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-rw-r--r--dom/media/MediaChannelStatistics.h89
1 files changed, 89 insertions, 0 deletions
diff --git a/dom/media/MediaChannelStatistics.h b/dom/media/MediaChannelStatistics.h
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+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#if !defined(MediaChannelStatistics_h_)
+# define MediaChannelStatistics_h_
+
+# include "mozilla/TimeStamp.h"
+
+namespace mozilla {
+
+// Number of bytes we have accumulated before we assume the connection download
+// rate can be reliably calculated. 57 Segments at IW=3 allows slow start to
+// reach a CWND of 30 (See bug 831998)
+static const int64_t RELIABLE_DATA_THRESHOLD = 57 * 1460;
+
+/**
+ * This class is useful for estimating rates of data passing through
+ * some channel. The idea is that activity on the channel "starts"
+ * and "stops" over time. At certain times data passes through the
+ * channel (usually while the channel is active; data passing through
+ * an inactive channel is ignored). The GetRate() function computes
+ * an estimate of the "current rate" of the channel, which is some
+ * kind of average of the data passing through over the time the
+ * channel is active.
+ *
+ * All methods take "now" as a parameter so the user of this class can
+ * control the timeline used.
+ */
+class MediaChannelStatistics {
+ public:
+ MediaChannelStatistics() = default;
+ MediaChannelStatistics(const MediaChannelStatistics&) = default;
+ MediaChannelStatistics& operator=(const MediaChannelStatistics&) = default;
+
+ void Reset() {
+ mLastStartTime = TimeStamp();
+ mAccumulatedTime = TimeDuration(0);
+ mAccumulatedBytes = 0;
+ mIsStarted = false;
+ }
+ void Start() {
+ if (mIsStarted) return;
+ mLastStartTime = TimeStamp::Now();
+ mIsStarted = true;
+ }
+ void Stop() {
+ if (!mIsStarted) return;
+ mAccumulatedTime += TimeStamp::Now() - mLastStartTime;
+ mIsStarted = false;
+ }
+ void AddBytes(int64_t aBytes) {
+ if (!mIsStarted) {
+ // ignore this data, it may be related to seeking or some other
+ // operation we don't care about
+ return;
+ }
+ mAccumulatedBytes += aBytes;
+ }
+ double GetRateAtLastStop(bool* aReliable) const {
+ double seconds = mAccumulatedTime.ToSeconds();
+ *aReliable =
+ (seconds >= 1.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
+ if (seconds <= 0.0) return 0.0;
+ return static_cast<double>(mAccumulatedBytes) / seconds;
+ }
+ double GetRate(bool* aReliable) const {
+ TimeDuration time = mAccumulatedTime;
+ if (mIsStarted) {
+ time += TimeStamp::Now() - mLastStartTime;
+ }
+ double seconds = time.ToSeconds();
+ *aReliable =
+ (seconds >= 3.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
+ if (seconds <= 0.0) return 0.0;
+ return static_cast<double>(mAccumulatedBytes) / seconds;
+ }
+
+ private:
+ int64_t mAccumulatedBytes = 0;
+ TimeDuration mAccumulatedTime;
+ TimeStamp mLastStartTime;
+ bool mIsStarted = false;
+};
+
+} // namespace mozilla
+
+#endif // MediaChannelStatistics_h_