimeDelta FromMicroseconds(int64 us);

  // Converts an integer value representing TimeDelta to a class. This is used
  // when deserializing a |TimeDelta| structure, using a value known to be
  // compatible. It is not provided as a constructor because the integer type
  // may be unclear from the perspective of a caller.
  static TimeDelta FromInternalValue(int64 delta) {
    return TimeDelta(delta);
  }

  // Returns the internal numeric value of the TimeDelta object. Please don't
  // use this and do arithmetic on it, as it is more error prone than using the
  // provided operators.
  // For serializing, use FromInternalValue to reconstitute.
  int64 ToInternalValue() const {
    return delta_;
  }

#if defined(OS_POSIX)
  struct timespec ToTimeSpec() const;
#endif

  // Returns the time delta in some unit. The F versions return a floating
  // point value, the "regular" versions return a rounded-down value.
  //
  // InMillisecondsRoundedUp() instead returns an integer that is rounded up
  // to the next full millisecond.
  int InDays() const;
  int InHours() const;
  int InMinutes() const;
  double InSecondsF() const;
  int64 InSeconds() const;
  double InMillisecondsF() const;
  int64 InMilliseconds() const;
  int64 InMillisecondsRoundedUp() const;
  int64 InMicroseconds() const;

  TimeDelta& operator=(TimeDelta other) {
    delta_ = other.delta_;
    return *this;
  }

  // Computations with other deltas.
  TimeDelta operator+(TimeDelta other) const {
    return TimeDelta(delta_ + other.delta_);
  }
  TimeDelta operator-(TimeDelta other) const {
    return TimeDelta(delta_ - other.delta_);
  }

  TimeDelta& operator+=(TimeDelta other) {
    delta_ += other.delta_;
    return *this;
  }
  TimeDelta& operator-=(TimeDelta other) {
    delta_ -= other.delta_;
    return *this;
  }
  TimeDelta operator-() const {
    return TimeDelta(-delta_);
  }

  // Computations with ints, note that we only allow multiplicative operations
  // with ints, and additive operations with other deltas.
  TimeDelta operator*(int64 a) const {
    return TimeDelta(delta_ * a);
  }
  TimeDelta operator/(int64 a) const {
    return TimeDelta(delta_ / a);
  }
  TimeDelta& operator*=(int64 a) {
    delta_ *= a;
    return *this;
  }
  TimeDelta& operator/=(int64 a) {
    delta_ /= a;
    return *this;
  }
  int64 operator/(TimeDelta a) const {
    return delta_ / a.delta_;
  }

  // Defined below because it depends on the definition of the other classes.
  Time operator+(Time t) const;
  TimeTicks operator+(TimeTicks t) const;

  // Comparison operators.
  bool operator==(TimeDelta other) const {
    return delta_ == other.delta_;
  }
  bool operator!=(TimeDelta other) const {
    return delta_ != other.delta_;
  }
  bool operator<(TimeDelta other) const {
    return delta_ < other.delta_;
  }
  bool operator<=(TimeDelta other) const {
    return delta_ <= other.delta_;
  }
  bool operator>(TimeDelta other) const {
    return delta_ > other.delta_;
  }
  bool operator>=(TimeDelta other) const {
    return delta_ >= other.delta_;
  }

 private:
  friend class Time;
  friend class TimeTicks;
  friend TimeDelta operator*(int64 a, TimeDelta td);

  // Constructs a delta given the duration in microseconds. This is private
  // to avoid confusion by callers with an integer constructor. Use
  // FromSeconds, FromMilliseconds, etc. instead.
  explicit TimeDelta(int64 delta_us) : delta_(delta_us) {
  }

  // Delta in microseconds.
  int64 delta_;
};

inline TimeDelta operator*(int64 a, TimeDelta td) {
  return TimeDelta(a * td.delta_);
}

// Time -----------------------------------------------------------------------

// Represents a wall clock time.
class BASE_EXPORT Time {
 public:
  static const int64 kMillisecondsPerSecond = 1000;
  static const int64 kMicrosecondsPerMillisecond = 1000;
  static const int64 kMicrosecondsPerSecond = kMicrosecondsPerMillisecond *
                                              kMillisecondsPerSecond;
  static const int64 kMicrosecondsPerMinute = kMicrosecondsPerSecond * 60;
  static const int64 kMicrosecondsPerHour = kMicrosecondsPerMinute * 60;
  static const int64 kMicrosecondsPerDay = kMicrosecondsPerHour * 24;
  static const int64 kMicrosecondsPerWeek = kMicrosecondsPerDay * 7;
  static const int64 kNanosecondsPerMicrosecond = 1000;
  static const int64 kNanosecondsPerSecond = kNanosecondsPerMicrosecond *
                                             kMicrosecondsPerSecond;

#if !defined(OS_WIN)
  // On Mac & Linux, this value is the delta from the Windows epoch of 1601 to
  // the Posix delta of 1970. This is used for migrating between the old
  // 1970-based epochs to the new 1601-based ones. It should be removed from
  // this global header and put in the platform-specific ones when we remove the
  // migration code.
  static const int64 kWindowsEpochDeltaMicroseconds;
#endif

  // Represents an exploded time that can be formatted nicely. This is kind of
  // like the Win32 SYSTEMTIME structure or the Unix "struct tm" with a few
  // additions and changes to prevent errors.
  struct BASE_EXPORT Exploded {
    int year;          // Four digit year "2007"
    int month;         // 1-based month (values 1 = January, etc.)
    int day_of_week;   // 0-based day of week (0 = Sunday, etc.)
    int day_of_month;  // 1-based day of month (1-31)
    int hour;          // Hour within the current day (0-23)
    int minute;        // Minute within the current hour (0-59)
    int second;        // Second within the current minute (0-59 plus leap
                       //   seconds which may take it up to 60).
    int millisecond;   // Milliseconds within the current second (0-999)

    // A cursory test for whether the data members are within their
    // respective ranges. A 'true' return value does not guarantee the
    // Exploded value can be successfully converted to a Time value.
    bool HasValidValues() const;
  };

  // Contains the NULL time. Use Time::Now() to get the current time.
  explicit Time() : us_(0) {
  }

  // Returns true if the time object has not been initialized.
  bool is_null() const {
    return us_ == 0;
  }

  // Returns the time for epoch in Unix-like system (Jan 1, 1970).
  static Time UnixEpoch();

  // Returns the current time. Watch out, the system might adjust its clock
  // in which case time will actually go backwards. We don't guarantee that
  // times are increasing, or that two calls to Now() won't be the same.
  static Time Now();

  // Returns the current time. Same as Now() except that this function always
  // uses system time so that there are no discrepancies between the returned
  // time and system time even on virtual environments including our test bot.
  // For timing sensitive unittests, this function should be used.
  static Time NowFromSystemTime();

  // Converts to/from time_t in UTC and a Time class.
  // TODO(brettw) this should be removed once everybody starts using the |Time|
  // class.
  static Time FromTimeT(time_t tt);
  time_t ToTimeT() const;

  // Converts time to/from a double which is the number of seconds since epoch
  // (Jan 1, 1970).  Webkit uses this format to represent time.
  // Because WebKit initializes double time value to 0 to indicate "not
  // initialized", we map it to empty Time object that also means "not
  // initialized".
  static Time FromDoubleT(double dt);
  double ToDoubleT() const;

#if defined(OS_POSIX)
  struct timeval ToTimeVal() const;
#endif

#if defined(OS_WIN)
  static Time FromFileTime(FILETIME ft);
  FILETIME ToFileTime() const;

  // The minimum time of a low resolution timer.  This is basically a windows
  // constant of ~15.6ms.  While it does vary on some older OS versions, we'll
  // treat it as static across all windows versions.
  static const int kMinLowResolutionThresholdMs = 16;

  // Enable or disable Windows high resolution timer. If the high resolution
  // timer is not enabled, calls to ActivateHighResolutionTimer will fail.
  // When disabling the high resolution timer, this function will not cause
  // the high resolution timer to be deactivated, but will prevent future
  // activations.
  // Must be called from the main thread.
  // For more details see comments in time_win.cc.
  static void EnableHighResolutionTimer(bool enable);

  // Activates or deactivates the high resolution timer based on the |activate|
  // flag.  If the HighResolutionTimer is not Enabled (see
  // EnableHighResolutionTimer), this function will return false.  Otherwise
  // returns true.  Each successful activate call must be paired with a
  // subsequent deactivate call.
  // All callers to activate the high resolution timer must eventually call
  // this function to deactivate the high resolution timer.
  static bool ActivateHighResolutionTimer(bool activate);

  // Returns true if the high resolution timer is both enabled and activated.
  // This is provided for testing only, and is not tracked in a thread-safe
  // way.
  static bool IsHighResolutionTimerInUse();
#endif

  // Converts an exploded structure representing either the local time or UTC
  // into a Time class.
  static Time FromUTCExploded(const Exploded& exploded) {
    return FromExploded(false, exploded);
  }
  static Time FromLocalExploded(const Exploded& exploded) {
    return FromExploded(true, exploded);
  }

  // Converts an integer value representing Time to a class. This is used
  // when deserializing a |Time| structure, using a value known to be
  // compatible. It is not provided as a constructor because the integer type
  // may be unclear from the perspective of a caller.
  static Time FromInternalValue(int64 us) {
    return Time(us);
  }

  // Converts a string representation of time to a Time object.
  // An example of a time string which is converted is as below:-
  // "Tue, 15 Nov 1994 12:45:26 GMT". If the timezone is not specified
  // in the input string, we assume local time.
  // TODO(iyengar) Move the FromString/FromTimeT/ToTimeT/FromFileTime to
  // a new time converter class.
  static bool FromString(const char* time_string, Time* parsed_time);

  // For serializing, use FromInternalValue to reconstitute. Please don't use
  // this and do arithmetic on it, as it is more error prone than using the
  // provided operators.
  int64 ToInternalValue() const {
    return us_;
  }

  // Fills the given exploded structure with either the local time or UTC from
  // this time structure (containing UTC).
  void UTCExplode(Exploded* exploded) const {
    return Explode(false, exploded);
  }
  void LocalExplode(Exploded* exploded) const {
    return Explode(true, exploded);
  }

  // Rounds this time down to the nearest day in local time. It will represent
  // midnight on that day.
  Time LocalMidnight() const;

  Time& operator=(Time other) {
    us_ = other.us_;
    return *this;
  }

  // Compute the difference between two times.
  TimeDelta operator-(Time other) const {
    return TimeDelta(us_ - other.us_);
  }

  // Modify by some time delta.
  Time& operator+=(TimeDelta delta) {
    us_ += delta.delta_;
    return *this;
  }
  Time& operator-=(TimeDelta delta) {
    us_ -= delta.delta_;
    return *this;
  }

  // Return a new time modified by some delta.
  Time operator+(TimeDelta delta) const {
    return Time(us_ + delta.delta_);
  }
  Time operator-(TimeDelta delta) const {
    return Time(us_ - delta.delta_);
  }

  // Comparison operators
  bool operator==(Time other) const {
    return us_ == other.us_;
  }
  bool operator!=(Time other) const {
    return us_ != other.us_;
  }
  bool operator<(Time other) const {
    return us_ < other.us_;
  }
  bool operator<=(Time other) const {
    return us_ <= other.us_;
  }
  bool operator>(Time other) const {
    return us_ > other.us_;
  }
  bool operator>=(Time other) const {
    return us_ >= other.us_;
  }

 private:
  friend class TimeDelta;

  explicit Time(int64 us) : us_(us) {
  }

  // Explodes the given time to either local time |is_local = true| or UTC
  // |is_local = false|.
  void Explode(bool is_local, Exploded* exploded) const;

  // Unexplodes a given time assuming the source is either local time
  // |is_local = true| or UTC |is_local = false|.
  static Time FromExploded(bool is_local, const Exploded& exploded);

  // The representation of Jan 1, 1970 UTC in microseconds since the
  // platform-dependent epoch.
  static const int64 kTimeTToMicrosecondsOffset;

#if defined(OS_WIN)
  // Indicates whether fast timers are usable right now.  For instance,
  // when using battery power, we might elect to prevent high speed timers
  // which would draw more power.
  static bool high_resolution_timer_enabled_;
  // Count of activations on the high resolution timer.  Only use in tests
  // which are single threaded.
  static int high_resolution_timer_activated_;
#endif

  // Time in microseconds in UTC.
  int64 us_;
};

// Inline the TimeDelta factory methods, for fast TimeDelta construction.

// static
inline TimeDelta TimeDelta::FromDays(int64 days) {
  return TimeDelta(days * Time::kMicrosecondsPerDay);
}

// static
inline TimeDelta TimeDelta::FromHours(int64 hours) {
  return TimeDelta(hours * Time::kMicrosecondsPerHour);
}

// static
inline TimeDelta TimeDelta::FromMinutes(int64 minutes) {
  return TimeDelta(minutes * Time::kMicrosecondsPerMinute);
}

// static
inline TimeDelta TimeDelta::FromSeconds(int64 secs) {
  return TimeDelta(secs * Time::kMicrosecondsPerSecond);
}

// static
inline TimeDelta TimeDelta::FromMilliseconds(int64 ms) {
  return TimeDelta(ms * Time::kMicrosecondsPerMillisecond);
}

// static
inline TimeDelta TimeDelta::FromMicroseconds(int64 us) {
  return TimeDelta(us);
}

inline Time TimeDelta::operator+(Time t) const {
  return Time(t.us_ + delta_);
}

// TimeTicks ------------------------------------------------------------------

class BASE_EXPORT TimeTicks {
 public:
  TimeTicks() : ticks_(0) {
  }

  // Platform-dependent tick count representing "right now."
  // The resolution of this clock is ~1-15ms.  Resolution varies depending
  // on hardware/operating system configuration.
  static TimeTicks Now();

  // Returns a platform-dependent high-resolution tick count. Implementation
  // is hardware dependent and may or may not return sub-millisecond
  // resolution.  THIS CALL IS GENERALLY MUCH MORE EXPENSIVE THAN Now() AND
  // SHOULD ONLY BE USED WHEN IT IS REALLY NEEDED.
  static TimeTicks HighResNow();

#if defined(OS_WIN)
  // Get the absolute value of QPC time drift. For testing.
  static int64 GetQPCDriftMicroseconds();

  // Returns true if the high resolution clock is working on this system.
  // This is only for testing.
  static bool IsHighResClockWorking();
#endif

  // Returns true if this object has not been initialized.
  bool is_null() const {
    return ticks_ == 0;
  }

  // Converts an integer value representing TimeTicks to a class. This is used
  // when deserializing a |TimeTicks| structure, using a value known to be
  // compatible. It is not provided as a constructor because the integer type
  // may be unclear from the perspective of a caller.
  static TimeTicks FromInternalValue(int64 ticks) {
    return TimeTicks(ticks);
  }

  // Returns the internal numeric value of the TimeTicks object.
  // For serializing, use FromInternalValue to reconstitute.
  int64 ToInternalValue() const {
    return ticks_;
  }

  TimeTicks& operator=(TimeTicks other) {
    ticks_ = other.ticks_;
    return *this;
  }

  // Compute the difference between two times.
  TimeDelta operator-(TimeTicks other) const {
    return TimeDelta(ticks_ - other.ticks_);
  }

  // Modify by some time delta.
  TimeTicks& operator+=(TimeDelta delta) {
    ticks_ += delta.delta_;
    return *this;
  }
  TimeTicks& operator-=(TimeDelta delta) {
    ticks_ -= delta.delta_;
    return *this;
  }

  // Return a new TimeTicks modified by some delta.
  TimeTicks operator+(TimeDelta delta) const {
    return TimeTicks(ticks_ + delta.delta_);
  }
  TimeTicks operator-(TimeDelta delta) const {
    return TimeTicks(ticks_ - delta.delta_);
  }

  // Comparison operators
  bool operator==(TimeTicks other) const {
    return ticks_ == other.ticks_;
  }
  bool operator!=(TimeTicks other) const {
    return ticks_ != other.ticks_;
  }
  bool operator<(TimeTicks other) const {
    return ticks_ < other.ticks_;
  }
  bool operator<=(TimeTicks other) const {
    return ticks_ <= other.ticks_;
  }
  bool operator>(TimeTicks other) const {
    return ticks_ > other.ticks_;
  }
  bool operator>=(TimeTicks other) const {
    return ticks_ >= other.ticks_;
  }

 protected:
  friend class TimeDelta;

  // Please use Now() to create a new object. This is for internal use
  // and testing. Ticks is in microseconds.
  explicit TimeTicks(int64 ticks) : ticks_(ticks) {
  }

  // Tick count in microseconds.
  int64 ticks_;

#if defined(OS_WIN)
  typedef DWORD (*TickFunctionType)(void);
  static TickFunctionType SetMockTickFunction(TickFunctionType ticker);
#endif
};

inline TimeTicks TimeDelta::operator+(TimeTicks t) const {
  return TimeTicks(t.ticks_ + delta_);
}

}  // namespace base

#endif  // BASE_TIME_H_