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// Copyright (c) 2012 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 coordinated universal time (UTC),
// internally represented as microseconds (s/1,000,000) since the Windows epoch
// (1601-01-01 00:00:00 UTC). System-dependent clock interface routines are
// defined in Note that values for Time may skew and jump
// around as the operating system makes adjustments to synchronize (e.g., with
// NTP servers). Thus, client code that uses the Time class must account for
// this.
// TimeDelta represents a duration of time, internally represented in
// microseconds.
// TimeTicks and ThreadTicks represent an abstract time that is most of the time
// incrementing, for use in measuring time durations. Internally, they are
// represented in microseconds. They can not be converted to a human-readable
// time, but are guaranteed not to decrease (unlike the Time class). Note that
// TimeTicks may "stand still" (e.g., if the computer is suspended), and
// ThreadTicks will "stand still" whenever the thread has been de-scheduled by
// the operating system.
// All time classes are copyable, assignable, and occupy 64-bits per
// instance. Thus, they can be efficiently passed by-value (as opposed to
// by-reference).
// Definitions of operator<< are provided to make these types work with
// DCHECK_EQ() and other log macros. For human-readable formatting, see
// "base/i18n/time_formatting.h".
// So many choices! Which time class should you use? Examples:
// Time: Interpreting the wall-clock time provided by a remote
// system. Detecting whether cached resources have
// expired. Providing the user with a display of the current date
// and time. Determining the amount of time between events across
// re-boots of the machine.
// TimeTicks: Tracking the amount of time a task runs. Executing delayed
// tasks at the right time. Computing presentation timestamps.
// Synchronizing audio and video using TimeTicks as a common
// reference clock (lip-sync). Measuring network round-trip
// latency.
// ThreadTicks: Benchmarking how long the current thread has been doing actual
// work.
#include <stdint.h>
#include <time.h>
#include <iosfwd>
#include <limits>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/numerics/safe_math.h"
#include "build/build_config.h"
#if defined(OS_MACOSX)
#include <CoreFoundation/CoreFoundation.h>
// Avoid Mac system header macro leak.
#undef TYPE_BOOL
#if defined(OS_POSIX)
#include <unistd.h>
#include <sys/time.h>
#if defined(OS_WIN)
// For FILETIME in FromFileTime, until it moves to a new converter class.
// See TODO(iyengar) below.
#include <windows.h>
#include "base/gtest_prod_util.h"
namespace base {
class TimeDelta;
// The functions in the time_internal namespace are meant to be used only by the
// time classes and functions. Please use the math operators defined in the
// time classes instead.
namespace time_internal {
// Add or subtract |value| from a TimeDelta. The int64_t argument and return
// value are in terms of a microsecond timebase.
BASE_EXPORT int64_t SaturatedAdd(TimeDelta delta, int64_t value);
BASE_EXPORT int64_t SaturatedSub(TimeDelta delta, int64_t value);
// Clamp |value| on overflow and underflow conditions. The int64_t argument and
// return value are in terms of a microsecond timebase.
BASE_EXPORT int64_t FromCheckedNumeric(const CheckedNumeric<int64_t> value);
} // namespace time_internal
// TimeDelta ------------------------------------------------------------------
class BASE_EXPORT TimeDelta {
TimeDelta() : delta_(0) {
// Converts units of time to TimeDeltas.
static TimeDelta FromDays(int days);
static TimeDelta FromHours(int hours);
static TimeDelta FromMinutes(int minutes);
static TimeDelta FromSeconds(int64_t secs);
static TimeDelta FromMilliseconds(int64_t ms);
static TimeDelta FromSecondsD(double secs);
static TimeDelta FromMillisecondsD(double ms);
static TimeDelta FromMicroseconds(int64_t us);
#if defined(OS_WIN)
static TimeDelta FromQPCValue(LONGLONG qpc_value);
// 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_t delta) { return TimeDelta(delta); }
// Returns the maximum time delta, which should be greater than any reasonable
// time delta we might compare it to. Adding or subtracting the maximum time
// delta to a time or another time delta has an undefined result.
static TimeDelta Max();
// 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_t ToInternalValue() const { return delta_; }
// Returns the magnitude (absolute value) of this TimeDelta.
TimeDelta magnitude() const {
// Some toolchains provide an incomplete C++11 implementation and lack an
// int64_t overload for std::abs(). The following is a simple branchless
// implementation:
const int64_t mask = delta_ >> (sizeof(delta_) * 8 - 1);
return TimeDelta((delta_ + mask) ^ mask);
// Returns true if the time delta is zero.
bool is_zero() const {
return delta_ == 0;
// Returns true if the time delta is the maximum time delta.
bool is_max() const { return delta_ == std::numeric_limits<int64_t>::max(); }
#if defined(OS_POSIX)
struct timespec ToTimeSpec() const;
// 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_t InSeconds() const;
double InMillisecondsF() const;
int64_t InMilliseconds() const;
int64_t InMillisecondsRoundedUp() const;
int64_t InMicroseconds() const;
TimeDelta& operator=(TimeDelta other) {
delta_ = other.delta_;
return *this;
// Computations with other deltas.
TimeDelta operator+(TimeDelta other) const {
return TimeDelta(time_internal::SaturatedAdd(*this, other.delta_));
TimeDelta operator-(TimeDelta other) const {
return TimeDelta(time_internal::SaturatedSub(*this, other.delta_));
TimeDelta& operator+=(TimeDelta other) {
return *this = (*this + other);
TimeDelta& operator-=(TimeDelta other) {
return *this = (*this - other);
TimeDelta operator-() const {
return TimeDelta(-delta_);
// Computations with numeric types.
template<typename T>
TimeDelta operator*(T a) const {
CheckedNumeric<int64_t> rv(delta_);
rv *= a;
return TimeDelta(time_internal::FromCheckedNumeric(rv));
template<typename T>
TimeDelta operator/(T a) const {
CheckedNumeric<int64_t> rv(delta_);
rv /= a;
return TimeDelta(time_internal::FromCheckedNumeric(rv));
template<typename T>
TimeDelta& operator*=(T a) {
return *this = (*this * a);
template<typename T>
TimeDelta& operator/=(T a) {
return *this = (*this / a);
int64_t operator/(TimeDelta a) const { return delta_ / a.delta_; }
TimeDelta operator%(TimeDelta a) const {
return TimeDelta(delta_ % a.delta_);
// 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_;
friend int64_t time_internal::SaturatedAdd(TimeDelta delta, int64_t value);
friend int64_t time_internal::SaturatedSub(TimeDelta delta, int64_t value);
// 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_t delta_us) : delta_(delta_us) {}
// Private method to build a delta from a double.
static TimeDelta FromDouble(double value);
// Delta in microseconds.
int64_t delta_;
template<typename T>
inline TimeDelta operator*(T a, TimeDelta td) {
return td * a;
// For logging use only.
BASE_EXPORT std::ostream& operator<<(std::ostream& os, TimeDelta time_delta);
// Do not reference the time_internal::TimeBase template class directly. Please
// use one of the time subclasses instead, and only reference the public
// TimeBase members via those classes.
namespace time_internal {
// TimeBase--------------------------------------------------------------------
// Provides value storage and comparison/math operations common to all time
// classes. Each subclass provides for strong type-checking to ensure
// semantically meaningful comparison/math of time values from the same clock
// source or timeline.
template<class TimeClass>
class TimeBase {
static const int64_t kHoursPerDay = 24;
static const int64_t kMillisecondsPerSecond = 1000;
static const int64_t kMillisecondsPerDay =
kMillisecondsPerSecond * 60 * 60 * kHoursPerDay;
static const int64_t kMicrosecondsPerMillisecond = 1000;
static const int64_t kMicrosecondsPerSecond =
kMicrosecondsPerMillisecond * kMillisecondsPerSecond;
static const int64_t kMicrosecondsPerMinute = kMicrosecondsPerSecond * 60;
static const int64_t kMicrosecondsPerHour = kMicrosecondsPerMinute * 60;
static const int64_t kMicrosecondsPerDay =
kMicrosecondsPerHour * kHoursPerDay;
static const int64_t kMicrosecondsPerWeek = kMicrosecondsPerDay * 7;
static const int64_t kNanosecondsPerMicrosecond = 1000;
static const int64_t kNanosecondsPerSecond =
kNanosecondsPerMicrosecond * kMicrosecondsPerSecond;
// Returns true if this object has not been initialized.
// Warning: Be careful when writing code that performs math on time values,
// since it's possible to produce a valid "zero" result that should not be
// interpreted as a "null" value.
bool is_null() const {
return us_ == 0;
// Returns true if this object represents the maximum time.
bool is_max() const { return us_ == std::numeric_limits<int64_t>::max(); }
// Returns the maximum time, which should be greater than any reasonable time
// with which we might compare it.
static TimeClass Max() {
return TimeClass(std::numeric_limits<int64_t>::max());
// For serializing only. 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_t ToInternalValue() const { return us_; }
TimeClass& operator=(TimeClass other) {
us_ = other.us_;
return *(static_cast<TimeClass*>(this));
// Compute the difference between two times.
TimeDelta operator-(TimeClass other) const {
return TimeDelta::FromMicroseconds(us_ - other.us_);
// Return a new time modified by some delta.
TimeClass operator+(TimeDelta delta) const {
return TimeClass(time_internal::SaturatedAdd(delta, us_));
TimeClass operator-(TimeDelta delta) const {
return TimeClass(-time_internal::SaturatedSub(delta, us_));
// Modify by some time delta.
TimeClass& operator+=(TimeDelta delta) {
return static_cast<TimeClass&>(*this = (*this + delta));
TimeClass& operator-=(TimeDelta delta) {
return static_cast<TimeClass&>(*this = (*this - delta));
// Comparison operators
bool operator==(TimeClass other) const {
return us_ == other.us_;
bool operator!=(TimeClass other) const {
return us_ != other.us_;
bool operator<(TimeClass other) const {
return us_ < other.us_;
bool operator<=(TimeClass other) const {
return us_ <= other.us_;
bool operator>(TimeClass other) const {
return us_ > other.us_;
bool operator>=(TimeClass other) const {
return us_ >= other.us_;
// Converts an integer value representing TimeClass to a class. This is used
// when deserializing a |TimeClass| 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 TimeClass FromInternalValue(int64_t us) { return TimeClass(us); }
explicit TimeBase(int64_t us) : us_(us) {}
// Time value in a microsecond timebase.
int64_t us_;
} // namespace time_internal
template<class TimeClass>
inline TimeClass operator+(TimeDelta delta, TimeClass t) {
return t + delta;
// Time -----------------------------------------------------------------------
// Represents a wall clock time in UTC. Values are not guaranteed to be
// monotonically non-decreasing and are subject to large amounts of skew.
class BASE_EXPORT Time : public time_internal::TimeBase<Time> {
// The representation of Jan 1, 1970 UTC in microseconds since the
// platform-dependent epoch.
static const int64_t kTimeTToMicrosecondsOffset;
#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_t kWindowsEpochDeltaMicroseconds;
// To avoid overflow in QPC to Microseconds calculations, since we multiply
// by kMicrosecondsPerSecond, then the QPC value should not exceed
// (2^63 - 1) / 1E6. If it exceeds that threshold, we divide then multiply.
enum : int64_t{kQPCOverflowThreshold = 0x8637BD05AF7};
// 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 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.
Time() : TimeBase(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)
// Converts the timespec structure to time. MacOS X 10.8.3 (and tentatively,
// earlier versions) will have the |ts|'s tv_nsec component zeroed out,
// having a 1 second resolution, which agrees with
static Time FromTimeSpec(const timespec& ts);
// Converts to/from the Javascript convention for times, a number of
// milliseconds since the epoch:
static Time FromJsTime(double ms_since_epoch);
double ToJsTime() const;
// Converts to Java convention for times, a number of
// milliseconds since the epoch.
int64_t ToJavaTime() const;
#if defined(OS_POSIX)
static Time FromTimeVal(struct timeval t);
struct timeval ToTimeVal() const;
#if defined(OS_MACOSX)
static Time FromCFAbsoluteTime(CFAbsoluteTime t);
CFAbsoluteTime ToCFAbsoluteTime() const;
#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.
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();
// Converts an exploded structure representing either the local time or UTC
// into a Time class.
// TODO(maksims): Get rid of these in favor of the methods below when
// all the callers stop using these ones.
static Time FromUTCExploded(const Exploded& exploded) {
base::Time time;
ignore_result(FromUTCExploded(exploded, &time));
return time;
static Time FromLocalExploded(const Exploded& exploded) {
base::Time time;
ignore_result(FromLocalExploded(exploded, &time));
return time;
// Converts an exploded structure representing either the local time or UTC
// into a Time class. Returns false on a failure when, for example, a day of
// month is set to 31 on a 28-30 day month.
static bool FromUTCExploded(const Exploded& exploded,
return FromExploded(false, exploded, time);
static bool FromLocalExploded(const Exploded& exploded,
return FromExploded(true, exploded, time);
// 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;
friend class time_internal::TimeBase<Time>;
explicit Time(int64_t us) : TimeBase(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|. Function returns false on
// failure and sets |time| to Time(0). Otherwise returns true and sets |time|
// to non-exploded time.
static bool FromExploded(bool is_local,
const Exploded& exploded,
// Comparison does not consider |day_of_week| when doing the operation.
static bool ExplodedMostlyEquals(const Exploded& lhs, const Exploded& rhs);
// Inline the TimeDelta factory methods, for fast TimeDelta construction.
// static
inline TimeDelta TimeDelta::FromDays(int days) {
if (days == std::numeric_limits<int>::max())
return Max();
return TimeDelta(days * Time::kMicrosecondsPerDay);
// static
inline TimeDelta TimeDelta::FromHours(int hours) {
if (hours == std::numeric_limits<int>::max())
return Max();
return TimeDelta(hours * Time::kMicrosecondsPerHour);
// static
inline TimeDelta TimeDelta::FromMinutes(int minutes) {
if (minutes == std::numeric_limits<int>::max())
return Max();
return TimeDelta(minutes * Time::kMicrosecondsPerMinute);
// static
inline TimeDelta TimeDelta::FromSeconds(int64_t secs) {
return TimeDelta(secs) * Time::kMicrosecondsPerSecond;
// static
inline TimeDelta TimeDelta::FromMilliseconds(int64_t ms) {
return TimeDelta(ms) * Time::kMicrosecondsPerMillisecond;
// static
inline TimeDelta TimeDelta::FromSecondsD(double secs) {
return FromDouble(secs * Time::kMicrosecondsPerSecond);
// static
inline TimeDelta TimeDelta::FromMillisecondsD(double ms) {
return FromDouble(ms * Time::kMicrosecondsPerMillisecond);
// static
inline TimeDelta TimeDelta::FromMicroseconds(int64_t us) {
return TimeDelta(us);
// static
inline TimeDelta TimeDelta::FromDouble(double value) {
double max_magnitude = std::numeric_limits<int64_t>::max();
TimeDelta delta = TimeDelta(static_cast<int64_t>(value));
if (value > max_magnitude)
delta = Max();
else if (value < -max_magnitude)
delta = -Max();
return delta;
// For logging use only.
BASE_EXPORT std::ostream& operator<<(std::ostream& os, Time time);
// TimeTicks ------------------------------------------------------------------
// Represents monotonically non-decreasing clock time.
class TimeTicks : public time_internal::TimeBase<TimeTicks> {
TimeTicks() : TimeBase(0) {
// Platform-dependent tick count representing "right now." When
// IsHighResolution() returns false, the resolution of the clock could be
// as coarse as ~15.6ms. Otherwise, the resolution should be no worse than one
// microsecond.
static TimeTicks Now();
// Returns true if the high resolution clock is working on this system and
// Now() will return high resolution values. Note that, on systems where the
// high resolution clock works but is deemed inefficient, the low resolution
// clock will be used instead.
static bool IsHighResolution();
#if defined(OS_WIN)
// Translates an absolute QPC timestamp into a TimeTicks value. The returned
// value has the same origin as Now(). Do NOT attempt to use this if
// IsHighResolution() returns false.
static TimeTicks FromQPCValue(LONGLONG qpc_value);
// Get an estimate of the TimeTick value at the time of the UnixEpoch. Because
// Time and TimeTicks respond differently to user-set time and NTP
// adjustments, this number is only an estimate. Nevertheless, this can be
// useful when you need to relate the value of TimeTicks to a real time and
// date. Note: Upon first invocation, this function takes a snapshot of the
// realtime clock to establish a reference point. This function will return
// the same value for the duration of the application, but will be different
// in future application runs.
static TimeTicks UnixEpoch();
// Returns |this| snapped to the next tick, given a |tick_phase| and
// repeating |tick_interval| in both directions. |this| may be before,
// after, or equal to the |tick_phase|.
TimeTicks SnappedToNextTick(TimeTicks tick_phase,
TimeDelta tick_interval) const;
#if defined(OS_WIN)
typedef DWORD (*TickFunctionType)(void);
static TickFunctionType SetMockTickFunction(TickFunctionType ticker);
friend class time_internal::TimeBase<TimeTicks>;
// Please use Now() to create a new object. This is for internal use
// and testing.
explicit TimeTicks(int64_t us) : TimeBase(us) {}
// For logging use only.
std::ostream& operator<<(std::ostream& os, TimeTicks time_ticks);
// ThreadTicks ----------------------------------------------------------------
// Represents a clock, specific to a particular thread, than runs only while the
// thread is running.
class ThreadTicks : public time_internal::TimeBase<ThreadTicks> {
ThreadTicks() : TimeBase(0) {
// Returns true if ThreadTicks::Now() is supported on this system.
static bool IsSupported() {
#if (defined(_POSIX_THREAD_CPUTIME) && (_POSIX_THREAD_CPUTIME >= 0)) || \
(defined(OS_MACOSX) && !defined(OS_IOS)) || defined(OS_ANDROID)
return true;
#elif defined(OS_WIN)
return IsSupportedWin();
return false;
// Waits until the initialization is completed. Needs to be guarded with a
// call to IsSupported().
static void WaitUntilInitialized() {
#if defined(OS_WIN)
// Returns thread-specific CPU-time on systems that support this feature.
// Needs to be guarded with a call to IsSupported(). Use this timer
// to (approximately) measure how much time the calling thread spent doing
// actual work vs. being de-scheduled. May return bogus results if the thread
// migrates to another CPU between two calls. Returns an empty ThreadTicks
// object until the initialization is completed. If a clock reading is
// absolutely needed, call WaitUntilInitialized() before this method.
static ThreadTicks Now();
friend class time_internal::TimeBase<ThreadTicks>;
// Please use Now() to create a new object. This is for internal use
// and testing.
explicit ThreadTicks(int64_t us) : TimeBase(us) {}
// For logging use only.
std::ostream& operator<<(std::ostream& os, ThreadTicks time_ticks);
} // namespace base
#endif // BASE_TIME_TIME_H_