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

net/base/network_quality_estimator.cc

Index: net/base/network_quality_estimator.cc
diff --git a/net/base/network_quality_estimator.cc b/net/base/network_quality_estimator.cc
index 6415ee6e6d7eb36b47ab4fd568d3537283b27729..e7330de6fadeae8e9a3a9a931d696ef88de1a6ab 100644
--- a/net/base/network_quality_estimator.cc
+++ b/net/base/network_quality_estimator.cc
@@ -4,17 +4,23 @@
 
 #include "net/base/network_quality_estimator.h"
 
-#include <string>
-
 #include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
+#include "build/build_config.h"
 #include "net/base/net_util.h"
-#include "net/base/network_quality.h"
+#include "net/base/network_interfaces.h"
 #include "net/url_request/url_request.h"
 #include "url/gurl.h"
 
+#if defined(OS_ANDROID)
+#include "net/android/network_library.h"
+#endif  // OS_ANDROID
+
 namespace net {
 
+const uint32_t NetworkQualityEstimator::kMaximumNetworkQualityCacheSize = 10;
+
 NetworkQualityEstimator::NetworkQualityEstimator()
     : NetworkQualityEstimator(false) {
 }
@@ -23,12 +29,16 @@ NetworkQualityEstimator::NetworkQualityEstimator(
     bool allow_local_host_requests_for_tests)
     : allow_localhost_requests_(allow_local_host_requests_for_tests),
       last_connection_change_(base::TimeTicks::Now()),
-      current_connection_type_(NetworkChangeNotifier::GetConnectionType()),
       bytes_read_since_last_connection_change_(false),
-      peak_kbps_since_last_connection_change_(0) {
+      peak_kbps_since_last_connection_change_(0),
+      current_network_id_(NetworkID(NetworkChangeNotifier::GetConnectionType(),
+                                    std::string())) {
   static_assert(kMinRequestDurationMicroseconds > 0,
                 "Minimum request duration must be > 0");
+  static_assert(kMaximumNetworkQualityCacheSize > 0,
+                "Size of the network quality cache must be > 0");
   NetworkChangeNotifier::AddConnectionTypeObserver(this);
+  current_network_id_.id = GetCurrentNetworkName();
 }
 
 NetworkQualityEstimator::~NetworkQualityEstimator() {
@@ -77,7 +87,7 @@ void NetworkQualityEstimator::OnConnectionTypeChanged(
     NetworkChangeNotifier::ConnectionType type) {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (bytes_read_since_last_connection_change_) {
-    switch (current_connection_type_) {
+    switch (current_network_id_.type) {
       case NetworkChangeNotifier::CONNECTION_UNKNOWN:
         UMA_HISTOGRAM_TIMES("NQE.FastestRTT.Unknown",
                             fastest_RTT_since_last_connection_change_);
@@ -111,13 +121,14 @@ void NetworkQualityEstimator::OnConnectionTypeChanged(
                             fastest_RTT_since_last_connection_change_);
         break;
       default:
-        NOTREACHED();
+        NOTREACHED() << "Unexpected connection type = "
+                     << current_network_id_.type;
         break;
     }
   }
 
   if (peak_kbps_since_last_connection_change_) {
-    switch (current_connection_type_) {
+    switch (current_network_id_.type) {
       case NetworkChangeNotifier::CONNECTION_UNKNOWN:
         UMA_HISTOGRAM_COUNTS("NQE.PeakKbps.Unknown",
                              peak_kbps_since_last_connection_change_);
@@ -151,15 +162,28 @@ void NetworkQualityEstimator::OnConnectionTypeChanged(
                              peak_kbps_since_last_connection_change_);
         break;
       default:
-        NOTREACHED();
+        NOTREACHED() << "Unexpected connection type = "
+                     << current_network_id_.type;
         break;
     }
   }
 
+  // Write the estimates of the previous network to the cache.
+  CacheNetworkQualityEstimate();
+
   last_connection_change_ = base::TimeTicks::Now();
   bytes_read_since_last_connection_change_ = false;
   peak_kbps_since_last_connection_change_ = 0;
-  current_connection_type_ = type;
+  fastest_RTT_since_last_connection_change_ = base::TimeDelta();
+  current_network_id_.type = type;
+  current_network_id_.id = GetCurrentNetworkName();
+
+  // Read any cached estimates for the new network.
+  ReadCachedNetworkQualityEstimate();
+}
+
+size_t NetworkQualityEstimator::GetCacheSizeForTests() const {
+  return cached_network_quality_.size();
 }
 
 NetworkQuality NetworkQualityEstimator::GetEstimate() const {
@@ -177,4 +201,121 @@ NetworkQuality NetworkQualityEstimator::GetEstimate() const {
                         peak_kbps_since_last_connection_change_, 0.1);
 }
 
+std::string NetworkQualityEstimator::GetCurrentNetworkName() const {
+  // TODO(tbansal): crbug.com/498068 Add NetworkQualityEstimatorAndroid class
+  // that overrides this method on the Android platform.
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  switch (current_network_id_.type) {
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_UNKNOWN:
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_NONE:
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_BLUETOOTH:
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_ETHERNET:
+      return std::string();
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_WIFI:
+#if defined(OS_ANDROID) || defined(OS_LINUX) || defined(OS_CHROMEOS)
+      return GetWifiSSID();
+#else
+      return std::string();
+#endif
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_2G:
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_3G:
+    case NetworkChangeNotifier::ConnectionType::CONNECTION_4G:
+#if defined(OS_ANDROID)
+      return android::GetTelephonyNetworkOperator();
+#else
+      return std::string();
+#endif
+    default:
+      NOTREACHED() << "Unexpected connection type = "
+                   << current_network_id_.type;
+      return std::string();
+  }
+}
+
+bool NetworkQualityEstimator::ReadCachedNetworkQualityEstimate() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  CachedNetworkQualities::iterator it =
+      cached_network_quality_.find(current_network_id_);
+  if (it != cached_network_quality_.end()) {
+    // TOOD(tbansal): Populate these values back into the median computing
+    // algorithm.
+    // Add UMA to record how frequently matches happen.
+    // Ensure that the estimates read are non-zero before populating them into
+    // the median computing algorithm.
+    peak_kbps_since_last_connection_change_ =
+        it->second->GetNetworkQuality().peak_throughput_kbps;
+    fastest_RTT_since_last_connection_change_ =
+        it->second->GetNetworkQuality().fastest_rtt;
+    return true;
+  }
+  return false;
+}
+
+void NetworkQualityEstimator::CacheNetworkQualityEstimate() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_LE(cached_network_quality_.size(), kMaximumNetworkQualityCacheSize);
+
+  // TODO(tbansal): The following variables should be initialized using the
+  // median values reported by the NetworkQualityEstimator.
+  int median_kbps = peak_kbps_since_last_connection_change_;
+  base::TimeDelta median_rtt = fastest_RTT_since_last_connection_change_;
+
+  // If this network is already in the cache, overwrite that entry.
+  CachedNetworkQualities::iterator it =
+      cached_network_quality_.find(current_network_id_);
+  if (it != cached_network_quality_.end()) {
+    (it->second)->UpdateNetworkQuality(median_kbps, median_rtt);
+    return;
+  }
+
+  if (cached_network_quality_.size() == kMaximumNetworkQualityCacheSize) {
+    // Remove the oldest entry.
+    CachedNetworkQualities::iterator oldest_entry_iterator =
+        cached_network_quality_.begin();
+
+    for (CachedNetworkQualities::iterator iterator =
+             cached_network_quality_.begin();
+         iterator != cached_network_quality_.end(); ++iterator) {
+      if ((oldest_entry_iterator->second)->last_update_time() >
+          (iterator->second)->last_update_time()) {
+        oldest_entry_iterator = iterator;
+      }
+    }
+    cached_network_quality_.erase(oldest_entry_iterator);
+  }
+
+  DCHECK_LT(cached_network_quality_.size(), kMaximumNetworkQualityCacheSize);
+  cached_network_quality_.insert(
+      std::make_pair(current_network_id_,
+                     make_scoped_ptr(new CachedNetworkQuality(
+                         NetworkQuality(median_rtt, 0.0, median_kbps, 0.0)))));
+  DCHECK_LE(cached_network_quality_.size(), kMaximumNetworkQualityCacheSize);
+}
+
+NetworkQualityEstimator::CachedNetworkQuality::CachedNetworkQuality(
+    const NetworkQuality& network_quality)
+    : last_update_time_(base::TimeTicks::Now()),
+      network_quality_(network_quality) {
+}
+
+NetworkQualityEstimator::CachedNetworkQuality::~CachedNetworkQuality() {
+}
+
+void NetworkQualityEstimator::CachedNetworkQuality::UpdateNetworkQuality(
+    uint64_t median_kbps,
+    const base::TimeDelta& median_rtt) {
+  DCHECK_GE(median_kbps, 0U);
+  DCHECK_GE(median_rtt, base::TimeDelta());
+  last_update_time_ = base::TimeTicks::Now();
+
+  network_quality_ = NetworkQuality(median_rtt, 0.0, median_kbps, 0.0);
+}
+
+const NetworkQuality
+NetworkQualityEstimator::CachedNetworkQuality::GetNetworkQuality() const {
+  return network_quality_;
+}
+
 }  // namespace net