dom/media/MediaChannelStatistics.h

   1 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #if !defined(MediaChannelStatistics_h_)
   7 #  define MediaChannelStatistics_h_
   8
   9 #  include "mozilla/TimeStamp.h"
  10
  11 namespace mozilla {
  12
  13 // Number of bytes we have accumulated before we assume the connection download
  14 // rate can be reliably calculated. 57 Segments at IW=3 allows slow start to
  15 // reach a CWND of 30 (See bug 831998)
  16 static const int64_t RELIABLE_DATA_THRESHOLD = 57 * 1460;
  17
  18 /**
  19  * This class is useful for estimating rates of data passing through
  20  * some channel. The idea is that activity on the channel "starts"
  21  * and "stops" over time. At certain times data passes through the
  22  * channel (usually while the channel is active; data passing through
  23  * an inactive channel is ignored). The GetRate() function computes
  24  * an estimate of the "current rate" of the channel, which is some
  25  * kind of average of the data passing through over the time the
  26  * channel is active.
  27  *
  28  * All methods take "now" as a parameter so the user of this class can
  29  * control the timeline used.
  30  */
  31 class MediaChannelStatistics {
  32  public:
  33   MediaChannelStatistics() = default;
  34   MediaChannelStatistics(const MediaChannelStatistics&) = default;
  35   MediaChannelStatistics& operator=(const MediaChannelStatistics&) = default;
  36
  37   void Reset() {
  38     mLastStartTime = TimeStamp();
  39     mAccumulatedTime = TimeDuration(0);
  40     mAccumulatedBytes = 0;
  41     mIsStarted = false;
  42   }
  43   void Start() {
  44     if (mIsStarted) return;
  45     mLastStartTime = TimeStamp::Now();
  46     mIsStarted = true;
  47   }
  48   void Stop() {
  49     if (!mIsStarted) return;
  50     mAccumulatedTime += TimeStamp::Now() - mLastStartTime;
  51     mIsStarted = false;
  52   }
  53   void AddBytes(int64_t aBytes) {
  54     if (!mIsStarted) {
  55       // ignore this data, it may be related to seeking or some other
  56       // operation we don't care about
  57       return;
  58     }
  59     mAccumulatedBytes += aBytes;
  60   }
  61   double GetRateAtLastStop(bool* aReliable) const {
  62     double seconds = mAccumulatedTime.ToSeconds();
  63     *aReliable =
  64         (seconds >= 1.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
  65     if (seconds <= 0.0) return 0.0;
  66     return static_cast<double>(mAccumulatedBytes) / seconds;
  67   }
  68   double GetRate(bool* aReliable) const {
  69     TimeDuration time = mAccumulatedTime;
  70     if (mIsStarted) {
  71       time += TimeStamp::Now() - mLastStartTime;
  72     }
  73     double seconds = time.ToSeconds();
  74     *aReliable =
  75         (seconds >= 3.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
  76     if (seconds <= 0.0) return 0.0;
  77     return static_cast<double>(mAccumulatedBytes) / seconds;
  78   }
  79
  80  private:
  81   int64_t mAccumulatedBytes = 0;
  82   TimeDuration mAccumulatedTime;
  83   TimeStamp mLastStartTime;
  84   bool mIsStarted = false;
  85 };
  86
  87 }  // namespace mozilla
  88
  89 #endif  // MediaChannelStatistics_h_