Move Task Scheduler Initialization From chrome/browser to Content

chrome/browser/chrome_browser_main.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/chrome_browser_main.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <set>
@@ skipping 15 matching lines @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/run_loop.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
-#include "base/task_scheduler/task_scheduler.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "cc/base/switches.h"
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/after_startup_task_utils.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 81 matching lines @@
 #include "components/metrics_services_manager/metrics_services_manager.h"
 #include "components/nacl/browser/nacl_browser.h"
 #include "components/prefs/json_pref_store.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
 #include "components/prefs/pref_value_store.h"
 #include "components/prefs/scoped_user_pref_update.h"
 #include "components/rappor/rappor_service.h"
 #include "components/signin/core/common/profile_management_switches.h"
 #include "components/startup_metric_utils/browser/startup_metric_utils.h"
-#include "components/task_scheduler_util/initialization_util.h"
 #include "components/tracing/common/tracing_switches.h"
 #include "components/translate/core/browser/translate_download_manager.h"
 #include "components/variations/field_trial_config/field_trial_util.h"
 #include "components/variations/pref_names.h"
 #include "components/variations/service/variations_service.h"
 #include "components/variations/variations_associated_data.h"
 #include "components/variations/variations_http_header_provider.h"
 #include "components/variations/variations_switches.h"
 #include "components/version_info/version_info.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 1043 matching lines @@
   // Must be done after g_browser_process is constructed, before
   // SetupFieldTrials() and SetupMetrics().
   chromeos::CrosSettings::Initialize();
 #endif  // defined(OS_CHROMEOS)
 
   SetupOriginTrialsCommandLine();
 
   device::GeolocationProvider::SetGeolocationDelegate(
       new ChromeGeolocationDelegate());
 
   // IMPORTANT

[gab, 2016/11/30 22:36:58]

Does this comment apply anymore? i.e. it's relevant to this whole method but the
things at the end here are no longer special?

[robliao, 2016/12/06 01:31:30]

Moved to top and reworded.

   // Do not add anything below this line until you've verified your new code
-  // does not interfere with the critical initialization order below. Some of
-  // the calls below end up implicitly creating threads and as such new calls
-  // typically either belong before them or in a later startup phase.
+  // does not interfere with the critical initialization order below. Calls
+  // after this line should not post tasks or create threads. This work should
+  // be deferred to PreMainMessageLoopRunImpl.
 
   // Now that the command line has been mutated based on about:flags, we can
   // initialize field trials and setup metrics. The field trials are needed by

[gab, 2016/11/30 22:36:58]

No longer sets up metrics

[robliao, 2016/12/06 01:31:30]

Reworded. The only implication here is that we can now setup metrics but we wait
for PreMainMessageLoopRunImpl.

   // IOThread's initialization which happens in BrowserProcess:PreCreateThreads.
   SetupFieldTrials();
 
-  // Task Scheduler initialization needs to be here for the following reasons:
-  //   * After |SetupFieldTrials()|: Initialization uses variations.
-  //   * Near the end of |PreCreateThreads()|: The TaskScheduler needs to be
-  //         created before any other threads are (by contract) but it creates
-  //         threads itself so instantiating it earlier is also incorrect.
-  // To maintain scoping symmetry, if this line is moved, the corresponding
-  // shutdown call may also need to be moved.
-  task_scheduler_util::InitializeDefaultBrowserTaskScheduler();
-
   // ChromeOS needs ResourceBundle::InitSharedInstance to be called before this.
   // This also instantiates the IOThread which requests the metrics service and
   // must be after |SetupMetrics()|.
   browser_process_->PreCreateThreads();
 
   return content::RESULT_CODE_NORMAL_EXIT;
 }
 
 void ChromeBrowserMainParts::ServiceManagerConnectionStarted(
     content::ServiceManagerConnection* connection) {
@@ skipping 831 matching lines @@
                          ? browser_shutdown::RESTART_IN_BACKGROUND
                          : browser_shutdown::NO_FLAGS;
   }
 #endif  // BUILDFLAG(ENABLE_BACKGROUND)
 
   browser_process_->PostDestroyThreads();
   // browser_shutdown takes care of deleting browser_process, so we need to
   // release it.
   ignore_result(browser_process_.release());
 
-  // The TaskScheduler was initialized before invoking
-  // |browser_process_->PreCreateThreads()|. To maintain scoping symmetry,
-  // perform the shutdown after |browser_process_->PostDestroyThreads()|.
-  base::TaskScheduler* task_scheduler = base::TaskScheduler::GetInstance();
-  if (task_scheduler)
-    task_scheduler->Shutdown();
-
   browser_shutdown::ShutdownPostThreadsStop(restart_flags);
   master_prefs_.reset();
   process_singleton_.reset();
   device_event_log::Shutdown();
 
   // We need to do this check as late as possible, but due to modularity, this
   // may be the last point in Chrome.  This would be more effective if done at
   // a higher level on the stack, so that it is impossible for an early return
   // to bypass this code.  Perhaps we need a *final* hook that is called on all
   // paths from content/browser/browser_main.
   CHECK(metrics::MetricsService::UmaMetricsProperlyShutdown());
 
 #if defined(OS_CHROMEOS)
   chromeos::CrosSettings::Shutdown();
 #endif  // defined(OS_CHROMEOS)
 #endif  // defined(OS_ANDROID)
 }
 
 // Public members:
 
 void ChromeBrowserMainParts::AddParts(ChromeBrowserMainExtraParts* parts) {
   chrome_extra_parts_.push_back(parts);
 }