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

chrome/browser/prerender/prerender_manager.cc

 // 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.
 
 #include "chrome/browser/prerender/prerender_manager.h"
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
@@ skipping 36 matching lines @@
 struct PrerenderManager::PrerenderContentsData {
   PrerenderContents* contents_;
   base::Time start_time_;
   PrerenderContentsData(PrerenderContents* contents, base::Time start_time)
       : contents_(contents),
         start_time_(start_time) {
   }
 };
 
 PrerenderManager::PrerenderManager(Profile* profile)
-    : profile_(profile),
+    : rate_limit_enabled_(true),
+      profile_(profile),
       max_prerender_age_(base::TimeDelta::FromSeconds(
           kDefaultMaxPrerenderAgeSeconds)),
       max_elements_(kDefaultMaxPrerenderElements),
-      prerender_contents_factory_(PrerenderContents::CreateFactory()) {
+      prerender_contents_factory_(PrerenderContents::CreateFactory()),
+      last_prerender_start_time_(GetCurrentTimeTicks() -
+          base::TimeDelta::FromMilliseconds(kMinTimeBetweenPrerendersMs)) {
 }
 
 PrerenderManager::~PrerenderManager() {
   while (!prerender_list_.empty()) {
     PrerenderContentsData data = prerender_list_.front();
     prerender_list_.pop_front();
     data.contents_->set_final_status(FINAL_STATUS_MANAGER_SHUTDOWN);
     delete data.contents_;
   }
 }
@@ skipping 13 matching lines @@
   // Do not prerender if there are too many render processes, and we would
   // have to use an existing one.  We do not want prerendering to happen in
   // a shared process, so that we can always reliably lower the CPU
   // priority for prerendering.
   // TODO(tburkard): Figure out how to cancel prerendering in the opposite
   // case, when a new tab is added to a process used for prerendering.
   if (RenderProcessHost::ShouldTryToUseExistingProcessHost()) {
     RecordFinalStatus(FINAL_STATUS_TOO_MANY_PROCESSES);
     return false;
   }
+
+  // Check if enough time has passed since the last prerender.
+  if (!DoesRateLimitAllowPrerender()) {
+    // Cancel the prerender. We could add it to the pending prerender list but
+    // this doesn't make sense as the next prerender request will be triggered
+    // by a navigation and is unlikely to be the same site.
+    RecordFinalStatus(FINAL_STATUS_RATE_LIMIT_EXCEEDED);
+    return false;
+  }
+
   // TODO(cbentzel): Move invalid checks here instead of PrerenderContents?
   PrerenderContentsData data(CreatePrerenderContents(url, alias_urls, referrer),
                              GetCurrentTime());
   prerender_list_.push_back(data);
+  last_prerender_start_time_ = GetCurrentTimeTicks();
   data.contents_->StartPrerendering();
   while (prerender_list_.size() > max_elements_) {
     data = prerender_list_.front();
     prerender_list_.pop_front();
     data.contents_->set_final_status(FINAL_STATUS_EVICTED);
     delete data.contents_;
   }
   StartSchedulingPeriodicCleanups();
   return true;
 }
@@ skipping 27 matching lines @@
   return NULL;
 }
 
 bool PrerenderManager::MaybeUsePreloadedPage(TabContents* tc, const GURL& url) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   scoped_ptr<PrerenderContents> pc(GetEntry(url));
   if (pc.get() == NULL)
     return false;
 
   if (!pc->load_start_time().is_null())
-    RecordTimeUntilUsed(base::TimeTicks::Now() - pc->load_start_time());
+    RecordTimeUntilUsed(GetCurrentTimeTicks() - pc->load_start_time());
   pc->set_final_status(FINAL_STATUS_USED);
 
   RenderViewHost* rvh = pc->render_view_host();
   // RenderViewHosts in PrerenderContents start out hidden.
   // Since we are actually using it now, restore it.
   rvh->WasRestored();
   pc->set_render_view_host(NULL);
   rvh->Send(new ViewMsg_DisplayPrerenderedPage(rvh->routing_id()));
   tc->SwapInRenderViewHost(rvh);
   MarkTabContentsAsPrerendered(tc);
@@ skipping 26 matching lines @@
       break;
     }
   }
   DeleteOldEntries();
 }
 
 base::Time PrerenderManager::GetCurrentTime() const {
   return base::Time::Now();
 }
 
+base::TimeTicks PrerenderManager::GetCurrentTimeTicks() const {
+  return base::TimeTicks::Now();
+}
+
 bool PrerenderManager::IsPrerenderElementFresh(const base::Time start) const {
   base::Time now = GetCurrentTime();
   return (now - start < max_prerender_age_);
 }
 
 PrerenderContents* PrerenderManager::CreatePrerenderContents(
     const GURL& url,
     const std::vector<GURL>& alias_urls,
     const GURL& referrer) {
   return prerender_contents_factory_->CreatePrerenderContents(
@@ skipping 67 matching lines @@
 // static
 bool PrerenderManager::ShouldRecordWindowedPPLT() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (last_prefetch_seen_time_.is_null())
     return false;
   base::TimeDelta elapsed_time =
       base::TimeTicks::Now() - last_prefetch_seen_time_;
   return elapsed_time <= base::TimeDelta::FromSeconds(kWindowedPPLTSeconds);
 }
 
+bool PrerenderManager::DoesRateLimitAllowPrerender() const {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  base::TimeDelta elapsed_time =
+      GetCurrentTimeTicks() - last_prerender_start_time_;
+  UMA_HISTOGRAM_TIMES("Prerender.TimeBetweenPrerenderRequests",
+                      elapsed_time);
+  if (!rate_limit_enabled_)
+    return true;
+  return elapsed_time >
+      base::TimeDelta::FromMilliseconds(kMinTimeBetweenPrerendersMs);
+}
+
 void PrerenderManager::StartSchedulingPeriodicCleanups() {
   if (repeating_timer_.IsRunning())
     return;
   repeating_timer_.Start(
       base::TimeDelta::FromMilliseconds(kPeriodicCleanupIntervalMs),
       this,
       &PrerenderManager::PeriodicCleanup);
 }
 
 void PrerenderManager::StopSchedulingPeriodicCleanups() {
@@ skipping 24 matching lines @@
 
 void PrerenderManager::MarkTabContentsAsNotPrerendered(TabContents* tc) {
   prerendered_tc_set_.erase(tc);
 }
 
 bool PrerenderManager::IsTabContentsPrerendered(TabContents* tc) const {
   return prerendered_tc_set_.count(tc) > 0;
 }
 
 }  // namespace prerender