Move the pref service from the IO thread to a task scheduler sequence.

Bug: 654988
Change-Id: I7f91eafc52aed40c8243e657b85c821605f9c76b
Reviewed-on: https://chromium-review.googlesource.com/526914Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481028}

chrome/browser/browser_process_impl.cc

@@ -469,18 +469,14 @@ void BrowserProcessImpl::EndSession() {
   ProfileManager* pm = profile_manager();
   std::vector<Profile*> profiles(pm->GetLoadedProfiles());
   scoped_refptr<RundownTaskCounter> rundown_counter(new RundownTaskCounter());
-  const bool pref_service_enabled =
-      base::FeatureList::IsEnabled(features::kPrefService);
   std::vector<scoped_refptr<base::SequencedTaskRunner>> profile_writer_runners;
   for (size_t i = 0; i < profiles.size(); ++i) {
     Profile* profile = profiles[i];
     profile->SetExitType(Profile::EXIT_SESSION_ENDED);
     if (profile->GetPrefs()) {
       profile->GetPrefs()->CommitPendingWrite();
-      if (pref_service_enabled) {
-        rundown_counter->Post(content::BrowserThread::GetTaskRunnerForThread(
-                                  content::BrowserThread::IO)
-                                  .get());
+      if (profile->GetPrefServiceTaskRunner()) {
+        rundown_counter->Post(profile->GetPrefServiceTaskRunner().get());
         profile_writer_runners.push_back(profile->GetIOTaskRunner());
       } else {
         rundown_counter->Post(profile->GetIOTaskRunner().get());
@@ -527,7 +523,7 @@ void BrowserProcessImpl::EndSession() {
   // http://crbug.com/318527.
   const base::TimeTicks end_time = base::TimeTicks::Now() + kEndSessionTimeout;
   const bool timed_out = !rundown_counter->TimedWaitUntil(end_time);
-  if (timed_out || !pref_service_enabled)
+  if (timed_out || !base::FeatureList::IsEnabled(features::kPrefService))
     return;
 
   scoped_refptr<RundownTaskCounter> profile_write_rundown_counter(

chrome/browser/profiles/off_the_record_profile_impl.cc

@@ -387,8 +387,10 @@ void OffTheRecordProfileImpl::RegisterInProcessServices(
     info.factory = base::Bind(
         &prefs::CreatePrefService, chrome::ExpectedPrefStores(),
         make_scoped_refptr(content::BrowserThread::GetBlockingPool()));
-    info.task_runner = content::BrowserThread::GetTaskRunnerForThread(
-        content::BrowserThread::IO);
+    info.task_runner = base::CreateSequencedTaskRunnerWithTraits(
+        {base::TaskShutdownBehavior::BLOCK_SHUTDOWN,
+         base::TaskPriority::USER_VISIBLE});
+    pref_service_task_runner_ = info.task_runner;
     services->insert(std::make_pair(prefs::mojom::kServiceName, info));
   }
 }
@@ -499,6 +501,11 @@ Profile::ExitType OffTheRecordProfileImpl::GetLastSessionExitType() {
   return profile_->GetLastSessionExitType();
 }
 
+scoped_refptr<base::SequencedTaskRunner>
+OffTheRecordProfileImpl::GetPrefServiceTaskRunner() {
+  return pref_service_task_runner_;
+}
+
 #if defined(OS_CHROMEOS)
 void OffTheRecordProfileImpl::ChangeAppLocale(const std::string& locale,
                                               AppLocaleChangedVia) {

chrome/browser/profiles/off_the_record_profile_impl.h

@@ -80,6 +80,7 @@ class OffTheRecordProfileImpl : public Profile {
   bool WasCreatedByVersionOrLater(const std::string& version) override;
   void SetExitType(ExitType exit_type) override;
   ExitType GetLastSessionExitType() override;
+  scoped_refptr<base::SequencedTaskRunner> GetPrefServiceTaskRunner() override;
 
 #if defined(OS_CHROMEOS)
   void ChangeAppLocale(const std::string& locale, AppLocaleChangedVia) override;
@@ -139,6 +140,7 @@ class OffTheRecordProfileImpl : public Profile {
   Profile* profile_;
 
   std::unique_ptr<sync_preferences::PrefServiceSyncable> prefs_;
+  scoped_refptr<base::SequencedTaskRunner> pref_service_task_runner_;
 
 #if !defined(OS_ANDROID)
   std::unique_ptr<content::HostZoomMap::Subscription> track_zoom_subscription_;

chrome/browser/profiles/profile.h

@@ -303,6 +303,10 @@ class Profile : public content::BrowserContext {
   // Returns how the last session was shutdown.
   virtual ExitType GetLastSessionExitType() = 0;
 
+  // Returns the SequencedTaskRunner the pref service runs on.
+  virtual scoped_refptr<base::SequencedTaskRunner>
+  GetPrefServiceTaskRunner() = 0;
+
   // Stop sending accessibility events until ResumeAccessibilityEvents().
   // Calls to Pause nest; no events will be sent until the number of
   // Resume calls matches the number of Pause calls received.

chrome/browser/profiles/profile_browsertest.cc

@@ -715,9 +715,7 @@ IN_PROC_BROWSER_TEST_F(ProfileBrowserTest,
     profile->SetExitType(Profile::EXIT_CRASHED);
     profile->GetPrefs()->CommitPendingWrite();
     if (base::FeatureList::IsEnabled(features::kPrefService)) {
-      FlushTaskRunner(content::BrowserThread::GetTaskRunnerForThread(
-                          content::BrowserThread::IO)
-                          .get());
+      FlushTaskRunner(profile->GetPrefServiceTaskRunner().get());
     }
     FlushTaskRunner(profile->GetIOTaskRunner().get());
 

chrome/browser/profiles/profile_impl.cc

@@ -979,6 +979,11 @@ Profile::ExitType ProfileImpl::GetLastSessionExitType() {
   return last_session_exit_type_;
 }
 
+scoped_refptr<base::SequencedTaskRunner>
+ProfileImpl::GetPrefServiceTaskRunner() {
+  return pref_service_task_runner_;
+}
+
 PrefService* ProfileImpl::GetPrefs() {
   return const_cast<PrefService*>(
       static_cast<const ProfileImpl*>(this)->GetPrefs());
@@ -1126,8 +1131,10 @@ void ProfileImpl::RegisterInProcessServices(StaticServiceMap* services) {
     info.factory = base::Bind(
         &prefs::CreatePrefService, chrome::ExpectedPrefStores(),
         make_scoped_refptr(content::BrowserThread::GetBlockingPool()));
-    info.task_runner = content::BrowserThread::GetTaskRunnerForThread(
-        content::BrowserThread::IO);
+    info.task_runner = base::CreateSequencedTaskRunnerWithTraits(
+        {base::TaskShutdownBehavior::BLOCK_SHUTDOWN,
+         base::TaskPriority::USER_VISIBLE});
+    pref_service_task_runner_ = info.task_runner;
     services->insert(std::make_pair(prefs::mojom::kServiceName, info));
   }
 

chrome/browser/profiles/profile_impl.h

@@ -145,6 +145,7 @@ class ProfileImpl : public Profile {
   bool WasCreatedByVersionOrLater(const std::string& version) override;
   void SetExitType(ExitType exit_type) override;
   ExitType GetLastSessionExitType() override;
+  scoped_refptr<base::SequencedTaskRunner> GetPrefServiceTaskRunner() override;
 
 #if defined(OS_CHROMEOS)
   void ChangeAppLocale(const std::string& locale, AppLocaleChangedVia) override;
@@ -233,6 +234,7 @@ class ProfileImpl : public Profile {
   // first.
   scoped_refptr<user_prefs::PrefRegistrySyncable> pref_registry_;
   std::unique_ptr<sync_preferences::PrefServiceSyncable> prefs_;
+  scoped_refptr<base::SequencedTaskRunner> pref_service_task_runner_;
   // See comment in GetOffTheRecordPrefs. Field exists so something owns the
   // dummy.
   std::unique_ptr<sync_preferences::PrefServiceSyncable> dummy_otr_prefs_;

chrome/browser/ui/app_list/test/fake_profile.cc

@@ -210,3 +210,9 @@ void FakeProfile::SetExitType(ExitType exit_type) {
 Profile::ExitType FakeProfile::GetLastSessionExitType() {
   return EXIT_NORMAL;
 }
+
+scoped_refptr<base::SequencedTaskRunner>
+FakeProfile::GetPrefServiceTaskRunner() {
+  NOTIMPLEMENTED();
+  return nullptr;
+}

chrome/browser/ui/app_list/test/fake_profile.h

@@ -94,6 +94,7 @@ class FakeProfile : public Profile {
   bool WasCreatedByVersionOrLater(const std::string& version) override;
   void SetExitType(ExitType exit_type) override;
   ExitType GetLastSessionExitType() override;
+  scoped_refptr<base::SequencedTaskRunner> GetPrefServiceTaskRunner() override;
 
  private:
   std::string name_;

chrome/test/base/testing_profile.cc

@@ -1050,6 +1050,12 @@ Profile::ExitType TestingProfile::GetLastSessionExitType() {
   return last_session_exited_cleanly_ ? EXIT_NORMAL : EXIT_CRASHED;
 }
 
+scoped_refptr<base::SequencedTaskRunner>
+TestingProfile::GetPrefServiceTaskRunner() {
+  NOTIMPLEMENTED();
+  return nullptr;
+}
+
 TestingProfile::Builder::Builder()
     : build_called_(false),
       delegate_(NULL),

chrome/test/base/testing_profile.h

@@ -327,6 +327,7 @@ class TestingProfile : public Profile {
   bool IsGuestSession() const override;
   void SetExitType(ExitType exit_type) override {}
   ExitType GetLastSessionExitType() override;
+  scoped_refptr<base::SequencedTaskRunner> GetPrefServiceTaskRunner() override;
 #if defined(OS_CHROMEOS)
   void ChangeAppLocale(const std::string&, AppLocaleChangedVia) override {}
   void OnLogin() override {}