Add PrerenderLocalPredictor, which will eventually perform

chrome/browser/prerender/prerender_local_predictor.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_local_predictor.h"
+
+#include "base/timer.h"
+#include "chrome/browser/prerender/prerender_manager.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/history/history.h"
+#include "chrome/browser/history/history_database.h"
+#include "content/public/browser/browser_thread.h"
+
+using content::BrowserThread;
+
+namespace prerender {
+
+namespace {
+
+// Task to lookup the URL for a given URLID.
+class GetURLForURLIDTask : public HistoryDBTask {
+ public:
+  GetURLForURLIDTask(PrerenderLocalPredictor* local_predictor,
+                     history::URLID url_id)
+      : local_predictor_(local_predictor),
+        url_id_(url_id),
+        success_(false) {
+  }
+  virtual bool RunOnDBThread(history::HistoryBackend* backend,
+                             history::HistoryDatabase* db) {
+    history::URLRow url_row;
+    success_ = db->GetURLRow(url_id_, &url_row);
+    if (success_)
+      url_ = url_row.url();
+    return true;
+  }
+  virtual void DoneRunOnMainThread() {
+    if (success_)
+      local_predictor_->OnLookupURL(url_id_, url_);
+  }
+ private:
+  PrerenderLocalPredictor* local_predictor_;
+  history::URLID url_id_;
+  bool success_;
+  GURL url_;
+  DISALLOW_COPY_AND_ASSIGN(GetURLForURLIDTask);
+};
+
+// Task to load history from the visit database on startup.
+class GetVisitHistoryTask : public HistoryDBTask {
+ public:
+  GetVisitHistoryTask(PrerenderLocalPredictor* local_predictor,
+                      int max_visits)
+      : local_predictor_(local_predictor),
+        max_visits_(max_visits),
+        visit_history_(new std::vector<history::BriefVisitInfo>) {
+  }
+  virtual bool RunOnDBThread(history::HistoryBackend* backend,
+                             history::HistoryDatabase* db) {
+    db->GetBriefVisitInfoOfMostRecentVisits(max_visits_, visit_history_.get());
+    return true;
+  }
+  virtual void DoneRunOnMainThread() {
+    local_predictor_->OnGetInitialVisitHistory(visit_history_.release());
+  }
+ private:
+  PrerenderLocalPredictor* local_predictor_;
+  int max_visits_;
+  scoped_ptr<std::vector<history::BriefVisitInfo> > visit_history_;
+  DISALLOW_COPY_AND_ASSIGN(GetVisitHistoryTask);
+};
+
+};

[brettw, 2012/04/20 22:21:50]

This line should be "}  // namespace"

[tburkard, 2012/04/20 22:56:44]

Done.

+
+HistoryService* PrerenderLocalPredictor::GetHistoryIfExists() const {
+  Profile* profile = prerender_manager_->profile();
+  if (!profile)
+    return NULL;
+  return profile->GetHistoryServiceWithoutCreating();
+}
+
+PrerenderLocalPredictor::PrerenderLocalPredictor(
+    PrerenderManager* prerender_manager)
+    : prerender_manager_(prerender_manager),
+      visit_history_initialized_(false) {
+  if (MessageLoop::current()) {
+    timer_.Start(FROM_HERE,
+                 base::TimeDelta::FromMilliseconds(kInitDelayMs),
+                 this,
+                 &PrerenderLocalPredictor::Init);
+  }
+}
+
+void PrerenderLocalPredictor::OnGetInitialVisitHistory(
+    std::vector<history::BriefVisitInfo>* visit_history) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(!visit_history_initialized_);
+  visit_history_.reset(visit_history);
+  visit_history_initialized_ = true;
+}
+
+void PrerenderLocalPredictor::Init() {
+  HistoryService* history = GetHistoryIfExists();
+  if (!history) {
+    // TODO(tburkard): Record this somewhere (eg histogram) and/or try again
+    // later.
+    return;
+  }
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  history->ScheduleDBTask(
+      new GetVisitHistoryTask(this, kMaxVisitHistory),
+      &history_db_consumer_);
+  history->AddVisitDatabaseObserver(this);
+}
+
+void PrerenderLocalPredictor::OnAddVisit(history::BriefVisitInfo info) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

[brettw, 2012/04/20 22:21:50]

You're jumping through a lot of hoops here. Say you visit a URL with 2 redirects
(not that uncommon, say an ad click). This is a lot of messages floating around.

It seems like maybe your observer should have the URL inside it. You can add the
observe at a higher level in historyBackend::AddPageVisit which has all the info
you need without doing all these extra thread hops and DB lookups.

[tburkard, 2012/04/20 22:56:44]

This is just "dummy code" at this point to demonstrate the API.  Once I commit
this change, I will immediately modify this class to actually do smart
predictions.

In that scenario, AddVisit callbacks will not trigger automatic lookups, but
only at times when we decide to do a prerender, do we need to lookup the URLID
that we would like to prerender.  So in reality, we expect this to be perhaps 1
lookup for every 5 (real, without redirects) navigations.
On 2012/04/20 22:21:50, brettw wrote:

+  HistoryService* history = GetHistoryIfExists();
+  if (history) {
+    history->ScheduleDBTask(
+        new GetURLForURLIDTask(this, info.url_id),
+        &history_db_consumer_);
+  }
+}
+
+PrerenderLocalPredictor::~PrerenderLocalPredictor() {
+  HistoryService* history = GetHistoryIfExists();
+  if (history)
+    history->RemoveVisitDatabaseObserver(this);
+}
+
+void PrerenderLocalPredictor::OnLookupURL(history::URLID url_id, GURL url) {

[brettw, 2012/04/20 22:21:50]

GURL -> const GURL&

[tburkard, 2012/04/20 22:56:44]

Done.

+
+}
+
+}  // namespace prerender