Componentize renderer side of DNS prefetching.

chrome/renderer/net/renderer_net_predictor.h

-// Copyright (c) 2011 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_
-
-#include <map>
-#include <string>
-
-#include "base/basictypes.h"
-#include "base/memory/weak_ptr.h"
-#include "chrome/renderer/net/predictor_queue.h"
-
-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_;
-
-  base::WeakPtrFactory<RendererNetPredictor> weak_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(RendererNetPredictor);
-};  // class RendererNetPredictor
-
-#endif  // CHROME_RENDERER_NET_RENDERER_NET_PREDICTOR_H_