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      1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // A RendererNetPredictor instance is maintained for each RenderThread.
      6 // URL strings are typically added to the embedded queue during rendering.
      7 // The first addition to the queue (transitioning from empty to having
      8 // some names) causes a processing task to be added to the Renderer Thread.
      9 // The processing task gathers all buffered names, and send them via IPC
     10 // to the browser, so that DNS lookups can be performed before the user attempts
     11 // to traverse a link.
     12 // This class removed some duplicates, and discards numeric IP addresss
     13 // (which wouldn't looked up in DNS anyway).
     14 // To limit the time during the processing task (and avoid stalling the Render
     15 // thread), several limits are placed on how much of the queue to process.
     16 // If the processing task is not able to completely empty the queue, it
     17 // schedules a future continuation of the task, and keeps the map of already
     18 // sent names.  If the entire queue is processed, then the list of "sent names"
     19 // is cleared so that future gatherings might again pass along the same names.
     20 
     21 #ifndef CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_
     22 #define CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_
     23 
     24 #include <map>
     25 #include <string>
     26 
     27 #include "base/basictypes.h"
     28 #include "base/memory/weak_ptr.h"
     29 #include "chrome/renderer/net/predictor_queue.h"
     30 
     31 class RendererNetPredictor {
     32  public:
     33   RendererNetPredictor();
     34   ~RendererNetPredictor();
     35 
     36   // Push a name into the queue to be resolved.
     37   void Resolve(const char* name, size_t length);
     38 
     39   // SubmitHosts processes the buffered names, and submits them for DNS
     40   // prefetching.
     41   // Note that browser process may decide which names should be looked up (to
     42   // pre-warm the cache) based on what has been (or not been) looked up
     43   // recently.
     44   // If sending for DNS lookup is incomplete (queue is not empty, or not all
     45   // names in map are sent, or ...) then a task to continue processing is
     46   // sent to our thread loop.
     47   void SubmitHostnames();
     48 
     49   // The following is private, but exposed for testing purposes only.
     50   static bool is_numeric_ip(const char* name, size_t length);
     51 
     52  private:
     53   // ExtractBufferedNames pulls names from queue into the map, reducing or
     54   // eliminating a waiting queue.
     55   // The size_goal argument can be used to reduce the amount of
     56   // processing done in this method, and can leave some data
     57   // in the buffer under some circumstances.
     58   // If size_goal is zero, then extraction proceeds until
     59   // the queue is empty.  If size goal is positive, then
     60   // extraction continues until the domain_map_ contains
     61   // at least the specified number of names, or the buffer is empty.
     62   void ExtractBufferedNames(size_t size_goal = 0);
     63 
     64   // DnsPrefetchNames does not check the buffer, and just sends names
     65   // that are already collected in the domain_map_ for DNS lookup.
     66   // If max_count is zero, then all available names are sent; and
     67   // if positive, then at most max_count names will be sent.
     68   void DnsPrefetchNames(size_t max_count = 0);
     69 
     70   // Reset() restores initial state provided after construction.
     71   // This discards ALL queue entries, and map entries.
     72   void Reset();
     73 
     74   // We use c_string_queue_ to hold lists of names supplied typically) by the
     75   // renderer.  It queues the names, at minimal cost to the renderer's thread,
     76   // and allows this class to process them when time permits (in a later task).
     77   DnsQueue c_string_queue_;
     78 
     79 
     80   // domain_map_ contains (for each domain) one of the next two constants,
     81   // depending on whether we have asked the browser process to do the actual
     82   // DNS lookup.
     83   static const int kLookupRequested = 0x1;
     84   static const int kPending = 0x0;
     85   typedef std::map<std::string, int> DomainUseMap;
     86   DomainUseMap domain_map_;
     87 
     88   // Cache a tally of the count of names that haven't yet been sent
     89   // for DNS pre-fetching.  Note that we *could* recalculate this
     90   // count by iterating over domain_map_, looking for even values.
     91   size_t new_name_count_;
     92 
     93   // We have some metrics to examine performance.  We might use
     94   // these metrics to modify buffer counts etc. some day.
     95   int buffer_full_discard_count_;
     96   int numeric_ip_discard_count_;
     97 
     98   base::WeakPtrFactory<RendererNetPredictor> weak_factory_;
     99 
    100   DISALLOW_COPY_AND_ASSIGN(RendererNetPredictor);
    101 };  // class RendererNetPredictor
    102 
    103 #endif  // CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_
    104