Limit prerender by only allowing one every X ms (X currently set to 500).

chrome/browser/prerender/prerender_manager.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.
 
 #ifndef CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 #pragma once
 
 #include <list>
 #include <vector>
@@ skipping 79 matching lines @@
   // The following static method can be called from any thread, but will result
   // in posting a task to the UI thread if we are not in the UI thread.
   static void RecordPrefetchTagObserved();
 
   // Maintaining and querying the set of TabContents belonging to this
   // PrerenderManager that are currently showing prerendered pages.
   void MarkTabContentsAsPrerendered(TabContents* tc);
   void MarkTabContentsAsNotPrerendered(TabContents* tc);
   bool IsTabContentsPrerendered(TabContents* tc) const;
 
+  static void set_rate_limit_enabled(bool enable) {
+    rate_limit_enabled_ = enable;
+  }
+
  protected:
   virtual ~PrerenderManager();
 
   void SetPrerenderContentsFactory(
       PrerenderContents::Factory* prerender_contents_factory);
 
  private:
   // Test that needs needs access to internal functions.
   friend class PrerenderBrowserTest;
 
@@ skipping 19 matching lines @@
 
   // Finds the specified PrerenderContents and returns it, if it exists.
   // Returns NULL otherwise.  Unlike GetEntry, the PrerenderManager maintains
   // ownership of the PrerenderContents.
   PrerenderContents* FindEntry(const GURL& url);
 
   static bool ShouldRecordWindowedPPLT();
 
   static void RecordPrefetchTagObservedOnUIThread();
 
+  static bool DoesRateLimitAllowPrerender();
+
   Profile* profile_;
 
   base::TimeDelta max_prerender_age_;
   unsigned int max_elements_;
 
   // List of prerendered elements.
   std::list<PrerenderContentsData> prerender_list_;
 
   // Set of TabContents which are currently displaying a prerendered page.
   base::hash_set<TabContents*> prerendered_tc_set_;
 
   // Default maximum permitted elements to prerender.
   static const unsigned int kDefaultMaxPrerenderElements = 1;
 
   // Default maximum age a prerendered element may have, in seconds.
   static const int kDefaultMaxPrerenderAgeSeconds = 20;
 
   // Time window for which we will record windowed PLT's from the last
   // observed link rel=prefetch tag.
   static const int kWindowedPPLTSeconds = 30;
 
   // Time interval at which periodic cleanups are performed.
   static const int kPeriodicCleanupIntervalMs = 1000;
 
+  // Time interval before a new prerender is allowed.
+  static const int kMinTimeBetweenPrerendersMs = 500;

[tburkard, 2011/03/11 22:57:40]

I think we should set this to 1s.

[dominich, 2011/03/11 23:14:57]

I originally had it at 1s but felt it was too long. I did some vaguely empirical
testing by running searches and could easily get two searches in under 1s.

As this is only meant to catch a situation where we're being flooded, I felt
that 500 was a good balance. Do you have reason to think otherwise?

+
   scoped_ptr<PrerenderContents::Factory> prerender_contents_factory_;
 
   static PrerenderManagerMode mode_;
 
   // The time when we last saw a prefetch request coming from a renderer.
   // This is used to record perceived PLT's for a certain amount of time
   // from the point that we last saw a <link rel=prefetch> tag.
   // This static variable should only be modified on the UI thread.
   static base::TimeTicks last_prefetch_seen_time_;
 
   // RepeatingTimer to perform periodic cleanups of pending prerendered
   // pages.
   base::RepeatingTimer<PrerenderManager> repeating_timer_;
 
+  // Track time of last prerender to limit prerender spam.
+  // TODO(dominich): This could be an average rate instead of a single time
+  static base::TimeTicks last_prerender_start_time_;
+  static bool rate_limit_enabled_;
+
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };
 
 }  // prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_