Store network quality samples so we can compute percentiles.

net/base/network_quality_estimator.h

 // Copyright 2015 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.
 
 #ifndef NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_
 #define NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_
 
 #include <stdint.h>
 
+#include <deque>
+
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
 
 struct NetworkQuality;
 
 // NetworkQualityEstimator provides network quality estimates (quality of the
 // full paths to all origins that have been connected to).
 // The estimates are based on the observed organic traffic.
 // A NetworkQualityEstimator instance is attached to URLRequestContexts and
 // observes the traffic of URLRequests spawned from the URLRequestContexts.
 // A single instance of NQE can be attached to multiple URLRequestContexts,
 // thereby increasing the single NQE instance's accuracy by providing more
 // observed traffic characteristics.
 class NET_EXPORT_PRIVATE NetworkQualityEstimator
     : public NetworkChangeNotifier::ConnectionTypeObserver {
  public:
   // Creates a new NetworkQualityEstimator.
   NetworkQualityEstimator();
 
   ~NetworkQualityEstimator() override;
 
-  // Returns an estimate of the current network quality.
-  NetworkQuality GetEstimate() const;
+  // Returns the peak estimates (fastest RTT and peak throughput) of the
+  // current network.
+  NetworkQuality GetPeakEstimate() const;
 
   // Notifies NetworkQualityEstimator that a response has been received.
-  // |prefilter_bytes_read| is the count of the bytes received prior to
-  // applying filters (e.g. decompression, SDCH) from request creation time
+  // |cummulative_prefilter_bytes_read| is the count of the bytes received prior
+  // to applying filters (e.g. decompression, SDCH) from request creation time
   // until now.
+  // |prefiltered_bytes_read| is the count of the bytes received prior
+  // to applying filters in the most recent read.
   void NotifyDataReceived(const URLRequest& request,
-                          int64_t prefilter_bytes_read);
+                          int64_t cummulative_prefilter_bytes_read,
+                          int64_t prefiltered_bytes_read);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            TestPeakKbpsFastestRTTUpdates);
   FRIEND_TEST_ALL_PREFIXES(URLRequestTestHTTP, NetworkQualityEstimator);
 
+  // Sample is used to store RTT and Kbps samples in buffers. A sample has a
+  // value and a timestamp (when the sample was taken).
+  class Sample {
+   public:
+    explicit Sample(int value);

[mmenke, 2015/06/03 18:31:40]

Suggest taking the time here, to make things a but more explicit.  Also remember
someone saying something about possibly loading state from disk.

[tbansal1, 2015/06/05 01:50:08]

Done.

+
+    virtual ~Sample();

[mmenke, 2015/06/03 18:31:39]

--virtual

[tbansal1, 2015/06/05 01:50:08]

Done.

+
+    // Value of the sample.
+    const int value_;

[mmenke, 2015/06/03 18:31:39]

Classes aren't allowed to have public member variables.  This should either be a
struct, or these should be private with public accessors.

Since they're in an stl container, and you need them to be copiable, I'd go with
structs.

[tbansal1, 2015/06/05 01:50:08]

Done.

+
+    // Time when the sample was taken.
+    const base::TimeTicks timestamp_;
+  };
+
+  // Ring Buffer is used to store samples sorted by time.
+  class RingBuffer {

[mmenke, 2015/06/03 18:31:39]

Think it's more important to name classes after what they contain, rather than
the data format they use to do it, which is more of an internal implementation
detail.

Maybe just SampleBuffer, SampleCache, SampleSet, or even SampleRingBuffer, if
you really think that's important.

[tbansal1, 2015/06/05 01:50:08]

Done.

[bengr, 2015/06/05 20:44:13]

I like SampleBuffer better. Also, can we use the word "Observation" instead of
"Sample" everywhere?

[tbansal1, 2015/06/08 20:27:51]

Done.

+   public:
+    RingBuffer();
+
+    virtual ~RingBuffer();

[mmenke, 2015/06/03 18:31:39]

--virtual

[tbansal1, 2015/06/05 01:50:08]

Done.

+
+    void AddSample(int value);
+
+   private:
+    // Maximum number of samples to hold in the RingBuffer.
+    const uint32_t kMaximumSamples = 300;

[mmenke, 2015/06/03 18:31:40]

static?

[tbansal1, 2015/06/05 01:50:08]

Done.

+
+    // Buffer that holds samples sorted by time.
+    // Oldest sample is at the front of the queue.
+    std::deque<Sample> samples_;
+  };
+
   // Tiny transfer sizes may give inaccurate throughput results.
   // Minimum size of the transfer over which the throughput is computed.
   static const int kMinTransferSizeInBytes = 10000;
 
   // Minimum duration (in microseconds) of the transfer over which the
   // throughput is computed.
   static const int kMinRequestDurationMicroseconds = 1000;
 
   // Construct a NetworkQualityEstimator instance allowing for test
   // configuration.
@@ skipping 25 matching lines @@
   // Fastest round-trip-time (RTT) since last connectivity change. RTT measured
   // from URLRequest creation until first byte received.
   base::TimeDelta fastest_RTT_since_last_connection_change_;
 
   // Rough measurement of downlink peak Kbps witnessed since last connectivity
   // change. The accuracy is decreased by ignoring these factors:
   // 1) Multiple URLRequests can occur concurrently.
   // 2) The transfer time includes at least one RTT while no bytes are read.
   uint64_t peak_kbps_since_last_connection_change_;
 
+  // Buffer that holds Kbps samples.
+  RingBuffer kbps_;

[mmenke, 2015/06/03 18:31:39]

Maybe kbps_samples_, and same for the next one?

[tbansal1, 2015/06/05 01:50:08]

Done.

+
+  // Buffer that holds RTT (in milliseconds) samples.
+  RingBuffer rtt_msec_;
+
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_