V8 API Reference, 7.2.502.16 (for Deno 0.2.4)
elapsed-timer.h
1 // Copyright 2013 the V8 project 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 #ifndef V8_BASE_PLATFORM_ELAPSED_TIMER_H_
6 #define V8_BASE_PLATFORM_ELAPSED_TIMER_H_
7 
8 #include "src/base/logging.h"
9 #include "src/base/platform/time.h"
10 
11 namespace v8 {
12 namespace base {
13 
14 class ElapsedTimer final {
15  public:
16 #ifdef DEBUG
17  ElapsedTimer() : started_(false) {}
18 #endif
19 
20  // Starts this timer. Once started a timer can be checked with
21  // |Elapsed()| or |HasExpired()|, and may be restarted using |Restart()|.
22  // This method must not be called on an already started timer.
23  void Start() {
24  DCHECK(!IsStarted());
25  start_ticks_ = Now();
26 #ifdef DEBUG
27  started_ = true;
28 #endif
29  DCHECK(IsStarted());
30  }
31 
32  // Stops this timer. Must not be called on a timer that was not
33  // started before.
34  void Stop() {
35  DCHECK(IsStarted());
36  start_ticks_ = TimeTicks();
37 #ifdef DEBUG
38  started_ = false;
39 #endif
40  DCHECK(!IsStarted());
41  }
42 
43  // Returns |true| if this timer was started previously.
44  bool IsStarted() const {
45  DCHECK(started_ || start_ticks_.IsNull());
46  DCHECK(!started_ || !start_ticks_.IsNull());
47  return !start_ticks_.IsNull();
48  }
49 
50  // Restarts the timer and returns the time elapsed since the previous start.
51  // This method is equivalent to obtaining the elapsed time with |Elapsed()|
52  // and then starting the timer again, but does so in one single operation,
53  // avoiding the need to obtain the clock value twice. It may only be called
54  // on a previously started timer.
55  TimeDelta Restart() {
56  DCHECK(IsStarted());
57  TimeTicks ticks = Now();
58  TimeDelta elapsed = ticks - start_ticks_;
59  DCHECK_GE(elapsed.InMicroseconds(), 0);
60  start_ticks_ = ticks;
61  DCHECK(IsStarted());
62  return elapsed;
63  }
64 
65  // Returns the time elapsed since the previous start. This method may only
66  // be called on a previously started timer.
67  TimeDelta Elapsed() const {
68  DCHECK(IsStarted());
69  TimeDelta elapsed = Now() - start_ticks_;
70  DCHECK_GE(elapsed.InMicroseconds(), 0);
71  return elapsed;
72  }
73 
74  // Returns |true| if the specified |time_delta| has elapsed since the
75  // previous start, or |false| if not. This method may only be called on
76  // a previously started timer.
77  bool HasExpired(TimeDelta time_delta) const {
78  DCHECK(IsStarted());
79  return Elapsed() >= time_delta;
80  }
81 
82  private:
83  static V8_INLINE TimeTicks Now() {
84  TimeTicks now = TimeTicks::HighResolutionNow();
85  DCHECK(!now.IsNull());
86  return now;
87  }
88 
89  TimeTicks start_ticks_;
90 #ifdef DEBUG
91  bool started_;
92 #endif
93 };
94 
95 } // namespace base
96 } // namespace v8
97 
98 #endif // V8_BASE_PLATFORM_ELAPSED_TIMER_H_
Definition: libplatform.h:13