Add a rate tracker that tracks rate over a given interval split up into buckets that accumulate uni…

webrtc/base/ratetracker.h

Index: webrtc/base/ratetracker.h
diff --git a/webrtc/base/ratetracker.h b/webrtc/base/ratetracker.h
index 575bff75a46e62738b330b06f3a1bc9b6e316d96..317dd9b99347f5118cbb1f1e1b866c9165f86cd0 100644
--- a/webrtc/base/ratetracker.h
+++ b/webrtc/base/ratetracker.h
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
+ *  Copyright 2015 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
@@ -16,25 +16,45 @@
 
 namespace rtc {
 
-// Computes instantaneous units per second.
+// Computes units per second over a given interval by tracking the units over
+// each bucket of a given size and calculating the instantaneous rate assuming
+// that over each bucket the rate was constant.
 class RateTracker {
  public:
-  RateTracker();
-  virtual ~RateTracker() {}
+  RateTracker(uint32 bucket_milliseconds, size_t bucket_count);
+  virtual ~RateTracker();
 
-  size_t total_units() const;
-  size_t units_second();
-  void Update(size_t units);
+  double ComputeCurrentRate(uint32 interval_milliseconds) const;
+  double ComputeCurrentRate() const {

[noahric, 2015/09/03 21:42:24]

Use a different name for these; C++ style guide frowns on overloads. So maybe:
ComputeRateForInterval(uint32 interval_milliseconds)
ComputeRate()

[tpsiaki, 2015/09/03 23:28:59]

Done.

+    return ComputeCurrentRate(
+        bucket_milliseconds_ * static_cast<uint32>(bucket_count_));
+  }
+
+  // Computes the average rate over the lifetime of the rate tracker.

[noahric, 2015/09/03 21:42:24]

I'd replace "lifetime" with "since the first sample was added to the rate
tracker". Also add comments for both ComputeCurrentRate, especially to
distinguish the arg-less one from this method.

[tpsiaki, 2015/09/03 23:28:59]

Done.

+  double ComputeTotalRate() const;
+
+  // The total number of samples added.
+  size_t TotalSampleCount() const;
+
+  // Reads the current time in order to determine the appropriate bucket for
+  // these samples, and increments the count for that bucket by sample_count.
+  void AddSamples(size_t sample_count);
 
  protected:
   // overrideable for tests
   virtual uint32 Time() const;
 
  private:
-  size_t total_units_;
-  size_t units_second_;
-  uint32 last_units_second_time_;
-  size_t last_units_second_calc_;
+  void EnsureInitialized();
+  size_t NextBucketIndex(size_t bucket_index) const;
+
+  const uint32 bucket_milliseconds_;
+  const size_t bucket_count_;
+  size_t* sample_buckets_;
+  size_t total_sample_count_;
+  size_t current_bucket_;
+  uint32 bucket_start_time_;

[noahric, 2015/09/03 21:42:24]

Prefer these have units as well (millis, ms, or milliseconds).

[tpsiaki, 2015/09/03 23:28:59]

Done.

+  uint32 initialization_time_;
 };
 
 }  // namespace rtc