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
11namespace v8 {
12namespace base {
13
14class 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(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(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 v8::base
96
97#endif  // V8_BASE_PLATFORM_ELAPSED_TIMER_H_
98