Safely cancel prerenders on threads other than the UI thread

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 <string>
 
 #include "base/logging.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/favicon/favicon_tab_helper.h"
 #include "chrome/browser/prerender/prerender_contents.h"
 #include "chrome/browser/prerender/prerender_final_status.h"
+#include "chrome/browser/prerender/prerender_tracker.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/tab_contents/tab_contents_wrapper.h"
 #include "chrome/browser/ui/tab_contents/tab_contents_wrapper_delegate.h"
 #include "chrome/common/render_messages.h"
 #include "content/browser/browser_thread.h"
 #include "content/browser/renderer_host/render_view_host.h"
 #include "content/browser/renderer_host/render_process_host.h"
 #include "content/browser/renderer_host/resource_dispatcher_host.h"
 #include "content/browser/tab_contents/render_view_host_manager.h"
 #include "content/browser/tab_contents/tab_contents.h"
@@ skipping 344 matching lines @@
     prerender_contents->Destroy(final_status);
   }
 }
 
 void PrerenderManager::DeleteOldEntries() {
   DCHECK(CalledOnValidThread());
   while (!prerender_list_.empty()) {
     PrerenderContentsData data = prerender_list_.front();
     if (IsPrerenderElementFresh(data.start_time_))
       return;
-    prerender_list_.pop_front();
-    data.contents_->set_final_status(FINAL_STATUS_TIMED_OUT);
-    delete data.contents_;
+    data.contents_->Destroy(FINAL_STATUS_TIMED_OUT);
   }
   MaybeStopSchedulingPeriodicCleanups();
 }
 
 PrerenderContents* PrerenderManager::GetEntryButNotSpecifiedTC(
     const GURL& url,
     TabContents *tc) {
   DCHECK(CalledOnValidThread());
   DeleteOldEntries();
   DeletePendingDeleteEntries();
@@ skipping 26 matching lines @@
     return false;
 
   // If we are just in the control group (which can be detected by noticing
   // that prerendering hasn't even started yet), record that |tab_contents| now
   // would be showing a prerendered contents, but otherwise, don't do anything.
   if (!prerender_contents->prerendering_has_started()) {
     MarkTabContentsAsWouldBePrerendered(tab_contents);
     return false;
   }
 
+  int child_id, route_id;
+  CHECK(prerender_contents->GetChildId(&child_id));
+  CHECK(prerender_contents->GetRouteId(&route_id));
+
+  // Try to set the prerendered page as used, so any subsequent attempts to
+  // cancel on other threads will fail.  If this fails because the prerender
+  // was already cancelled, possibly on another thread, fail.
+  if (!PrerenderTracker::GetInstance()->TryUse(child_id, route_id))
+    return false;
+
   if (!prerender_contents->load_start_time().is_null())
     RecordTimeUntilUsed(GetCurrentTimeTicks() -
                         prerender_contents->load_start_time());
 
   UMA_HISTOGRAM_COUNTS("Prerender.PrerendersPerSessionCount",
                        ++prerenders_per_session_count_);
   prerender_contents->set_final_status(FINAL_STATUS_USED);
 
-  int child_id;
-  int route_id;
-  CHECK(prerender_contents->GetChildId(&child_id));
-  CHECK(prerender_contents->GetRouteId(&route_id));
-
   RenderViewHost* render_view_host =
       prerender_contents->render_view_host_mutable();
   prerender_contents->set_render_view_host(NULL);
 
   // RenderViewHosts in PrerenderContents start out hidden.
   // Since we are actually using it now, restore it.
   render_view_host->WasRestored();
   render_view_host->Send(
       new ViewMsg_SetIsPrerendering(render_view_host->routing_id(), false));
   tab_contents->SwapInRenderViewHost(render_view_host);
@@ skipping 59 matching lines @@
     return false;
 
   // If we are just in the control group (which can be detected by noticing
   // that prerendering hasn't even started yet), record that |tab_contents| now
   // would be showing a prerendered contents, but otherwise, don't do anything.
   if (!prerender_contents->prerendering_has_started()) {
     MarkTabContentsAsWouldBePrerendered(tab_contents);
     return false;
   }
 
+  int child_id, route_id;
+  CHECK(prerender_contents->GetChildId(&child_id));
+  CHECK(prerender_contents->GetRouteId(&route_id));
+
+  // Try to set the prerendered page as used, so any subsequent attempts to
+  // cancel on other threads will fail.  If this fails because the prerender
+  // was already cancelled, possibly on another thread, fail.
+  if (!PrerenderTracker::GetInstance()->TryUse(child_id, route_id))
+    return false;
+
   if (!prerender_contents->load_start_time().is_null())
     RecordTimeUntilUsed(GetCurrentTimeTicks() -
                         prerender_contents->load_start_time());
 
   UMA_HISTOGRAM_COUNTS("Prerender.PrerendersPerSessionCount",
                        ++prerenders_per_session_count_);
   prerender_contents->set_final_status(FINAL_STATUS_USED);
 
-  int child_id;
-  int route_id;
-  CHECK(prerender_contents->GetChildId(&child_id));
-  CHECK(prerender_contents->GetRouteId(&route_id));
-
   RenderViewHost* render_view_host =
       prerender_contents->prerender_contents()->render_view_host();
   DCHECK(render_view_host);
   render_view_host->Send(
       new ViewMsg_SetIsPrerendering(render_view_host->routing_id(), false));
 
   TabContentsWrapper* new_tab_contents =
       prerender_contents->ReleasePrerenderContents();
   TabContentsWrapper* old_tab_contents =
       TabContentsWrapper::GetCurrentWrapperForContents(tab_contents);
@@ skipping 367 matching lines @@
   return prerendered_tab_contents_set_.count(tab_contents) > 0;
 }
 
 bool PrerenderManager::WouldTabContentsBePrerendered(
     TabContents* tab_contents) const {
   DCHECK(CalledOnValidThread());
   return would_be_prerendered_tab_contents_set_.count(tab_contents) > 0;
 }
 
 }  // namespace prerender