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/net_export.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
 
-struct NetworkQuality;
+class 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
+  // |cumulative_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 cumulative_prefilter_bytes_read,
+                          int64_t prefiltered_bytes_read);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, StoreObservations);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            TestPeakKbpsFastestRTTUpdates);
+  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestAddObservation);
   FRIEND_TEST_ALL_PREFIXES(URLRequestTestHTTP, NetworkQualityEstimator);
 
+  // Observation is used to store RTT and Kbps observation in buffers. An
+  // observation has a value and a timestamp (when the observation was taken).
+  struct Observation {
+    Observation(int32_t value, base::TimeTicks timestamp);
+
+    ~Observation();
+
+    // Value of the observation.
+    const int32_t value;
+
+    // Time when the observation was taken.
+    const base::TimeTicks timestamp;
+  };
+
+  // ObservationBuffer is used to store observations sorted by time.
+  class ObservationBuffer {
+   public:
+    ObservationBuffer();
+
+    ~ObservationBuffer();
+
+    // Adds an observation to the buffer. The oldest observation in the buffer
+    // will be popped out and discarded if the buffer is already full.
+    void AddObservation(int32_t value);
+
+    // Returns the number of observations in this buffer.
+    size_t size() const;
+
+   private:
+    // Maximum number of observations to hold in the ObservationBuffer.
+    static const size_t kMaximumObservations;

[bengr, 2015/06/09 20:46:33]

Why not just put this in an anonymous namespace in the .cc?

[tbansal1, 2015/06/10 01:00:05]

Now, this is exposed to tests. I believe in that case, putting 
in .h is a better design than putting in anonymous namespace
and then exposing it.

+
+    // Buffer that holds observations sorted by time.

[bengr, 2015/06/09 20:46:33]

Perhaps rewrite as:

Holds observations sorted by time, with the oldest observation at the front of
the queue.

[tbansal1, 2015/06/10 01:00:05]

Done.

+    // Oldest observation is at the front of the queue.
+    std::deque<Observation> observations_;
+
+    DISALLOW_COPY_AND_ASSIGN(ObservationBuffer);
+  };
+
   // 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 13 matching lines @@
   const bool allow_localhost_requests_;
 
   // Time when last connection change was observed.
   base::TimeTicks last_connection_change_;
 
   // Last value passed to |OnConnectionTypeChanged|. This indicates the
   // current connection type.
   NetworkChangeNotifier::ConnectionType current_connection_type_;
 
   // Set if any network data has been received since last connectivity change.
-  bool bytes_read_since_last_connection_change_;
+  bool have_received_bytes_since_last_connection_change_;
 
   // 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
+  // Rough measurement of downstream 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_;
+  int32_t peak_kbps_since_last_connection_change_;
+
+  // Buffer that holds Kbps observations.
+  ObservationBuffer kbps_observations_;
+
+  // Buffer that holds RTT (in milliseconds) observations.
+  ObservationBuffer rtt_msec_observations_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_