Add in-memory caching of network quality estimates across network changes.

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 <map>
+#include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
+#include "base/memory/scoped_ptr.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"
 #include "net/base/network_quality.h"
 
 namespace net {
 
 // NetworkQualityEstimator provides network quality estimates (quality of the
 // full paths to all origins that have been connected to).
@@ skipping 31 matching lines @@
   // Notifies NetworkQualityEstimator that a response has been received.
   // |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 cumulative_prefilter_bytes_read,
                           int64_t prefiltered_bytes_read);
 
+ protected:
+  // NetworkID is used to uniquely identify a network.
+  // For the purpose of network quality estimation and caching, a network is
+  // uniquely identified by a combination of |type| and
+  // |id|. This approach is unable to distinguish networks with
+  // same name (e.g., different Wi-Fi networks with same SSID).
+  // This is a protected member to expose it to tests.
+  struct NET_EXPORT_PRIVATE NetworkID {
+    NetworkID(NetworkChangeNotifier::ConnectionType type, const std::string& id)
+        : type(type), id(id) {}
+    NetworkID(const NetworkID& other) : type(other.type), id(other.id) {}
+    ~NetworkID() {}
+
+    NetworkID& operator=(const NetworkID& other) {
+      type = other.type;
+      id = other.id;
+      return *this;
+    }
+
+    // Overloaded because NetworkID is used as key in a map.
+    bool operator<(const NetworkID& other) const {
+      return type < other.type || (type == other.type && id < other.id);
+    }
+
+    // Connection type of the network.
+    NetworkChangeNotifier::ConnectionType type;
+
+    // Name of this network. This is set to:
+    // - Wi-Fi SSID if the device is connected to a Wi-Fi access point and the
+    //   SSID name is available, or
+    // - MCC/MNC code of the cellular carrier if the device is connected to a
+    //   cellular network, or
+    // - "Ethernet" in case the device is connected to ethernet.
+    // - An empty string in all other cases or if the network name is not
+    //   exposed by platform APIs.
+    std::string id;
+  };
+
+  // Construct a NetworkQualityEstimator instance allowing for test
+  // configuration. Registers for network type change notifications so estimates
+  // can be kept network specific.
+  // |variation_params| is the map containing all field trial parameters for the
+  // network quality estimator field trial.
+  // |allow_local_host_requests_for_tests| should only be true when testing
+  // against local HTTP server and allows the requests to local host to be
+  // used for network quality estimation.
+  // |allow_smaller_responses_for_tests| should only be true when testing.
+  // Allows the responses smaller than |kMinTransferSizeInBytes| or shorter than
+  // |kMinRequestDurationMicroseconds| to be used for network quality
+  // estimation.
+  NetworkQualityEstimator(
+      const std::map<std::string, std::string>& variation_params,
+      bool allow_local_host_requests_for_tests,
+      bool allow_smaller_responses_for_tests);
+
+  // Returns true if the cached network quality estimate was successfully read.
+  bool ReadCachedNetworkQualityEstimate();
+
+  // NetworkChangeNotifier::ConnectionTypeObserver implementation.
+  void OnConnectionTypeChanged(
+      NetworkChangeNotifier::ConnectionType type) override;
+
  private:
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, StoreObservations);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestKbpsRTTUpdates);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestAddObservation);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, ObtainOperatingParams);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, HalfLifeParam);
   FRIEND_TEST_ALL_PREFIXES(URLRequestTestHTTP, NetworkQualityEstimator);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            PercentileSameTimestamps);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            PercentileDifferentTimestamps);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, ComputedPercentiles);
+  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestCaching);
+  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
+                           TestLRUCacheMaximumSize);
+
+  // CachedNetworkQuality stores the quality of a previously seen network.
+  class NET_EXPORT_PRIVATE CachedNetworkQuality {
+   public:
+    explicit CachedNetworkQuality(const NetworkQuality& network_quality);
+    CachedNetworkQuality(const CachedNetworkQuality& other);
+    ~CachedNetworkQuality();
+
+    // Returns the network quality associated with this cached entry.
+    const NetworkQuality network_quality() const { return network_quality_; }
+
+    // Returns true if this cache entry was updated before
+    // |cached_network_quality|.
+    bool OlderThan(const CachedNetworkQuality& cached_network_quality) const;
+
+    // Time when this cache entry was last updated.
+    const base::TimeTicks last_update_time_;
+
+    // Quality of this cached network.
+    const NetworkQuality network_quality_;
+
+   private:
+    DISALLOW_ASSIGN(CachedNetworkQuality);
+  };
 
   // Records the round trip time or throughput observation, along with the time
   // the observation was made.
   struct NET_EXPORT_PRIVATE 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;
   };
 
   // Holds an observation and its weight.
-  struct WeightedObservation {
+  struct NET_EXPORT_PRIVATE WeightedObservation {
     WeightedObservation(int32_t value, double weight)
         : value(value), weight(weight) {}
     WeightedObservation(const WeightedObservation& other)
         : WeightedObservation(other.value, other.weight) {}
 
     WeightedObservation& operator=(const WeightedObservation& other) {
       value = other.value;
       weight = other.weight;
       return *this;
     }
 
     // Required for sorting the samples in the ascending order of values.
     bool operator<(const WeightedObservation& other) const {
       return (value < other.value);
     }
 
     // Value of the sample.
     int32_t value;
 
     // Weight of the sample. This is computed based on how much time has passed
     // since the sample was taken.
     double weight;
   };
 
   // Stores observations sorted by time.
   class NET_EXPORT_PRIVATE ObservationBuffer {
    public:
     explicit ObservationBuffer(double weight_multiplier_per_second);
-
     ~ObservationBuffer();
 
     // Adds |observation| to the buffer. The oldest observation in the buffer
     // will be evicted to make room if the buffer is already full.
     void AddObservation(const Observation& observation);
 
     // Returns the number of observations in this buffer.
     size_t Size() const;
 
     // Clears the observations stored in this buffer.
@@ skipping 23 matching lines @@
     // The factor by which the weight of an observation reduces every second.
     // For example, if an observation is 6 seconds old, its weight would be:
     //     weight_multiplier_per_second_ ^ 6
     // Calculated from |kHalfLifeSeconds| by solving the following equation:
     //     weight_multiplier_per_second_ ^ kHalfLifeSeconds = 0.5
     const double weight_multiplier_per_second_;
 
     DISALLOW_COPY_AND_ASSIGN(ObservationBuffer);
   };
 
+  // This does not use a unordered_map or hash_map for code simplicity (key just
+  // implements operator<, rather than hash and equality) and because the map is
+  // tiny.
+  typedef std::map<NetworkID, CachedNetworkQuality> CachedNetworkQualities;
+
   // 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;
 
   // Minimum valid value of the variation parameter that holds RTT (in
   // milliseconds) values.
   static const int kMinimumRTTVariationParameterMsec = 1;
 
   // Minimum valid value of the variation parameter that holds throughput (in
   // kbps) values.
   static const int kMinimumThroughputVariationParameterKbps = 1;
 
-  // Construct a NetworkQualityEstimator instance allowing for test
-  // configuration. Registers for network type change notifications so estimates
-  // can be kept network specific.
-  // |variation_params| is the map containing all field trial parameters for the
-  // network quality estimator field trial.
-  // |allow_local_host_requests_for_tests| should only be true when testing
-  // against local HTTP server and allows the requests to local host to be
-  // used for network quality estimation.
-  // |allow_smaller_responses_for_tests| should only be true when testing
-  // against local HTTP server and allows the responses smaller than
-  // |kMinTransferSizeInBytes| or shorter than |kMinRequestDurationMicroseconds|
-  // to be used for network quality estimation.
-  NetworkQualityEstimator(
-      const std::map<std::string, std::string>& variation_params,
-      bool allow_local_host_requests_for_tests,
-      bool allow_smaller_responses_for_tests);
+  // Maximum size of the cache that holds network quality estimates.
+  // Smaller size may reduce the cache hit rate due to frequent evictions.
+  // Larger size may affect performance.
+  static const size_t kMaximumNetworkQualityCacheSize = 10;
+
+  // Maximum number of observations that can be held in the ObservationBuffer.
+  static const size_t kMaximumObservationsBufferSize = 300;
 
   // Obtains operating parameters from the field trial parameters.
   void ObtainOperatingParams(
       const std::map<std::string, std::string>& variation_params);
 
   // Adds the default median RTT and downstream throughput estimate for the
   // current connection type to the observation buffer.
   void AddDefaultEstimates();
 
-  // Returns the maximum size of the observation buffer.
-  // Used for testing.
-  size_t GetMaximumObservationBufferSizeForTests() const;
-
-  // Returns true if the size of all observation buffers is equal to the
-  // |expected_size|. Used for testing.
-  bool VerifyBufferSizeForTests(size_t expected_size) const;
-
-  // NetworkChangeNotifier::ConnectionTypeObserver implementation.
-  void OnConnectionTypeChanged(
-      NetworkChangeNotifier::ConnectionType type) override;
-
   // Returns an estimate of network quality at the specified |percentile|.
   // |percentile| must be between 0 and 100 (both inclusive) with higher
   // percentiles indicating less performant networks. For example, if
   // |percentile| is 90, then the network is expected to be faster than the
   // returned estimate with 0.9 probability. Similarly, network is expected to
   // be slower than the returned estimate with 0.1 probability.
   NetworkQuality GetEstimate(int percentile) const;
 
+  // Returns the current network ID checking by calling the platform APIs.
+  // Virtualized for testing.
+  virtual NetworkID GetCurrentNetworkID() const;
+
+  // Writes the estimated quality of the current network to the cache.
+  void CacheNetworkQualityEstimate();
+
   // Records the UMA related to RTT.
   void RecordRTTUMA(int32_t estimated_value_msec,
                     int32_t actual_value_msec) const;
 
   // Determines if the requests to local host can be used in estimating the
   // network quality. Set to true only for tests.
   const bool allow_localhost_requests_;
 
   // Determines if the responses smaller than |kMinTransferSizeInBytes|
   // or shorter than |kMinTransferSizeInBytes| can be used in estimating the
   // network quality. Set to true only for tests.
   const bool allow_small_responses_;
 
   // 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_;
+  // ID of the current network.
+  NetworkID current_network_id_;
 
-  // 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_;
+  // Peak network quality (fastest round-trip-time (RTT) and highest
+  // downstream throughput) measured since last connectivity change. RTT is
+  // measured from time the request is sent until the first byte received.
+  // The accuracy is decreased by ignoring these factors:
+  // 1) Multiple URLRequests can occur concurrently.
+  // 2) Includes server processing time.
+  NetworkQuality peak_network_quality_;
 
-  // 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.
-  int32_t peak_kbps_since_last_connection_change_;
+  // Cache that stores quality of previously seen networks.
+  CachedNetworkQualities cached_network_qualities_;
 
   // Buffer that holds Kbps observations sorted by timestamp.
   ObservationBuffer kbps_observations_;
 
   // Buffer that holds RTT (in milliseconds) observations sorted by timestamp.
   ObservationBuffer rtt_msec_observations_;
 
   // Default network quality observations obtained from the network quality
   // estimator field trial parameters. The observations are indexed by
   // ConnectionType.
   NetworkQuality
       default_observations_[NetworkChangeNotifier::CONNECTION_LAST + 1];
 
   // Estimated network quality. Updated on mainframe requests.
   NetworkQuality estimated_median_network_quality_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_