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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 // Time represents an absolute point in coordinated universal time (UTC),
6 // internally represented as microseconds (s/1,000,000) since the Windows epoch
7 // (1601-01-01 00:00:00 UTC) (See http://crbug.com/14734).  System-dependent
8 // clock interface routines are defined in time_PLATFORM.cc.
9 //
10 // TimeDelta represents a duration of time, internally represented in
11 // microseconds.
12 //
13 // TimeTicks represents an abstract time that is most of the time incrementing
14 // for use in measuring time durations. It is internally represented in
15 // microseconds.  It can not be converted to a human-readable time, but is
16 // guaranteed not to decrease (if the user changes the computer clock,
17 // Time::Now() may actually decrease or jump).  But note that TimeTicks may
18 // "stand still", for example if the computer suspended.
19 //
20 // These classes are represented as only a 64-bit value, so they can be
21 // efficiently passed by value.
22 
23 #ifndef BASE_TIME_TIME_H_
24 #define BASE_TIME_TIME_H_
25 
26 #include <time.h>
27 
28 #include "base/base_export.h"
29 #include "base/basictypes.h"
30 #include "build/build_config.h"
31 
32 #if defined(OS_MACOSX)
33 #include <CoreFoundation/CoreFoundation.h>
34 // Avoid Mac system header macro leak.
35 #undef TYPE_BOOL
36 #endif
37 
38 #if defined(OS_POSIX)
39 #include <unistd.h>
40 #include <sys/time.h>
41 #endif
42 
43 #if defined(OS_WIN)
44 // For FILETIME in FromFileTime, until it moves to a new converter class.
45 // See TODO(iyengar) below.
46 #include <windows.h>
47 #endif
48 
49 #include <limits>
50 
51 namespace base {
52 
53 class Time;
54 class TimeTicks;
55 
56 // TimeDelta ------------------------------------------------------------------
57 
58 class BASE_EXPORT TimeDelta {
59  public:
TimeDelta()60   TimeDelta() : delta_(0) {
61   }
62 
63   // Converts units of time to TimeDeltas.
64   static TimeDelta FromDays(int days);
65   static TimeDelta FromHours(int hours);
66   static TimeDelta FromMinutes(int minutes);
67   static TimeDelta FromSeconds(int64 secs);
68   static TimeDelta FromMilliseconds(int64 ms);
69   static TimeDelta FromSecondsD(double secs);
70   static TimeDelta FromMillisecondsD(double ms);
71   static TimeDelta FromMicroseconds(int64 us);
72 #if defined(OS_WIN)
73   static TimeDelta FromQPCValue(LONGLONG qpc_value);
74 #endif
75 
76   // Converts an integer value representing TimeDelta to a class. This is used
77   // when deserializing a |TimeDelta| structure, using a value known to be
78   // compatible. It is not provided as a constructor because the integer type
79   // may be unclear from the perspective of a caller.
FromInternalValue(int64 delta)80   static TimeDelta FromInternalValue(int64 delta) {
81     return TimeDelta(delta);
82   }
83 
84   // Returns the maximum time delta, which should be greater than any reasonable
85   // time delta we might compare it to. Adding or subtracting the maximum time
86   // delta to a time or another time delta has an undefined result.
87   static TimeDelta Max();
88 
89   // Returns the internal numeric value of the TimeDelta object. Please don't
90   // use this and do arithmetic on it, as it is more error prone than using the
91   // provided operators.
92   // For serializing, use FromInternalValue to reconstitute.
ToInternalValue()93   int64 ToInternalValue() const {
94     return delta_;
95   }
96 
97   // Returns true if the time delta is the maximum time delta.
is_max()98   bool is_max() const {
99     return delta_ == std::numeric_limits<int64>::max();
100   }
101 
102 #if defined(OS_POSIX)
103   struct timespec ToTimeSpec() const;
104 #endif
105 
106   // Returns the time delta in some unit. The F versions return a floating
107   // point value, the "regular" versions return a rounded-down value.
108   //
109   // InMillisecondsRoundedUp() instead returns an integer that is rounded up
110   // to the next full millisecond.
111   int InDays() const;
112   int InHours() const;
113   int InMinutes() const;
114   double InSecondsF() const;
115   int64 InSeconds() const;
116   double InMillisecondsF() const;
117   int64 InMilliseconds() const;
118   int64 InMillisecondsRoundedUp() const;
119   int64 InMicroseconds() const;
120 
121   TimeDelta& operator=(TimeDelta other) {
122     delta_ = other.delta_;
123     return *this;
124   }
125 
126   // Computations with other deltas.
127   TimeDelta operator+(TimeDelta other) const {
128     return TimeDelta(delta_ + other.delta_);
129   }
130   TimeDelta operator-(TimeDelta other) const {
131     return TimeDelta(delta_ - other.delta_);
132   }
133 
134   TimeDelta& operator+=(TimeDelta other) {
135     delta_ += other.delta_;
136     return *this;
137   }
138   TimeDelta& operator-=(TimeDelta other) {
139     delta_ -= other.delta_;
140     return *this;
141   }
142   TimeDelta operator-() const {
143     return TimeDelta(-delta_);
144   }
145 
146   // Computations with ints, note that we only allow multiplicative operations
147   // with ints, and additive operations with other deltas.
148   TimeDelta operator*(int64 a) const {
149     return TimeDelta(delta_ * a);
150   }
151   TimeDelta operator/(int64 a) const {
152     return TimeDelta(delta_ / a);
153   }
154   TimeDelta& operator*=(int64 a) {
155     delta_ *= a;
156     return *this;
157   }
158   TimeDelta& operator/=(int64 a) {
159     delta_ /= a;
160     return *this;
161   }
162   int64 operator/(TimeDelta a) const {
163     return delta_ / a.delta_;
164   }
165 
166   // Defined below because it depends on the definition of the other classes.
167   Time operator+(Time t) const;
168   TimeTicks operator+(TimeTicks t) const;
169 
170   // Comparison operators.
171   bool operator==(TimeDelta other) const {
172     return delta_ == other.delta_;
173   }
174   bool operator!=(TimeDelta other) const {
175     return delta_ != other.delta_;
176   }
177   bool operator<(TimeDelta other) const {
178     return delta_ < other.delta_;
179   }
180   bool operator<=(TimeDelta other) const {
181     return delta_ <= other.delta_;
182   }
183   bool operator>(TimeDelta other) const {
184     return delta_ > other.delta_;
185   }
186   bool operator>=(TimeDelta other) const {
187     return delta_ >= other.delta_;
188   }
189 
190  private:
191   friend class Time;
192   friend class TimeTicks;
193   friend TimeDelta operator*(int64 a, TimeDelta td);
194 
195   // Constructs a delta given the duration in microseconds. This is private
196   // to avoid confusion by callers with an integer constructor. Use
197   // FromSeconds, FromMilliseconds, etc. instead.
TimeDelta(int64 delta_us)198   explicit TimeDelta(int64 delta_us) : delta_(delta_us) {
199   }
200 
201   // Delta in microseconds.
202   int64 delta_;
203 };
204 
205 inline TimeDelta operator*(int64 a, TimeDelta td) {
206   return TimeDelta(a * td.delta_);
207 }
208 
209 // Time -----------------------------------------------------------------------
210 
211 // Represents a wall clock time in UTC.
212 class BASE_EXPORT Time {
213  public:
214   static const int64 kMillisecondsPerSecond = 1000;
215   static const int64 kMicrosecondsPerMillisecond = 1000;
216   static const int64 kMicrosecondsPerSecond = kMicrosecondsPerMillisecond *
217                                               kMillisecondsPerSecond;
218   static const int64 kMicrosecondsPerMinute = kMicrosecondsPerSecond * 60;
219   static const int64 kMicrosecondsPerHour = kMicrosecondsPerMinute * 60;
220   static const int64 kMicrosecondsPerDay = kMicrosecondsPerHour * 24;
221   static const int64 kMicrosecondsPerWeek = kMicrosecondsPerDay * 7;
222   static const int64 kNanosecondsPerMicrosecond = 1000;
223   static const int64 kNanosecondsPerSecond = kNanosecondsPerMicrosecond *
224                                              kMicrosecondsPerSecond;
225 
226 #if !defined(OS_WIN)
227   // On Mac & Linux, this value is the delta from the Windows epoch of 1601 to
228   // the Posix delta of 1970. This is used for migrating between the old
229   // 1970-based epochs to the new 1601-based ones. It should be removed from
230   // this global header and put in the platform-specific ones when we remove the
231   // migration code.
232   static const int64 kWindowsEpochDeltaMicroseconds;
233 #endif
234 
235   // Represents an exploded time that can be formatted nicely. This is kind of
236   // like the Win32 SYSTEMTIME structure or the Unix "struct tm" with a few
237   // additions and changes to prevent errors.
238   struct BASE_EXPORT Exploded {
239     int year;          // Four digit year "2007"
240     int month;         // 1-based month (values 1 = January, etc.)
241     int day_of_week;   // 0-based day of week (0 = Sunday, etc.)
242     int day_of_month;  // 1-based day of month (1-31)
243     int hour;          // Hour within the current day (0-23)
244     int minute;        // Minute within the current hour (0-59)
245     int second;        // Second within the current minute (0-59 plus leap
246                        //   seconds which may take it up to 60).
247     int millisecond;   // Milliseconds within the current second (0-999)
248 
249     // A cursory test for whether the data members are within their
250     // respective ranges. A 'true' return value does not guarantee the
251     // Exploded value can be successfully converted to a Time value.
252     bool HasValidValues() const;
253   };
254 
255   // Contains the NULL time. Use Time::Now() to get the current time.
Time()256   Time() : us_(0) {
257   }
258 
259   // Returns true if the time object has not been initialized.
is_null()260   bool is_null() const {
261     return us_ == 0;
262   }
263 
264   // Returns true if the time object is the maximum time.
is_max()265   bool is_max() const {
266     return us_ == std::numeric_limits<int64>::max();
267   }
268 
269   // Returns the time for epoch in Unix-like system (Jan 1, 1970).
270   static Time UnixEpoch();
271 
272   // Returns the current time. Watch out, the system might adjust its clock
273   // in which case time will actually go backwards. We don't guarantee that
274   // times are increasing, or that two calls to Now() won't be the same.
275   static Time Now();
276 
277   // Returns the maximum time, which should be greater than any reasonable time
278   // with which we might compare it.
279   static Time Max();
280 
281   // Returns the current time. Same as Now() except that this function always
282   // uses system time so that there are no discrepancies between the returned
283   // time and system time even on virtual environments including our test bot.
284   // For timing sensitive unittests, this function should be used.
285   static Time NowFromSystemTime();
286 
287   // Converts to/from time_t in UTC and a Time class.
288   // TODO(brettw) this should be removed once everybody starts using the |Time|
289   // class.
290   static Time FromTimeT(time_t tt);
291   time_t ToTimeT() const;
292 
293   // Converts time to/from a double which is the number of seconds since epoch
294   // (Jan 1, 1970).  Webkit uses this format to represent time.
295   // Because WebKit initializes double time value to 0 to indicate "not
296   // initialized", we map it to empty Time object that also means "not
297   // initialized".
298   static Time FromDoubleT(double dt);
299   double ToDoubleT() const;
300 
301 #if defined(OS_POSIX)
302   // Converts the timespec structure to time. MacOS X 10.8.3 (and tentatively,
303   // earlier versions) will have the |ts|'s tv_nsec component zeroed out,
304   // having a 1 second resolution, which agrees with
305   // https://developer.apple.com/legacy/library/#technotes/tn/tn1150.html#HFSPlusDates.
306   static Time FromTimeSpec(const timespec& ts);
307 #endif
308 
309   // Converts to/from the Javascript convention for times, a number of
310   // milliseconds since the epoch:
311   // https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getTime.
312   static Time FromJsTime(double ms_since_epoch);
313   double ToJsTime() const;
314 
315   // Converts to Java convention for times, a number of
316   // milliseconds since the epoch.
317   int64 ToJavaTime() const;
318 
319 #if defined(OS_POSIX)
320   static Time FromTimeVal(struct timeval t);
321   struct timeval ToTimeVal() const;
322 #endif
323 
324 #if defined(OS_MACOSX)
325   static Time FromCFAbsoluteTime(CFAbsoluteTime t);
326   CFAbsoluteTime ToCFAbsoluteTime() const;
327 #endif
328 
329 #if defined(OS_WIN)
330   static Time FromFileTime(FILETIME ft);
331   FILETIME ToFileTime() const;
332 
333   // The minimum time of a low resolution timer.  This is basically a windows
334   // constant of ~15.6ms.  While it does vary on some older OS versions, we'll
335   // treat it as static across all windows versions.
336   static const int kMinLowResolutionThresholdMs = 16;
337 
338   // Enable or disable Windows high resolution timer. If the high resolution
339   // timer is not enabled, calls to ActivateHighResolutionTimer will fail.
340   // When disabling the high resolution timer, this function will not cause
341   // the high resolution timer to be deactivated, but will prevent future
342   // activations.
343   // Must be called from the main thread.
344   // For more details see comments in time_win.cc.
345   static void EnableHighResolutionTimer(bool enable);
346 
347   // Activates or deactivates the high resolution timer based on the |activate|
348   // flag.  If the HighResolutionTimer is not Enabled (see
349   // EnableHighResolutionTimer), this function will return false.  Otherwise
350   // returns true.  Each successful activate call must be paired with a
351   // subsequent deactivate call.
352   // All callers to activate the high resolution timer must eventually call
353   // this function to deactivate the high resolution timer.
354   static bool ActivateHighResolutionTimer(bool activate);
355 
356   // Returns true if the high resolution timer is both enabled and activated.
357   // This is provided for testing only, and is not tracked in a thread-safe
358   // way.
359   static bool IsHighResolutionTimerInUse();
360 #endif
361 
362   // Converts an exploded structure representing either the local time or UTC
363   // into a Time class.
FromUTCExploded(const Exploded & exploded)364   static Time FromUTCExploded(const Exploded& exploded) {
365     return FromExploded(false, exploded);
366   }
FromLocalExploded(const Exploded & exploded)367   static Time FromLocalExploded(const Exploded& exploded) {
368     return FromExploded(true, exploded);
369   }
370 
371   // Converts an integer value representing Time to a class. This is used
372   // when deserializing a |Time| structure, using a value known to be
373   // compatible. It is not provided as a constructor because the integer type
374   // may be unclear from the perspective of a caller.
FromInternalValue(int64 us)375   static Time FromInternalValue(int64 us) {
376     return Time(us);
377   }
378 
379   // Converts a string representation of time to a Time object.
380   // An example of a time string which is converted is as below:-
381   // "Tue, 15 Nov 1994 12:45:26 GMT". If the timezone is not specified
382   // in the input string, FromString assumes local time and FromUTCString
383   // assumes UTC. A timezone that cannot be parsed (e.g. "UTC" which is not
384   // specified in RFC822) is treated as if the timezone is not specified.
385   // TODO(iyengar) Move the FromString/FromTimeT/ToTimeT/FromFileTime to
386   // a new time converter class.
FromString(const char * time_string,Time * parsed_time)387   static bool FromString(const char* time_string, Time* parsed_time) {
388     return FromStringInternal(time_string, true, parsed_time);
389   }
FromUTCString(const char * time_string,Time * parsed_time)390   static bool FromUTCString(const char* time_string, Time* parsed_time) {
391     return FromStringInternal(time_string, false, parsed_time);
392   }
393 
394   // For serializing, use FromInternalValue to reconstitute. Please don't use
395   // this and do arithmetic on it, as it is more error prone than using the
396   // provided operators.
ToInternalValue()397   int64 ToInternalValue() const {
398     return us_;
399   }
400 
401   // Fills the given exploded structure with either the local time or UTC from
402   // this time structure (containing UTC).
UTCExplode(Exploded * exploded)403   void UTCExplode(Exploded* exploded) const {
404     return Explode(false, exploded);
405   }
LocalExplode(Exploded * exploded)406   void LocalExplode(Exploded* exploded) const {
407     return Explode(true, exploded);
408   }
409 
410   // Rounds this time down to the nearest day in local time. It will represent
411   // midnight on that day.
412   Time LocalMidnight() const;
413 
414   Time& operator=(Time other) {
415     us_ = other.us_;
416     return *this;
417   }
418 
419   // Compute the difference between two times.
420   TimeDelta operator-(Time other) const {
421     return TimeDelta(us_ - other.us_);
422   }
423 
424   // Modify by some time delta.
425   Time& operator+=(TimeDelta delta) {
426     us_ += delta.delta_;
427     return *this;
428   }
429   Time& operator-=(TimeDelta delta) {
430     us_ -= delta.delta_;
431     return *this;
432   }
433 
434   // Return a new time modified by some delta.
435   Time operator+(TimeDelta delta) const {
436     return Time(us_ + delta.delta_);
437   }
438   Time operator-(TimeDelta delta) const {
439     return Time(us_ - delta.delta_);
440   }
441 
442   // Comparison operators
443   bool operator==(Time other) const {
444     return us_ == other.us_;
445   }
446   bool operator!=(Time other) const {
447     return us_ != other.us_;
448   }
449   bool operator<(Time other) const {
450     return us_ < other.us_;
451   }
452   bool operator<=(Time other) const {
453     return us_ <= other.us_;
454   }
455   bool operator>(Time other) const {
456     return us_ > other.us_;
457   }
458   bool operator>=(Time other) const {
459     return us_ >= other.us_;
460   }
461 
462  private:
463   friend class TimeDelta;
464 
Time(int64 us)465   explicit Time(int64 us) : us_(us) {
466   }
467 
468   // Explodes the given time to either local time |is_local = true| or UTC
469   // |is_local = false|.
470   void Explode(bool is_local, Exploded* exploded) const;
471 
472   // Unexplodes a given time assuming the source is either local time
473   // |is_local = true| or UTC |is_local = false|.
474   static Time FromExploded(bool is_local, const Exploded& exploded);
475 
476   // Converts a string representation of time to a Time object.
477   // An example of a time string which is converted is as below:-
478   // "Tue, 15 Nov 1994 12:45:26 GMT". If the timezone is not specified
479   // in the input string, local time |is_local = true| or
480   // UTC |is_local = false| is assumed. A timezone that cannot be parsed
481   // (e.g. "UTC" which is not specified in RFC822) is treated as if the
482   // timezone is not specified.
483   static bool FromStringInternal(const char* time_string,
484                                  bool is_local,
485                                  Time* parsed_time);
486 
487   // The representation of Jan 1, 1970 UTC in microseconds since the
488   // platform-dependent epoch.
489   static const int64 kTimeTToMicrosecondsOffset;
490 
491 #if defined(OS_WIN)
492   // Indicates whether fast timers are usable right now.  For instance,
493   // when using battery power, we might elect to prevent high speed timers
494   // which would draw more power.
495   static bool high_resolution_timer_enabled_;
496   // Count of activations on the high resolution timer.  Only use in tests
497   // which are single threaded.
498   static int high_resolution_timer_activated_;
499 #endif
500 
501   // Time in microseconds in UTC.
502   int64 us_;
503 };
504 
505 // Inline the TimeDelta factory methods, for fast TimeDelta construction.
506 
507 // static
FromDays(int days)508 inline TimeDelta TimeDelta::FromDays(int days) {
509   // Preserve max to prevent overflow.
510   if (days == std::numeric_limits<int>::max())
511     return Max();
512   return TimeDelta(days * Time::kMicrosecondsPerDay);
513 }
514 
515 // static
FromHours(int hours)516 inline TimeDelta TimeDelta::FromHours(int hours) {
517   // Preserve max to prevent overflow.
518   if (hours == std::numeric_limits<int>::max())
519     return Max();
520   return TimeDelta(hours * Time::kMicrosecondsPerHour);
521 }
522 
523 // static
FromMinutes(int minutes)524 inline TimeDelta TimeDelta::FromMinutes(int minutes) {
525   // Preserve max to prevent overflow.
526   if (minutes == std::numeric_limits<int>::max())
527     return Max();
528   return TimeDelta(minutes * Time::kMicrosecondsPerMinute);
529 }
530 
531 // static
FromSeconds(int64 secs)532 inline TimeDelta TimeDelta::FromSeconds(int64 secs) {
533   // Preserve max to prevent overflow.
534   if (secs == std::numeric_limits<int64>::max())
535     return Max();
536   return TimeDelta(secs * Time::kMicrosecondsPerSecond);
537 }
538 
539 // static
FromMilliseconds(int64 ms)540 inline TimeDelta TimeDelta::FromMilliseconds(int64 ms) {
541   // Preserve max to prevent overflow.
542   if (ms == std::numeric_limits<int64>::max())
543     return Max();
544   return TimeDelta(ms * Time::kMicrosecondsPerMillisecond);
545 }
546 
547 // static
FromSecondsD(double secs)548 inline TimeDelta TimeDelta::FromSecondsD(double secs) {
549   // Preserve max to prevent overflow.
550   if (secs == std::numeric_limits<double>::infinity())
551     return Max();
552   return TimeDelta(secs * Time::kMicrosecondsPerSecond);
553 }
554 
555 // static
FromMillisecondsD(double ms)556 inline TimeDelta TimeDelta::FromMillisecondsD(double ms) {
557   // Preserve max to prevent overflow.
558   if (ms == std::numeric_limits<double>::infinity())
559     return Max();
560   return TimeDelta(ms * Time::kMicrosecondsPerMillisecond);
561 }
562 
563 // static
FromMicroseconds(int64 us)564 inline TimeDelta TimeDelta::FromMicroseconds(int64 us) {
565   // Preserve max to prevent overflow.
566   if (us == std::numeric_limits<int64>::max())
567     return Max();
568   return TimeDelta(us);
569 }
570 
571 inline Time TimeDelta::operator+(Time t) const {
572   return Time(t.us_ + delta_);
573 }
574 
575 // TimeTicks ------------------------------------------------------------------
576 
577 class BASE_EXPORT TimeTicks {
578  public:
579   // We define this even without OS_CHROMEOS for seccomp sandbox testing.
580 #if defined(OS_LINUX)
581   // Force definition of the system trace clock; it is a chromeos-only api
582   // at the moment and surfacing it in the right place requires mucking
583   // with glibc et al.
584   static const clockid_t kClockSystemTrace = 11;
585 #endif
586 
TimeTicks()587   TimeTicks() : ticks_(0) {
588   }
589 
590   // Platform-dependent tick count representing "right now."
591   // The resolution of this clock is ~1-15ms.  Resolution varies depending
592   // on hardware/operating system configuration.
593   static TimeTicks Now();
594 
595   // Returns a platform-dependent high-resolution tick count. Implementation
596   // is hardware dependent and may or may not return sub-millisecond
597   // resolution.  THIS CALL IS GENERALLY MUCH MORE EXPENSIVE THAN Now() AND
598   // SHOULD ONLY BE USED WHEN IT IS REALLY NEEDED.
599   static TimeTicks HighResNow();
600 
601   static bool IsHighResNowFastAndReliable();
602 
603   // Returns true if ThreadNow() is supported on this system.
IsThreadNowSupported()604   static bool IsThreadNowSupported() {
605 #if (defined(_POSIX_THREAD_CPUTIME) && (_POSIX_THREAD_CPUTIME >= 0)) || \
606     (defined(OS_MACOSX) && !defined(OS_IOS)) || defined(OS_ANDROID)
607     return true;
608 #else
609     return false;
610 #endif
611   }
612 
613   // Returns thread-specific CPU-time on systems that support this feature.
614   // Needs to be guarded with a call to IsThreadNowSupported(). Use this timer
615   // to (approximately) measure how much time the calling thread spent doing
616   // actual work vs. being de-scheduled. May return bogus results if the thread
617   // migrates to another CPU between two calls.
618   static TimeTicks ThreadNow();
619 
620   // Returns the current system trace time or, if none is defined, the current
621   // high-res time (i.e. HighResNow()). On systems where a global trace clock
622   // is defined, timestamping TraceEvents's with this value guarantees
623   // synchronization between events collected inside chrome and events
624   // collected outside (e.g. kernel, X server).
625   static TimeTicks NowFromSystemTraceTime();
626 
627 #if defined(OS_WIN)
628   // Get the absolute value of QPC time drift. For testing.
629   static int64 GetQPCDriftMicroseconds();
630 
631   static TimeTicks FromQPCValue(LONGLONG qpc_value);
632 
633   // Returns true if the high resolution clock is working on this system.
634   // This is only for testing.
635   static bool IsHighResClockWorking();
636 
637   // Enable high resolution time for TimeTicks::Now(). This function will
638   // test for the availability of a working implementation of
639   // QueryPerformanceCounter(). If one is not available, this function does
640   // nothing and the resolution of Now() remains 1ms. Otherwise, all future
641   // calls to TimeTicks::Now() will have the higher resolution provided by QPC.
642   // Returns true if high resolution time was successfully enabled.
643   static bool SetNowIsHighResNowIfSupported();
644 
645   // Returns a time value that is NOT rollover protected.
646   static TimeTicks UnprotectedNow();
647 #endif
648 
649   // Returns true if this object has not been initialized.
is_null()650   bool is_null() const {
651     return ticks_ == 0;
652   }
653 
654   // Converts an integer value representing TimeTicks to a class. This is used
655   // when deserializing a |TimeTicks| structure, using a value known to be
656   // compatible. It is not provided as a constructor because the integer type
657   // may be unclear from the perspective of a caller.
FromInternalValue(int64 ticks)658   static TimeTicks FromInternalValue(int64 ticks) {
659     return TimeTicks(ticks);
660   }
661 
662   // Get the TimeTick value at the time of the UnixEpoch. This is useful when
663   // you need to relate the value of TimeTicks to a real time and date.
664   // Note: Upon first invocation, this function takes a snapshot of the realtime
665   // clock to establish a reference point.  This function will return the same
666   // value for the duration of the application, but will be different in future
667   // application runs.
668   static TimeTicks UnixEpoch();
669 
670   // Returns the internal numeric value of the TimeTicks object.
671   // For serializing, use FromInternalValue to reconstitute.
ToInternalValue()672   int64 ToInternalValue() const {
673     return ticks_;
674   }
675 
676   TimeTicks& operator=(TimeTicks other) {
677     ticks_ = other.ticks_;
678     return *this;
679   }
680 
681   // Compute the difference between two times.
682   TimeDelta operator-(TimeTicks other) const {
683     return TimeDelta(ticks_ - other.ticks_);
684   }
685 
686   // Modify by some time delta.
687   TimeTicks& operator+=(TimeDelta delta) {
688     ticks_ += delta.delta_;
689     return *this;
690   }
691   TimeTicks& operator-=(TimeDelta delta) {
692     ticks_ -= delta.delta_;
693     return *this;
694   }
695 
696   // Return a new TimeTicks modified by some delta.
697   TimeTicks operator+(TimeDelta delta) const {
698     return TimeTicks(ticks_ + delta.delta_);
699   }
700   TimeTicks operator-(TimeDelta delta) const {
701     return TimeTicks(ticks_ - delta.delta_);
702   }
703 
704   // Comparison operators
705   bool operator==(TimeTicks other) const {
706     return ticks_ == other.ticks_;
707   }
708   bool operator!=(TimeTicks other) const {
709     return ticks_ != other.ticks_;
710   }
711   bool operator<(TimeTicks other) const {
712     return ticks_ < other.ticks_;
713   }
714   bool operator<=(TimeTicks other) const {
715     return ticks_ <= other.ticks_;
716   }
717   bool operator>(TimeTicks other) const {
718     return ticks_ > other.ticks_;
719   }
720   bool operator>=(TimeTicks other) const {
721     return ticks_ >= other.ticks_;
722   }
723 
724  protected:
725   friend class TimeDelta;
726 
727   // Please use Now() to create a new object. This is for internal use
728   // and testing. Ticks is in microseconds.
TimeTicks(int64 ticks)729   explicit TimeTicks(int64 ticks) : ticks_(ticks) {
730   }
731 
732   // Tick count in microseconds.
733   int64 ticks_;
734 
735 #if defined(OS_WIN)
736   typedef DWORD (*TickFunctionType)(void);
737   static TickFunctionType SetMockTickFunction(TickFunctionType ticker);
738 #endif
739 };
740 
741 inline TimeTicks TimeDelta::operator+(TimeTicks t) const {
742   return TimeTicks(t.ticks_ + delta_);
743 }
744 
745 }  // namespace base
746 
747 #endif  // BASE_TIME_TIME_H_
748