Measure bandwidth for chromoting video channel

remoting/base/running_average.cc

+// 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.
+
+#include "base/logging.h"
+#include "remoting/base/running_average.h"
+
+namespace remoting {
+
+RunningAverage::RunningAverage(int window_size)
+    : window_size_(window_size),
+      sum_(0) {
+  CHECK(window_size_);
+}
+
+RunningAverage::~RunningAverage() {
+}
+
+void RunningAverage::Record(int64 value) {
+  base::AutoLock auto_lock(lock_);
+
+  data_points_.push_back(value);
+  sum_ += value;
+
+  if (data_points_.size() > window_size_) {
+    sum_ -= data_points_[0];
+    data_points_.pop_front();
+  }
+}
+
+int64 RunningAverage::Average() {
+  base::AutoLock auto_lock(lock_);
+
+  if (data_points_.empty())
+    return 0;
+  return sum_ / data_points_.size();
+}
+
+TimedRunningAverage::TimedRunningAverage(int window_size)
+    : counter_(window_size),
+      window_size_(window_size) {
+}
+
+TimedRunningAverage::~TimedRunningAverage() {
+}
+
+void TimedRunningAverage::Record(int64 value) {
+  {
+    base::AutoLock auto_lock(lock_);
+    time_.push_back(base::Time::Now());
+
+    if (time_.size() > window_size_)
+      time_.pop_front();
+  }
+  counter_.Record(value);
+}
+
+double TimedRunningAverage::Rate() {
+  int64 average = counter_.Average();
+  base::TimeDelta delta;
+
+  {
+    base::AutoLock auto_lock(lock_);
+    if (!time_.empty())
+      delta = *time_.rbegin() - *time_.begin();
+  }
+
+  if (delta.InMilliseconds())
+    return 1000.0 * average / delta.InMilliseconds();

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

I'm not sure the math is right here. For a rate, don't you
want total_bytes/total_time, not
average_bytes_per_packet/total_time? And if data_points[i]
is the number of bytes delivered between time[i-1] and
time[i], shouldn't the sum of data_points[i] (0 <= i < n)
be compared to time[n-1] - time[-1]? Maybe one class would
be simpler than two here.

[Wez, 2011/03/25 10:43:19]

Yes.  The rate (bandwidth in our case) would normally just be bytes_in_interval
/ second_in_interval.

It's also conventional to have exponential drop-off for bandwidth estimates of
this sort, so that if you happen to sample close to a sudden spike or trough in
traffic you don't get misleading values.

+  return 0;
+}
+
+}  // namespace remoting