text: // Copyright (c) 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.
  
  // A RendererNetPredictor instance is maintained for each RenderThread.
  // URL strings are typically added to the embedded queue during rendering.
  // The first addition to the queue (transitioning from empty to having
  // some names) causes a processing task to be added to the Renderer Thread.
  // The processing task gathers all buffered names, and send them via IPC
  // to the browser, so that DNS lookups can be performed before the user attempts
  // to traverse a link.
  // This class removed some duplicates, and discards numeric IP addresss
  // (which wouldn't looked up in DNS anyway).
  // To limit the time during the processing task (and avoid stalling the Render
  // thread), several limits are placed on how much of the queue to process.
  // If the processing task is not able to completely empty the queue, it
  // schedules a future continuation of the task, and keeps the map of already
  // sent names.  If the entire queue is processed, then the list of "sent names"
  // is cleared so that future gatherings might again pass along the same names.
  
  #ifndef CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_
  #define CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_
  #pragma once
  
  #include <map>
  #include <string>
  
  #include "base/basictypes.h"
  #include "base/task.h"
  #include "chrome/renderer/net/predictor_queue.h"
  
  // Global API consists to do Prefetching in renderer.  This uses IPC to reach
  // the Browser's global functions.
  void DnsPrefetchCString(const char* hostname, size_t length);
  
  class RendererNetPredictor {
   public:
    RendererNetPredictor();
    ~RendererNetPredictor();
  
    // Push a name into the queue to be resolved.
    void Resolve(const char* name, size_t length);
  
    // SubmitHosts processes the buffered names, and submits them for DNS
    // prefetching.
    // Note that browser process may decide which names should be looked up (to
    // pre-warm the cache) based on what has been (or not been) looked up
    // recently.
    // If sending for DNS lookup is incomplete (queue is not empty, or not all
    // names in map are sent, or ...) then a task to continue processing is
    // sent to our thread loop.
    void SubmitHostnames();
  
    // The following is private, but exposed for testing purposes only.
    static bool is_numeric_ip(const char* name, size_t length);
  
   private:
    // ExtractBufferedNames pulls names from queue into the map, reducing or
    // eliminating a waiting queue.
    // The size_goal argument can be used to reduce the amount of
    // processing done in this method, and can leave some data
    // in the buffer under some circumstances.
    // If size_goal is zero, then extraction proceeds until
    // the queue is empty.  If size goal is positive, then
    // extraction continues until the domain_map_ contains
    // at least the specified number of names, or the buffer is empty.
    void ExtractBufferedNames(size_t size_goal = 0);
  
    // DnsPrefetchNames does not check the buffer, and just sends names
    // that are already collected in the domain_map_ for DNS lookup.
    // If max_count is zero, then all available names are sent; and
    // if positive, then at most max_count names will be sent.
    void DnsPrefetchNames(size_t max_count = 0);
  
    // Reset() restores initial state provided after construction.
    // This discards ALL queue entries, and map entries.
    void Reset();
  
    // We use c_string_queue_ to hold lists of names supplied typically) by the
    // renderer.  It queues the names, at minimal cost to the renderer's thread,
    // and allows this class to process them when time permits (in a later task).
    DnsQueue c_string_queue_;
  
  
    // domain_map_ contains (for each domain) one of the next two constants,
    // depending on whether we have asked the browser process to do the actual
    // DNS lookup.
    static const int kLookupRequested = 0x1;
    static const int kPending = 0x0;
    typedef std::map<std::string, int> DomainUseMap;
    DomainUseMap domain_map_;
  
    // Cache a tally of the count of names that haven't yet been sent
    // for DNS pre-fetching.  Note that we *could* recalculate this
    // count by iterating over domain_map_, looking for even values.
    size_t new_name_count_;
  
    // We have some metrics to examine performance.  We might use
    // these metrics to modify buffer counts etc. some day.
    int buffer_full_discard_count_;
    int numeric_ip_discard_count_;
  
    ScopedRunnableMethodFactory<RendererNetPredictor> renderer_predictor_factory_;
  
    DISALLOW_COPY_AND_ASSIGN(RendererNetPredictor);
  };  // class RendererNetPredictor
  
  #endif  // CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_
  