Add pending preloads indexed by routing id. Start preloading once we navigate.

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index d30bc9135c9e81f2c3f35701dae39a972a8a6b4c..dedfdf223ec3eebdfcbf37e6f7750cc535c60365 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -53,6 +53,17 @@ struct PrerenderManager::PrerenderContentsData {
   }
 };
 
+struct PrerenderManager::PendingContentsData {
+  PendingContentsData(const GURL& url, const std::vector<GURL>& alias_urls,
+                      const GURL& referrer)
+      : url_(url), alias_urls_(alias_urls), referrer_(referrer) { }
+  ~PendingContentsData() {}
+  GURL url_;
+  std::vector<GURL> alias_urls_;
+  GURL referrer_;
+};
+
+
 PrerenderManager::PrerenderManager(Profile* profile)
     : profile_(profile),
       max_prerender_age_(base::TimeDelta::FromSeconds(
@@ -107,6 +118,46 @@ bool PrerenderManager::AddPreload(const GURL& url,
   return true;
 }
 
+void PrerenderManager::AddPendingPreload(
+    const std::pair<int,int>& child_route_id_pair,
+    const GURL& url,
+    const std::vector<GURL>& alias_urls,
+    const GURL& referrer) {
+  // Check if this is coming from a valid prerender rvh.
+  bool is_valid_prerender = false;
+  for (std::list<PrerenderContentsData>::iterator it = prerender_list_.begin();
+       it != prerender_list_.end(); ++it) {

[cbentzel, 2011/03/18 18:35:43]

This is a pretty subtle case. Could you add a test for it? It may be easier to
do with a prerender_manager_unittest rather than a browser test. 

[dominich, 2011/03/21 16:36:11]

Done.

+    PrerenderContents* pc = it->contents_;
+    const RenderViewHost* rvh = pc->render_view_host();
+    if (rvh &&
+        rvh->process() &&

[cbentzel, 2011/03/18 18:35:43]

You don't check for process() in RemovePendingPreload below, is it needed?

[dominich, 2011/03/21 16:36:11]

Actually no - I checked that when I wrote RemovePendingPreload but didn't check
when I wrote this one, and apparently my memory is terrible.

Done.

+        rvh->process()->id() == child_route_id_pair.first &&
+        rvh->routing_id() == child_route_id_pair.second) {
+      is_valid_prerender = true;
+      break;
+    }
+  }
+
+  // If not, we could check to see if the RenderViewHost specified by the
+  // child_route_id_pair exists and if so just start prerendering, as this
+  // suggests that the link was clicked, though this might prerender something
+  // that the user has already navigated away from. For now, we'll be
+  // conservative and skip the prerender which will mean some prerender requests
+  // from prerendered pages will be missed if the user navigates quickly.

[cbentzel, 2011/03/18 18:35:43]

Should you add a FINAL_STATUS entry here? This is equivalent to a missed chance
for prerendering. 

[dominich, 2011/03/21 16:36:11]

I thought about it, but we're not creating the prerender and then throwing it
away so I didn't think there were wasted resources. However you're right that
it's good to track any time we fail to prerender when we can as if it's a high
rate we might want to follow the advice in the comment. Thanks for pointing that
out.

+  if (!is_valid_prerender)

[cbentzel, 2011/03/18 18:35:43]

Thanks for the comment here.

+    return;
+
+  PendingPrerenderList::iterator it =
+      pending_prerender_list_.find(child_route_id_pair);
+  if (it == pending_prerender_list_.end()) {
+    PendingPrerenderList::value_type el = std::make_pair(child_route_id_pair,
+                                            std::vector<PendingContentsData>());
+    it = pending_prerender_list_.insert(el).first;
+  }
+
+  it->second.push_back(PendingContentsData(url, alias_urls, referrer));
+}
+
 void PrerenderManager::DeleteOldEntries() {
   while (!prerender_list_.empty()) {
     PrerenderContentsData data = prerender_list_.front();
@@ -155,6 +206,22 @@ bool PrerenderManager::MaybeUsePreloadedPage(TabContents* tc, const GURL& url) {
   tc->SwapInRenderViewHost(rvh);
   MarkTabContentsAsPrerendered(tc);
 
+  // See if we have any pending prerender requests for this routing id and start
+  // the preload if we do.
+  std::pair<int, int> child_route_pair = std::make_pair(rvh->process()->id(),
+                                                        rvh->routing_id());
+  PendingPrerenderList::iterator pending_it =
+      pending_prerender_list_.find(child_route_pair);
+  if (pending_it != pending_prerender_list_.end()) {
+    for (std::vector<PendingContentsData>::iterator content_it =
+            pending_it->second.begin();
+         content_it != pending_it->second.end(); ++content_it) {
+      AddPreload(content_it->url_, content_it->alias_urls_,
+                 content_it->referrer_);
+    }
+    pending_prerender_list_.erase(pending_it);
+  }
+
   ViewHostMsg_FrameNavigate_Params* p = pc->navigate_params();
   if (p != NULL)
     tc->DidNavigate(rvh, *p);
@@ -179,6 +246,7 @@ void PrerenderManager::RemoveEntry(PrerenderContents* entry) {
        it != prerender_list_.end();
        ++it) {
     if (it->contents_ == entry) {
+      RemovePendingPreload(entry);
       prerender_list_.erase(it);
       break;
     }
@@ -241,6 +309,23 @@ PrerenderContents* PrerenderManager::FindEntry(const GURL& url) {
   return NULL;
 }
 
+PrerenderManager::PendingContentsData*
+    PrerenderManager::FindPendingEntry(const GURL& url) {
+  for (PendingPrerenderList::iterator map_it = pending_prerender_list_.begin();
+       map_it != pending_prerender_list_.end();
+       ++map_it) {
+    for (std::vector<PendingContentsData>::iterator content_it =
+            map_it->second.begin();
+         content_it != map_it->second.end();
+         ++content_it) {
+      if (content_it->url_ == url)
+        return &(*content_it);
+    }
+  }
+
+  return NULL;
+}
+
 // static
 void PrerenderManager::RecordPrefetchTagObserved() {
   // Ensure that we are in the UI thread, and post to the UI thread if
@@ -267,6 +352,19 @@ void PrerenderManager::RecordPrefetchTagObservedOnUIThread() {
   last_prefetch_seen_time_ = base::TimeTicks::Now();
 }
 
+void PrerenderManager::RemovePendingPreload(PrerenderContents* entry) {

[cbentzel, 2011/03/18 18:35:43]

can |entry| be const? 

[dominich, 2011/03/21 16:36:11]

no - render_view_host() is not const.

Is there precedence for having a const version of accessors? Based on the style
guide having a const overload would be a bad thing, but how about
render_view_host_const()?

+  RenderViewHost* rvh = entry->render_view_host();
+
+  // If the entry doesn't have a RenderViewHost then it didn't start
+  // prerendering and there shouldn't be any pending preloads to remove.
+  if (rvh == NULL)
+    return;
+
+  std::pair<int, int> child_route_pair = std::make_pair(rvh->process()->id(),
+                                                        rvh->routing_id());
+  pending_prerender_list_.erase(child_route_pair);
+}
+
 // static
 bool PrerenderManager::ShouldRecordWindowedPPLT() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));