Make three simultanious prerenders the default maximum in Canary and Dev only.

chrome/browser/prerender/prerender_manager.cc

 // Copyright (c) 2012 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 <algorithm>
 #include <functional>
 #include <string>
 #include <vector>
@@ skipping 51 matching lines @@
 
 namespace {
 
 // Time window for which we will record windowed PLT's from the last
 // observed link rel=prefetch tag.
 const int kWindowDurationSeconds = 30;
 
 // Time interval at which periodic cleanups are performed.
 const int kPeriodicCleanupIntervalMs = 1000;
 
-// Time interval before a new prerender is allowed.
-const int kMinTimeBetweenPrerendersMs = 500;
-
 // Valid HTTP methods for prerendering.
 const char* const kValidHttpMethods[] = {
   "GET",
   "HEAD",
   "OPTIONS",
   "POST",
   "TRACE",
 };
 
 // Length of prerender history, for display in chrome://net-internals
@@ skipping 104 matching lines @@
       last_prerender_start_time_(GetCurrentTimeTicks() -
           base::TimeDelta::FromMilliseconds(kMinTimeBetweenPrerendersMs)),
       weak_factory_(this),
       prerender_history_(new PrerenderHistory(kHistoryLength)),
       histograms_(new PrerenderHistograms()),
       local_predictor_(new PrerenderLocalPredictor(this)) {
   // There are some assumptions that the PrerenderManager is on the UI thread.
   // Any other checks simply make sure that the PrerenderManager is accessed on
   // the same thread that it was created on.
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  if (GetMode() == PRERENDER_MODE_EXPERIMENT_ONE_PRERENDER_GROUP) {
+    config_.max_concurrency = 1;
+  }
 }
 
 PrerenderManager::~PrerenderManager() {
 }
 
 void PrerenderManager::Shutdown() {
   DoShutdown();
 }
 
 PrerenderHandle* PrerenderManager::AddPrerenderFromLinkRelPrerender(
@@ skipping 343 matching lines @@
       return "_Disabled";
     case PRERENDER_MODE_ENABLED:
     case PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP:
       return "_Enabled";
     case PRERENDER_MODE_EXPERIMENT_CONTROL_GROUP:
       return "_Control";
     case PRERENDER_MODE_EXPERIMENT_5MIN_TTL_GROUP:
       return "_5MinTTL";
     case PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP:
       return "_NoUse";
+    case PRERENDER_MODE_EXPERIMENT_ONE_PRERENDER_GROUP:
+      return "_One";
     case PRERENDER_MODE_MAX:
       NOTREACHED() << "Invalid PrerenderManager mode.";
       break;
   };
   return "";
 }
 
 // static
 bool PrerenderManager::IsPrerenderingPossible() {
   return GetMode() != PRERENDER_MODE_DISABLED;
@@ skipping 349 matching lines @@
     // by a navigation and is unlikely to be the same site.
     RecordFinalStatus(origin, experiment, FINAL_STATUS_RATE_LIMIT_EXCEEDED);
     return NULL;
   }
 
   PrerenderContents* prerender_contents = CreatePrerenderContents(
       url, referrer, origin, experiment);
   if (!prerender_contents || !prerender_contents->Init())
     return NULL;
 
-  histograms_->RecordPrerenderStarted(origin);
-
   // TODO(cbentzel): Move invalid checks here instead of PrerenderContents?
   active_prerender_list_.push_back(
       linked_ptr<PrerenderData>(new PrerenderData(this, prerender_contents)));
   PrerenderHandle* prerender_handle =
       new PrerenderHandle(active_prerender_list_.back().get());
 
   last_prerender_start_time_ = GetCurrentTimeTicks();
 
   gfx::Size contents_size =
       size.IsEmpty() ? config_.default_tab_bounds.size() : size;
 
   prerender_contents->StartPrerendering(process_id, contents_size,
                                         session_storage_namespace,
                                         control_group_behavior);
 
-  while (active_prerender_list_.size() > config_.max_elements) {
+  while (active_prerender_list_.size() > config_.max_concurrency) {
     prerender_contents = active_prerender_list_.front()->contents_;
     DCHECK(prerender_contents);
     prerender_contents->Destroy(FINAL_STATUS_EVICTED);
   }
 
+  histograms_->RecordPrerenderStarted(origin, active_prerender_list_.size());

[dominich, 2012/07/19 16:04:38]

changing this is bad - we'll have a mismatch between started and evicted which
Omnibox stats rely on.

Instead, record started as before and maybe separate the count tracking and do
that here.

[gavinp, 2012/07/23 18:35:21]

Done.

+
   StartSchedulingPeriodicCleanups();
   return prerender_handle;
 }
 
 void PrerenderManager::StartSchedulingPeriodicCleanups() {
   DCHECK(CalledOnValidThread());
   if (repeating_timer_.IsRunning())
     return;
   repeating_timer_.Start(FROM_HERE,
       base::TimeDelta::FromMilliseconds(kPeriodicCleanupIntervalMs),
@@ skipping 261 matching lines @@
     return NULL;
   Profile* profile = Profile::FromBrowserContext(
       render_process_host->GetBrowserContext());
   if (!profile)
     return NULL;
   return PrerenderManagerFactory::GetInstance()->GetForProfile(profile);
 }
 
 }  // namespace prerender