Add class which periodically computes statistics.

webrtc/video/stats_counter.h

Index: webrtc/video/stats_counter.h
diff --git a/webrtc/video/stats_counter.h b/webrtc/video/stats_counter.h
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+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_VIDEO_STATS_COUNTER_H_
+#define WEBRTC_VIDEO_STATS_COUNTER_H_
+
+#include <memory>
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/typedefs.h"
+
+namespace webrtc {
+
+class AggregatedCounter;
+class Clock;
+
+// |StatsCounterObserver| is called periodically when a metric is updated.
+class StatsCounterObserver {
+ public:
+  virtual void OnMetricUpdated(int sample) = 0;
+
+  virtual ~StatsCounterObserver() {}
+};
+
+struct AggregatedStats {
+  int64_t num_samples = 0;
+  int min = -1;
+  int max = -1;
+  int average = -1;
+  // TODO(asapersson): Consider adding median/percentiles.
+};
+
+// Classes which periodically computes a metric.
+//
+// During a period, |kProcessIntervalMs|, different metrics can be computed e.g:
+// - |AvgCounter|: average of samples
+// - |PercentCounter|: percentage of samples
+// - |PermilleCounter|: permille of samples
+//
+// Each periodic metric can be either:
+// - reported to an |observer| each period
+// - aggregated during the call (e.g. min, max, average)
+//
+//                 periodically computed
+//                    GetMetric()            GetMetric()   => AggregatedStats
+//                        ^                      ^            (e.g. min/max/avg)
+//                        |                      |
+// |   *    *  *       *  |  **    *   * *     * | ...
+// |<- process interval ->|
+//
+// (*) - samples
+//
+//
+// Example usage:
+//
+// AvgCounter counter(&clock, nullptr);
+// counter.Add(5);
+// counter.Add(1);
+// counter.Add(6);   // process interval passed -> GetMetric() avg:4
+// counter.Add(7);
+// counter.Add(3);   // process interval passed -> GetMetric() avg:5
+// counter.Add(10);
+// counter.Add(20);  // process interval passed -> GetMetric() avg:15
+// AggregatedStats stats = counter.GetStats();
+// stats: {min:4, max:15, avg:8}
+//
+
+// Note: StatsCounter takes ownership of |observer|.
+
+class StatsCounter {
+ public:
+  virtual ~StatsCounter();
+
+  virtual bool GetMetric(int* metric) const = 0;
+
+  AggregatedStats GetStats();
+
+ protected:
+  StatsCounter(Clock* clock,
+               bool include_empty_intervals,
+               StatsCounterObserver* observer);
+
+  void Add(int sample);
+  void Set(int sample);
+
+  int max_;
+  int64_t sum_;
+  int64_t num_samples_;
+  int64_t last_sum_;
+
+ private:
+  bool TimeToProcess();
+  void TryProcess();
+
+  Clock* const clock_;
+  const bool include_empty_intervals_;
+  const std::unique_ptr<StatsCounterObserver> observer_;
+  const std::unique_ptr<AggregatedCounter> aggregated_counter_;
+  int64_t last_process_time_ms_;
+};
+
+// AvgCounter: average of samples
+//
+//           | *      *      *      | *           *       | ...
+//           | Add(5) Add(1) Add(6) | Add(5)      Add(5)  |
+// GetMetric | (5 + 1 + 6) / 3      | (5 + 5) / 2         |
+//
+class AvgCounter : public StatsCounter {
+ public:
+  AvgCounter(Clock* clock, StatsCounterObserver* observer);
+  ~AvgCounter() override {}
+
+  void Add(int sample);
+
+ private:
+  bool GetMetric(int* metric) const override;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(AvgCounter);
+};
+
+// MaxCounter: maximum of samples
+//
+//           | *      *      *      | *           *       | ...
+//           | Add(5) Add(1) Add(6) | Add(5)      Add(5)  |
+// GetMetric | max: (5, 1, 6)       | max: (5, 5)         |
+//
+class MaxCounter : public StatsCounter {
+ public:
+  MaxCounter(Clock* clock, StatsCounterObserver* observer);
+  ~MaxCounter() override {}
+
+  void Add(int sample);
+
+ private:
+  bool GetMetric(int* metric) const override;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(MaxCounter);
+};
+
+// PercentCounter: percentage of samples
+//
+//           | *      *      *      | *           *       | ...
+//           | Add(T) Add(F) Add(T) | Add(F)      Add(T)  |
+// GetMetric | 100 * 2 / 3          | 100 * 1 / 2         |
+//
+class PercentCounter : public StatsCounter {
+ public:
+  PercentCounter(Clock* clock, StatsCounterObserver* observer);
+  ~PercentCounter() override {}
+
+  void Add(bool sample);
+
+ private:
+  bool GetMetric(int* metric) const override;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(PercentCounter);
+};
+
+// PermilleCounter: permille of samples
+//
+//           | *      *      *      | *         *         | ...
+//           | Add(T) Add(F) Add(T) | Add(F)    Add(T)    |
+// GetMetric | 1000 *  2 / 3        | 1000 * 1 / 2        |
+//
+class PermilleCounter : public StatsCounter {
+ public:
+  PermilleCounter(Clock* clock, StatsCounterObserver* observer);
+  ~PermilleCounter() override {}
+
+  void Add(bool sample);
+
+ private:
+  bool GetMetric(int* metric) const override;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(PermilleCounter);
+};
+
+// RateCounter: units per second
+//
+//           | *      *      *      | *           *       | ...
+//           | Add(5) Add(1) Add(6) | Add(5)      Add(5)  |
+//           |<------ 2 sec ------->|                     |
+// GetMetric | (5 + 1 + 6) / 2      | (5 + 5) / 2         |
+//
+class RateCounter : public StatsCounter {
+ public:
+  RateCounter(Clock* clock, StatsCounterObserver* observer);
+  ~RateCounter() override {}
+
+  void Add(int sample);
+
+ private:
+  bool GetMetric(int* metric) const override;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(RateCounter);
+};
+
+// RateAccCounter: units per second (used for counters)
+//
+//           | *      *      *      | *         *         | ...
+//           | Set(5) Set(6) Set(8) | Set(11)   Set(13)   |
+//           |<------ 2 sec ------->|                     |
+// GetMetric | 8 / 2                | (13 - 8) / 2        |
+//
+class RateAccCounter : public StatsCounter {
+ public:
+  RateAccCounter(Clock* clock, StatsCounterObserver* observer);
+  ~RateAccCounter() override {}
+
+  void Set(int sample);
+
+ private:
+  bool GetMetric(int* metric) const override;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(RateAccCounter);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_VIDEO_STATS_COUNTER_H_