Support both preconnection, and pre-resolution for subresources...

chrome/browser/net/referrer.h

 // Copyright (c) 2006-2010 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.
 
 // This class helps to remember what domains may be needed to be resolved when a
 // navigation takes place to a given URL.  This information is gathered when a
 // navigation to a subresource identifies a referring URL.
 // When future navigations take place to known referrer sites, then we
 // speculatively either pre-warm a TCP/IP conneciton, or at a minimum, resolve
 // the host name via DNS.
@@ skipping 20 matching lines @@
 // For each hostname in a Referrer, we have a ReferrerValue.  It indicates
 // exactly how much value (re: latency reduction, or connection use) has
 // resulted from having this entry.
 class ReferrerValue {
  public:
   ReferrerValue();
 
   // Used during deserialization.
   void SetSubresourceUseRate(double rate) { subresource_use_rate_ = rate; }
 
-  base::TimeDelta latency() const { return latency_; }
   base::Time birth_time() const { return birth_time_; }
-  void AccrueValue(const base::TimeDelta& delta) { latency_ += delta; }
 
-  // Record the fact that we navigated to the associated subresource URL.
+  // Record the fact that we navigated to the associated subresource URL.  This
+  // will increase the value of the expected subresource_use_rate_
   void SubresourceIsNeeded();
 
-  // Evaluate if it is worth making this preconnection, and return true if it
-  // seems worthwhile.  As a side effect, we also tally the proconnection for
-  // statistical purposes only.
-  bool IsPreconnectWorthDoing();
+  // Record the fact that the referrer of this subresource was observed. This
+  // will diminish the expected subresource_use_rate_ (and will only be
+  // counteracted later if we really needed this subresource as a consequence
+  // of our associated referrer.)
+  void ReferrerWasObserved();
 
   int64 navigation_count() const { return navigation_count_; }
-  int64 preconnection_count() const { return preconnection_count_; }
   double subresource_use_rate() const { return subresource_use_rate_; }
 
-  // Reduce the latency figure by a factor of 2, and return true if any latency
-  // remains.
+  int64 preconnection_count() const { return preconnection_count_; }
+  void IncrementPreconnectionCount() { ++preconnection_count_; }
+
+  int64 preresolution_count() const { return preresolution_count_; }
+  void preresolution_increment() { ++preresolution_count_; }
+
+  // Reduce the latency figure by a factor of 2, and return true if it still has
+  // subresources that could potentially be used.
   bool Trim();
 
  private:
-  base::TimeDelta latency_;  // Accumulated DNS resolution latency savings.
   const base::Time birth_time_;
 
   // The number of times this item was navigated to with the fixed referrer.
   int64 navigation_count_;
 
   // The number of times this item was preconnected as a consequence of its
   // referrer.
   int64 preconnection_count_;
 
-  // A smoothed estimate of the probability that a connection will be needed.
+  // The number of times this item was pre-resolved (via DNS) as a consequence
+  // of its referrer.
+  int64 preresolution_count_;
+
+  // A smoothed estimate of the expected number of connections that will be made
+  // to this subresource.
   double subresource_use_rate_;
 };
 
 //------------------------------------------------------------------------------
 // A list of domain names to pre-resolve. The names are the keys to this map,
 // and the values indicate the amount of benefit derived from having each name
 // around.
 typedef std::map<GURL, ReferrerValue> SubresourceMap;
 
 //------------------------------------------------------------------------------
 // There is one Referrer instance for each hostname that has acted as an HTTP
 // referer (note mispelling is intentional) for a hostname that was otherwise
 // unexpectedly navgated towards ("unexpected" in the sense that the hostname
 // was probably needed as a subresource of a page, and was not otherwise
 // predictable until the content with the reference arrived).  Most typically,
 // an outer page was a page fetched by the user, and this instance lists names
 // in SubresourceMap which are subresources and that were needed to complete the
 // rendering of the outer page.
 class Referrer : public SubresourceMap {
  public:
   Referrer() : use_count_(1) {}
   void IncrementUseCount() { ++use_count_; }
   int64 use_count() const { return use_count_; }
 
   // Add the indicated url to the list that are resolved via DNS when the user
   // navigates to this referrer.  Note that if the list is long, an entry may be
   // discarded to make room for this insertion.
   void SuggestHost(const GURL& url);
 
-  // Record additional usefulness of having this url in the list.
-  // Value is expressed as positive latency of amount delta.
-  void AccrueValue(const base::TimeDelta& delta,
-                   const GURL& url);
-
-  // Trim the Referrer, by first diminishing (scaling down) the latency for each
-  // ReferredValue.
-  // Returns true if there are any referring names with some latency left.
+  // Trim the Referrer, by first diminishing (scaling down) the subresource
+  // use expectation for each ReferredValue.
+  // Returns true if there are any referring names left.
   bool Trim();
 
   // Provide methods for persisting, and restoring contents into a Value class.
   Value* Serialize() const;
   void Deserialize(const Value& referrers);
 
   static void SetUsePreconnectValuations(bool dns) {
       use_preconnect_valuations_ = dns;
   }
 
@@ skipping 16 matching lines @@
 
   // We put these into a std::map<>, so we need copy constructors.
   // DISALLOW_COPY_AND_ASSIGN(Referrer);
   // TODO(jar): Consider optimization to use pointers to these instances, and
   // avoid deep copies during re-alloc of the containing map.
 };
 
 }  // namespace chrome_browser_net
 
 #endif  // CHROME_BROWSER_NET_REFERRER_H_