components/dns_prefetch/renderer/renderer_net_predictor.h

   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 COMPONENTS_DNS_PREFETCH_RENDERER_RENDERER_NET_PREDICTOR_H_
  22 #define COMPONENTS_DNS_PREFETCH_RENDERER_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 "components/dns_prefetch/renderer/predictor_queue.h"
  30
  31 namespace dns_prefetch {
  32
  33 class RendererNetPredictor {
  34  public:
  35   RendererNetPredictor();
  36   ~RendererNetPredictor();
  37
  38   // Push a name into the queue to be resolved.
  39   void Resolve(const char* name, size_t length);
  40
  41   // SubmitHosts processes the buffered names, and submits them for DNS
  42   // prefetching.
  43   // Note that browser process may decide which names should be looked up (to
  44   // pre-warm the cache) based on what has been (or not been) looked up
  45   // recently.
  46   // If sending for DNS lookup is incomplete (queue is not empty, or not all
  47   // names in map are sent, or ...) then a task to continue processing is
  48   // sent to our thread loop.
  49   void SubmitHostnames();
  50
  51   // The following is private, but exposed for testing purposes only.
  52   static bool is_numeric_ip(const char* name, size_t length);
  53
  54  private:
  55   // ExtractBufferedNames pulls names from queue into the map, reducing or
  56   // eliminating a waiting queue.
  57   // The size_goal argument can be used to reduce the amount of
  58   // processing done in this method, and can leave some data
  59   // in the buffer under some circumstances.
  60   // If size_goal is zero, then extraction proceeds until
  61   // the queue is empty.  If size goal is positive, then
  62   // extraction continues until the domain_map_ contains
  63   // at least the specified number of names, or the buffer is empty.
  64   void ExtractBufferedNames(size_t size_goal = 0);
  65
  66   // DnsPrefetchNames does not check the buffer, and just sends names
  67   // that are already collected in the domain_map_ for DNS lookup.
  68   // If max_count is zero, then all available names are sent; and
  69   // if positive, then at most max_count names will be sent.
  70   void DnsPrefetchNames(size_t max_count = 0);
  71
  72   // Reset() restores initial state provided after construction.
  73   // This discards ALL queue entries, and map entries.
  74   void Reset();
  75
  76   // We use c_string_queue_ to hold lists of names supplied typically) by the
  77   // renderer.  It queues the names, at minimal cost to the renderer's thread,
  78   // and allows this class to process them when time permits (in a later task).
  79   DnsQueue c_string_queue_;
  80
  81
  82   // domain_map_ contains (for each domain) one of the next two constants,
  83   // depending on whether we have asked the browser process to do the actual
  84   // DNS lookup.
  85   static const int kLookupRequested = 0x1;
  86   static const int kPending = 0x0;
  87   typedef std::map<std::string, int> DomainUseMap;
  88   DomainUseMap domain_map_;
  89
  90   // Cache a tally of the count of names that haven't yet been sent
  91   // for DNS pre-fetching.  Note that we *could* recalculate this
  92   // count by iterating over domain_map_, looking for even values.
  93   size_t new_name_count_;
  94
  95   // We have some metrics to examine performance.  We might use
  96   // these metrics to modify buffer counts etc. some day.
  97   int buffer_full_discard_count_;
  98   int numeric_ip_discard_count_;
  99
 100   base::WeakPtrFactory<RendererNetPredictor> weak_factory_;
 101
 102   DISALLOW_COPY_AND_ASSIGN(RendererNetPredictor);
 103 };  // class RendererNetPredictor
 104
 105 }  // namespace dns_prefetch
 106
 107 #endif  // COMPONENTS_DNS_PREFETCH_RENDERER_RENDERER_NET_PREDICTOR_H_