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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 template <class T> | |
34 class MovingMaxCounter { | |
35 public: | |
36 explicit MovingMaxCounter(int64_t window_length_ms); | |
37 // Advances the current time, and adds a new sample. The new current time must | |
38 // be at least as large as the old current time. | |
39 void Add(const T& sample, int64_t current_time_ms); | |
40 // Advances the current time, and returns the maximum sample in the time | |
41 // window ending at the current time. The new current time must be at least as | |
42 // large as the old current time. | |
43 rtc::Optional<T> Max(int64_t current_time_ms); | |
44 void Reset(); | |
45 | |
46 private: | |
47 // Throws out obsolete samples. | |
48 void RollWindow(int64_t new_time_ms); | |
49 const int64_t window_length_ms_; | |
50 // This deque stores (timestamp, sample) pairs in chronological order; new | |
51 // pairs are only ever added at the end. However, because they can't affect | |
52 // the Max() calculation, pairs older than window_length_ms_ are discarded, | |
53 // and if an older pair has a sample that's smaller than that of a younger | |
54 // pair, the older pair is discarded. As a result, the sequence of timestamps | |
55 // is non-decreasing, and the sequence of samples is decreasing. | |
kwiberg-webrtc
2017/08/23 10:33:33
decreasing -> strictly decreasing
ilnik
2017/08/23 11:26:12
Done.
| |
56 std::deque<std::pair<int64_t, T>> samples_; | |
57 #if RTC_DCHECK_IS_ON | |
58 int64_t last_call_time_ms_ = std::numeric_limits<int64_t>::min(); | |
59 #endif | |
60 RTC_DISALLOW_COPY_AND_ASSIGN(MovingMaxCounter); | |
61 }; | |
62 | |
63 template <class T> | |
64 MovingMaxCounter<T>::MovingMaxCounter(int64_t window_length_ms) | |
65 : window_length_ms_(window_length_ms) {} | |
66 | |
67 template <class T> | |
68 void MovingMaxCounter<T>::Add(const T& sample, int64_t current_time_ms) { | |
69 RollWindow(current_time_ms); | |
70 // Remove samples that will never be maximum in any window: newly added sample | |
71 // will always be in all windows the previous samples are. Thus, smaller or | |
72 // equal samples could be removed. This will maintain the invariant - deque | |
73 // contains decreasing sequence of values. | |
kwiberg-webrtc
2017/08/23 10:33:33
contains a strictly decreasing sequence of values.
ilnik
2017/08/23 11:26:12
Done.
| |
74 while (!samples_.empty() && samples_.back().second <= sample) { | |
75 samples_.pop_back(); | |
76 } | |
77 // Add the new sample but only if there's no existing sample at the same time. | |
78 // Due to checks above, already existing element will be larger and new sample | |
79 // will never be a maximum in any window. | |
kwiberg-webrtc
2017/08/23 10:33:33
Due to the checks above, the already existing elem
ilnik
2017/08/23 11:26:12
Rephrased a little.
| |
80 if (samples_.empty() || samples_.back().first < current_time_ms) { | |
81 samples_.emplace_back(std::make_pair(current_time_ms, sample)); | |
82 } | |
83 } | |
84 | |
85 template <class T> | |
86 rtc::Optional<T> MovingMaxCounter<T>::Max(int64_t current_time_ms) { | |
87 RollWindow(current_time_ms); | |
88 rtc::Optional<T> res; | |
89 if (!samples_.empty()) { | |
90 res.emplace(samples_.front().second); | |
91 } | |
92 return res; | |
93 } | |
94 | |
95 template <class T> | |
96 void MovingMaxCounter<T>::Reset() { | |
97 samples_.clear(); | |
98 } | |
99 | |
100 template <class T> | |
101 void MovingMaxCounter<T>::RollWindow(int64_t new_time_ms) { | |
102 #if RTC_DCHECK_IS_ON | |
103 RTC_DCHECK_GE(new_time_ms, last_call_time_ms_); | |
104 last_call_time_ms_ = new_time_ms; | |
105 #endif | |
106 const int64_t window_begin_ms = new_time_ms - window_length_ms_; | |
107 auto it = samples_.begin(); | |
108 while (it != samples_.end() && it->first < window_begin_ms) { | |
109 ++it; | |
110 } | |
111 samples_.erase(samples_.begin(), it); | |
112 } | |
113 | |
114 } // namespace rtc | |
115 | |
116 #endif // WEBRTC_RTC_BASE_MOVING_MAX_COUNTER_H_ | |
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