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1 /* | |
2 * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved. | |
3 * | |
4 * Use of this source code is governed by a BSD-style license | |
5 * that can be found in the LICENSE file in the root of the source | |
6 * tree. An additional intellectual property rights grant can be found | |
7 * in the file PATENTS. All contributing project authors may | |
8 * be found in the AUTHORS file in the root of the source tree. | |
9 */ | |
10 | |
11 #ifndef WEBRTC_RTC_BASE_MOVING_MAX_COUNTER_H_ | |
12 #define WEBRTC_RTC_BASE_MOVING_MAX_COUNTER_H_ | |
13 | |
14 #include <stdint.h> | |
15 | |
16 #include <deque> | |
17 #include <limits> | |
18 #include <utility> | |
19 | |
20 #include "webrtc/rtc_base/checks.h" | |
21 #include "webrtc/rtc_base/constructormagic.h" | |
22 #include "webrtc/rtc_base/optional.h" | |
23 | |
24 namespace rtc { | |
25 | |
26 // Implements moving max: can add samples to it and calculate maximum over some | |
27 // fixed moving window. | |
28 // | |
29 // Window size is configured at constructor. | |
30 // Samples can be added with |Add()| and max over current window is returned by | |
31 // |MovingMax|. |current_time_ms| in successive calls to Add and MovingMax | |
32 // should never decrease as if it's a wallclock time. | |
33 // Not thread-safe even if you only call const methods. | |
34 template <class T> | |
35 class MovingMaxCounter { | |
36 public: | |
37 explicit MovingMaxCounter(int64_t window_length_ms); | |
38 // Advances the current time, and adds a new sample. The new current time must | |
39 // be at least as large as the old current time. | |
40 void Add(const T& sample, int64_t current_time_ms); | |
41 // Advances the current time, and returns the maximum sample in the time | |
42 // window ending at the current time. The new current time must be at least as | |
43 // large as the old current time. | |
44 rtc::Optional<T> Max(int64_t current_time_ms) const; | |
45 void Reset(); | |
46 | |
47 private: | |
48 // Throws out obsolete samples. Is |const| because it is always safe to throw | |
49 // out old elements as long as |current_time_ms| parameters to public methods | |
50 // are always increasing. | |
51 void RollWindow(int64_t new_time_ms) const; | |
52 const int64_t window_length_ms_; | |
53 // Samples in the window are stored as pairs <time, sample> in this deque in | |
54 // chronological order. Samples what can't be maximum in any window are | |
55 // thrown out - deque always contains non-increasing sequence of samples. | |
56 // Is |mutable| because |MovingMax()| may be called on const instances yet it | |
57 // will remove obsolete samples to speed up consecutive calls. | |
58 mutable std::deque<std::pair<int64_t, T>> samples_; | |
59 #if RTC_DCHECK_IS_ON | |
60 mutable int64_t last_call_time_ms_; | |
61 #endif | |
62 RTC_DISALLOW_COPY_AND_ASSIGN(MovingMaxCounter); | |
63 }; | |
64 | |
65 template <class T> | |
66 MovingMaxCounter<T>::MovingMaxCounter(int64_t window_length_ms) | |
67 : window_length_ms_(window_length_ms) | |
68 #if RTC_DCHECK_IS_ON | |
69 , last_call_time_ms_(std::numeric_limits<int64_t>::min()) | |
70 #endif | |
kwiberg-webrtc
2017/08/22 13:28:41
I think the compiler will complain about a misplac
ilnik
2017/08/22 14:11:34
It doesn't complain locally. Waiting for the trybo
ilnik
2017/08/22 16:12:44
Bots do not complain too.
kwiberg-webrtc
2017/08/22 21:40:46
Agh, it's just me who can't read. The parentheses
ilnik
2017/08/23 07:46:50
Yes, it might be more readable that way. Changing
| |
71 {} | |
72 | |
73 template <class T> | |
74 void MovingMaxCounter<T>::Add(const T& sample, int64_t current_time_ms) { | |
75 #if RTC_DCHECK_IS_ON | |
76 RTC_DCHECK_GE(current_time_ms, last_call_time_ms_); | |
77 last_call_time_ms_ = current_time_ms; | |
78 #endif | |
79 RollWindow(current_time_ms); | |
80 // Remove samples what will never be maximum in any window: newly added sample | |
81 // will always be in all windows the previous samples are. Thus, smaller | |
82 // samples could be removed. This will maintain the invariant - deque contains | |
83 // non-increasing sequence of values. | |
84 while (!samples_.empty() && samples_.back().second < sample) { | |
85 samples_.pop_back(); | |
86 } | |
87 // Add the new sample but only if there's no existing sample at the same time. | |
88 // Due to checks above, already existing element will be larger and new sample | |
89 // will never be a maximum in any window. | |
90 if (samples_.empty() || samples_.back().first < current_time_ms) { | |
91 samples_.emplace_back(std::make_pair(current_time_ms, sample)); | |
92 } | |
93 } | |
94 | |
95 template <class T> | |
96 rtc::Optional<T> MovingMaxCounter<T>::Max(int64_t current_time_ms) const { | |
97 #if RTC_DCHECK_IS_ON | |
98 RTC_DCHECK_GE(current_time_ms, last_call_time_ms_); | |
99 last_call_time_ms_ = current_time_ms; | |
100 #endif | |
101 RollWindow(current_time_ms); | |
102 rtc::Optional<T> res; | |
103 if (!samples_.empty()) { | |
104 res.emplace(samples_.front().second); | |
105 } | |
106 return res; | |
107 } | |
108 | |
109 template <class T> | |
110 void MovingMaxCounter<T>::Reset() { | |
111 samples_.clear(); | |
112 } | |
113 | |
114 template <class T> | |
115 void MovingMaxCounter<T>::RollWindow(int64_t new_time_ms) const { | |
116 const int64_t window_begin_ms = new_time_ms - window_length_ms_; | |
117 auto it = samples_.begin(); | |
118 while (it != samples_.end() && it->first < window_begin_ms) { | |
119 ++it; | |
120 } | |
121 samples_.erase(samples_.begin(), it); | |
122 } | |
123 | |
124 } // namespace rtc | |
125 | |
126 #endif // WEBRTC_RTC_BASE_MOVING_MAX_COUNTER_H_ | |
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