зеркало из https://github.com/mozilla/gecko-dev.git
95 строки
2.9 KiB
C++
95 строки
2.9 KiB
C++
/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#if !defined(MediaChannelStatistics_h_)
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#define MediaChannelStatistics_h_
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#include "mozilla/TimeStamp.h"
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namespace mozilla {
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// Number of bytes we have accumulated before we assume the connection download
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// rate can be reliably calculated. 57 Segments at IW=3 allows slow start to
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// reach a CWND of 30 (See bug 831998)
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static const int64_t RELIABLE_DATA_THRESHOLD = 57 * 1460;
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/**
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* This class is useful for estimating rates of data passing through
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* some channel. The idea is that activity on the channel "starts"
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* and "stops" over time. At certain times data passes through the
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* channel (usually while the channel is active; data passing through
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* an inactive channel is ignored). The GetRate() function computes
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* an estimate of the "current rate" of the channel, which is some
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* kind of average of the data passing through over the time the
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* channel is active.
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*
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* All methods take "now" as a parameter so the user of this class can
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* control the timeline used.
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*/
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class MediaChannelStatistics {
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public:
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MediaChannelStatistics() = default;
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MediaChannelStatistics(const MediaChannelStatistics&) = default;
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MediaChannelStatistics& operator=(const MediaChannelStatistics&) = default;
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void Reset() {
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mLastStartTime = TimeStamp();
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mAccumulatedTime = TimeDuration(0);
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mAccumulatedBytes = 0;
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mIsStarted = false;
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}
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void Start() {
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if (mIsStarted)
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return;
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mLastStartTime = TimeStamp::Now();
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mIsStarted = true;
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}
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void Stop() {
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if (!mIsStarted)
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return;
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mAccumulatedTime += TimeStamp::Now() - mLastStartTime;
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mIsStarted = false;
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}
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void AddBytes(int64_t aBytes) {
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if (!mIsStarted) {
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// ignore this data, it may be related to seeking or some other
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// operation we don't care about
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return;
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}
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mAccumulatedBytes += aBytes;
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}
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double GetRateAtLastStop(bool* aReliable) const
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{
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double seconds = mAccumulatedTime.ToSeconds();
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*aReliable = (seconds >= 1.0) ||
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(mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
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if (seconds <= 0.0)
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return 0.0;
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return static_cast<double>(mAccumulatedBytes)/seconds;
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}
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double GetRate(bool* aReliable) const
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{
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TimeDuration time = mAccumulatedTime;
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if (mIsStarted) {
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time += TimeStamp::Now() - mLastStartTime;
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}
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double seconds = time.ToSeconds();
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*aReliable = (seconds >= 3.0) ||
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(mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
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if (seconds <= 0.0)
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return 0.0;
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return static_cast<double>(mAccumulatedBytes)/seconds;
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}
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private:
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int64_t mAccumulatedBytes = 0;
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TimeDuration mAccumulatedTime;
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TimeStamp mLastStartTime;
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bool mIsStarted = false;
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};
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} // namespace mozilla
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#endif // MediaChannelStatistics_h_
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