Safely cancel prerenders on threads other than the UI thread

chrome/browser/prerender/prerender_tracker.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 "base/logging.h"
+#include "chrome/browser/prerender/prerender_manager.h"
+#include "chrome/browser/prerender/prerender_tracker.h"
+#include "content/browser/browser_thread.h"
+
+namespace prerender {
+
+namespace {
+
+void DestroyPreloadForRenderView(
+    const base::WeakPtr<PrerenderManager>& prerender_manager_weak_ptr,
+    int child_id,
+    int route_id,
+    FinalStatus final_status) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  PrerenderManager* prerender_manager = prerender_manager_weak_ptr.get();
+  if (!prerender_manager)
+    return;
+
+  prerender_manager->DestroyPreloadForChildRouteIdPair(
+      std::make_pair(child_id, route_id),
+      final_status);
+}
+
+}  // namespace
+
+struct RenderViewInfo {
+  FinalStatus final_status;

[dominich, 2011/05/19 16:07:27]

Should this have a constructor that takes the PrerenderManager* and sets the
final_status to FINAL_STATUS_MAX? 

[mmenke, 2011/05/19 16:40:42]

In order to do that, I'd also have to make a constructor that takes no
arguments, since std::map works by creating a new entry with that constructor,
and then copying the data over.  Creating such an extra constructor for that
seems a little crufty.

I've switched to creating it on the stack and then inserting it, to avoid the
double lookup the old code produced, though I'm open to other ideas.

[dominich, 2011/05/19 16:55:47]

I think that's only if you use operator[]. If you use:

map->insert(std::make_pair(child_route_id_pair,
RenderViewInfo(prerender_manager)));

Then you don't get the lookup or the empty constructor call. It's not exactly
performance critical, but it means the RenderViewInfo is a self-contained type
with sensible default values set at construction.

[mmenke, 2011/05/19 17:19:10]

You're right.  Done as you suggest.

+  base::WeakPtr<PrerenderManager> prerender_manager;
+};
+
+// static
+PrerenderTracker* PrerenderTracker::GetInstance() {
+  return Singleton<PrerenderTracker>::get();
+}
+
+bool PrerenderTracker::TryUse(int child_id, int route_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  FinalStatus final_status = SetFinalStatus(child_id, route_id,
+                                            FINAL_STATUS_USED);
+  return final_status == FINAL_STATUS_USED;
+}
+
+bool PrerenderTracker::TryCancel(
+    int child_id,
+    int route_id,
+    FinalStatus final_status) {
+  DCHECK_NE(FINAL_STATUS_USED, final_status);
+  DCHECK(final_status >= 0 && final_status < FINAL_STATUS_MAX);
+
+  final_status = SetFinalStatus(child_id, route_id, final_status);
+  return final_status != FINAL_STATUS_USED && final_status != FINAL_STATUS_MAX;
+}
+
+bool PrerenderTracker::TryCancelOnIOThread(
+    int child_id,
+    int route_id,
+    FinalStatus final_status) {
+  DCHECK_NE(FINAL_STATUS_USED, final_status);
+  DCHECK(final_status >= 0 && final_status < FINAL_STATUS_MAX);
+
+  if (!IsPrerenderingOnIOThread(child_id, route_id))
+    return false;
+  return TryCancel(child_id, route_id, final_status);
+}
+
+bool PrerenderTracker::IsPrerenderingOnIOThread(int child_id, int route_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  std::pair<int, int> child_route_id_pair(child_id, route_id);
+  return possibly_prerendering_io_thread_set_.end() !=
+         possibly_prerendering_io_thread_set_.find(child_route_id_pair);
+}
+
+bool PrerenderTracker::GetFinalStatus(int child_id, int route_id,
+                                      FinalStatus* final_status) {
+  std::pair<int, int> child_route_id_pair(child_id, route_id);
+
+  base::AutoLock lock(lock_);
+  FinalStatusMap::iterator final_status_it =
+      final_status_map_.find(child_route_id_pair);
+  if (final_status_map_.end() == final_status_map_.find(child_route_id_pair))
+    return false;
+  *final_status = final_status_it->second.final_status;
+  return true;
+}
+
+void PrerenderTracker::OnPrerenderingStarted(
+    int child_id, int route_id, PrerenderManager* prerender_manager) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK_NE(-1, child_id);
+  DCHECK_NE(-1, route_id);
+
+  std::pair<int, int> child_route_id_pair(child_id, route_id);
+
+  // The RenderView should not already be prerendering.
+  DCHECK(final_status_map_.end() ==
+         final_status_map_.find(child_route_id_pair));
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      NewRunnableFunction(&AddPrerenderOnIOThreadTask, child_route_id_pair));
+
+  base::AutoLock lock(lock_);
+  final_status_map_[child_route_id_pair].final_status = FINAL_STATUS_MAX;
+  final_status_map_[child_route_id_pair].prerender_manager =
+      prerender_manager->AsWeakPtr();
+}
+
+void PrerenderTracker::OnPrerenderingFinished(int child_id, int route_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK_NE(-1, child_id);
+  DCHECK_NE(-1, route_id);
+
+  std::pair<int, int> child_route_id_pair(child_id, route_id);
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      NewRunnableFunction(&RemovePrerenderOnIOThreadTask, child_route_id_pair));
+
+  base::AutoLock lock(lock_);
+  size_t num_erased = final_status_map_.erase(child_route_id_pair);
+  DCHECK_EQ(1u, num_erased);
+}
+
+PrerenderTracker::PrerenderTracker() {
+}
+
+PrerenderTracker::~PrerenderTracker() {
+}
+
+FinalStatus PrerenderTracker::SetFinalStatus(int child_id, int route_id,
+                                             FinalStatus final_status) {
+  DCHECK(final_status >= FINAL_STATUS_USED && final_status < FINAL_STATUS_MAX);
+
+  std::pair<int, int> child_route_id_pair(child_id, route_id);
+
+  base::AutoLock lock(lock_);
+  FinalStatusMap::iterator final_status_it =
+      final_status_map_.find(child_route_id_pair);
+  if (final_status_it == final_status_map_.end()) {
+    // The RenderView has already been either used or destroyed.
+    return FINAL_STATUS_MAX;
+  }
+
+  if (final_status_it->second.final_status == FINAL_STATUS_MAX) {
+    final_status_it->second.final_status = final_status;
+    if (final_status != FINAL_STATUS_USED) {
+      BrowserThread::PostTask(
+          BrowserThread::UI, FROM_HERE,
+          NewRunnableFunction(&DestroyPreloadForRenderView,
+                              final_status_it->second.prerender_manager,
+                              child_id,
+                              route_id,
+                              final_status));
+    }
+  }
+  return final_status_it->second.final_status;
+}
+
+void PrerenderTracker::AddPrerenderOnIOThread(
+    const std::pair<int, int>& child_route_id_pair) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(!IsPrerenderingOnIOThread(child_route_id_pair.first,
+                                   child_route_id_pair.second));
+
+  possibly_prerendering_io_thread_set_.insert(child_route_id_pair);
+}
+
+void PrerenderTracker::RemovePrerenderOnIOThread(
+    const std::pair<int, int>& child_route_id_pair) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(IsPrerenderingOnIOThread(child_route_id_pair.first,
+                                  child_route_id_pair.second));
+
+  possibly_prerendering_io_thread_set_.erase(child_route_id_pair);
+}
+
+// static
+void PrerenderTracker::AddPrerenderOnIOThreadTask(
+    const std::pair<int, int>& child_route_id_pair) {
+  GetInstance()->AddPrerenderOnIOThread(child_route_id_pair);
+}
+
+// static
+void PrerenderTracker::RemovePrerenderOnIOThreadTask(
+    const std::pair<int, int>& child_route_id_pair) {
+  GetInstance()->RemovePrerenderOnIOThread(child_route_id_pair);
+}
+
+}  // namespace prerender