Measure bandwidth for chromoting video channel

remoting/base/running_average.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// RunningAverage defined in this file is used to generate statistics for
+// bandwidth, latency and other performance metrics for remoting. Usually
+// these data come in as a stream and fluctuates a lot. They are processed by
+// this class to generate a more stable value by taking average within a
+// window of data points.
+
+// TimedRunningAverage keeps track of running average in a timed faction.

[simonmorris, 2011/03/25 09:24:59]

"Fashion" instead of "faction"?

+// It essentially reports the rate of RunningAverage divided by the duration
+// of the window.
+
+// All classes defined are thread-safe.
+
+#ifndef REMOTING_BASE_RUNNING_AVERAGE_H_
+#define REMOTING_BASE_RUNNING_AVERAGE_H_
+
+#include <deque>
+
+#include "base/basictypes.h"
+#include "base/synchronization/lock.h"
+#include "base/time.h"
+
+namespace remoting {
+
+class RunningAverage {
+ public:
+  // Construct a running average counter for a specific window size. The most

[simonmorris, 2011/03/25 09:24:59]

"|windows_size| most"

+  // |windows_size| recent values are kept and the average is reported.
+  RunningAverage(int window_size);
+
+  virtual ~RunningAverage();
+
+  // Record the provided data point.
+  void Record(int64 value);
+
+  // Return the average of data points in the last window.
+  int64 Average();
+
+ private:
+  // Size of the window. This is of type size_t to avoid casting when comparing
+  // with the size of |data_points_|.
+  size_t window_size_;
+
+  // Protects |data_points_| and |sum_|.
+  base::Lock lock_;
+
+  // Keep the values of all the data points.
+  std::deque<int64> data_points_;
+
+  // Sum of values in |data_points_|.
+  int64 sum_;
+
+  DISALLOW_COPY_AND_ASSIGN(RunningAverage);
+};
+
+class TimedRunningAverage {
+ public:
+  // Construct with a window size.
+  TimedRunningAverage(int window_size);

[simonmorris, 2011/03/25 09:24:59]

Is it better for the window to be a length of time, instead
of a number of samples? For example, consider the case where
big buffers mean that many packets are delivered at the same
time.

+
+  virtual ~TimedRunningAverage();
+
+  // Record the value and the current time.
+  void Record(int64 value);
+
+  // Report the rate per second recorded.
+  double Rate();
+
+ private:
+  // Protects |time_|.
+  base::Lock lock_;
+
+  // Timestamps when Record() is called.
+  std::deque<base::Time> time_;
+
+  // Counter to measure the running average.
+  RunningAverage counter_;
+
+  // Window size for the rate.
+  size_t window_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(TimedRunningAverage);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_BASE_RUNNING_AVERAGE_H_