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));
+  config_.max_concurrency = GetMaxConcurrency();
 }
 
 PrerenderManager::~PrerenderManager() {
 }
 
 void PrerenderManager::Shutdown() {
   DoShutdown();
 }
 
 PrerenderHandle* PrerenderManager::AddPrerenderFromLinkRelPrerender(
@@ skipping 339 matching lines @@
 // static
 const char* PrerenderManager::GetModeString() {
   switch (mode_) {
     case PRERENDER_MODE_DISABLED:
       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_MULTI_PRERENDER_GROUP:
+      return "_Multi";
     case PRERENDER_MODE_EXPERIMENT_5MIN_TTL_GROUP:
       return "_5MinTTL";
     case PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP:
       return "_NoUse";
     case PRERENDER_MODE_MAX:
       NOTREACHED() << "Invalid PrerenderManager mode.";
       break;
   };
   return "";
 }
@@ skipping 11 matching lines @@
 // static
 bool PrerenderManager::IsControlGroup() {
   return GetMode() == PRERENDER_MODE_EXPERIMENT_CONTROL_GROUP;
 }
 
 // static
 bool PrerenderManager::IsNoUseGroup() {
   return GetMode() == PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP;
 }
 
+// static
+size_t PrerenderManager::GetMaxConcurrency() {
+  if (GetMode() == PRERENDER_MODE_EXPERIMENT_MULTI_PRERENDER_GROUP)
+    return 3;
+  return 1;
+}
+
 bool PrerenderManager::IsWebContentsPrerendering(
     WebContents* web_contents) const {
   DCHECK(CalledOnValidThread());
   for (std::list<linked_ptr<PrerenderData> >::const_iterator it =
            active_prerender_list_.begin();
        it != active_prerender_list_.end();
        ++it) {
     TabContents* prerender_tab_contents =
         it->get()->contents_->prerender_contents();
     if (prerender_tab_contents &&
@@ skipping 339 matching lines @@
 
   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) {
+  DCHECK(Config::kMaximumMaxConcurrency >= config_.max_concurrency);

[dominich, 2012/07/23 18:45:56]

why is this important? if we want to experiment with 10, we shouldn't have to
update that in two places.

[mmenke, 2012/07/23 18:48:49]

Drive by nit:  DCHECK_GE

[gavinp, 2012/07/23 18:51:55]

This test guards the histograms sizing; the alternative was getters and setters
on the config object.

[gavinp, 2012/07/23 18:51:55]

DCHECK_GE won't work, as it takes a pointer to its arguments, and that is a
static const int, which doesn't have data segment extent if it isn't
dereferenced. So using DCHECK_GE will cause a linker error. Do you think it's
worth switching to DCHECK_GE if the cost is adding the const to a data segment?

[dominich, 2012/07/23 18:57:14]

in logging.h it uses const T& or int - I don't see any pointers being taken.

[gavinp, 2012/07/23 19:06:10]

Sorry, takes a reference.

+  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_->RecordConcurrency(active_prerender_list_.size());
+
   StartSchedulingPeriodicCleanups();
   return prerender_handle;
 }
 
 void PrerenderManager::StartSchedulingPeriodicCleanups() {
   DCHECK(CalledOnValidThread());
   if (repeating_timer_.IsRunning())
     return;
   repeating_timer_.Start(FROM_HERE,
       base::TimeDelta::FromMilliseconds(kPeriodicCleanupIntervalMs),
@@ skipping 260 matching lines @@
   if (!render_process_host || !render_process_host->GetBrowserContext())
     return NULL;
   Profile* profile = Profile::FromBrowserContext(
       render_process_host->GetBrowserContext());
   if (!profile)
     return NULL;
   return PrerenderManagerFactory::GetInstance()->GetForProfile(profile);
 }
 
 }  // namespace prerender