Add TaskScheduler::CreateAndSetDefaultTaskScheduler

base/task_scheduler/task_scheduler.h

 // Copyright 2016 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.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_SCHEDULER_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_H_
 
 #include <memory>
+#include <vector>
 
 #include "base/base_export.h"
 #include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "base/task_runner.h"
 #include "base/task_scheduler/task_traits.h"
 
 namespace tracked_objects {
 class Location;
 }
 
 namespace base {
 
+class SchedulerWorkerPoolParams;
+
 // Interface for a task scheduler and static methods to manage the instance used
 // by the post_task.h API.
 class BASE_EXPORT TaskScheduler {
  public:
+  // Returns the index of the worker pool in which a task with |traits| should
+  // run. This should be coded in a future-proof way: new traits should
+  // gracefully map to a default pool.
+  using WorkerPoolIndexForTraitsCallback =
+      Callback<size_t(const TaskTraits& traits)>;
+
   virtual ~TaskScheduler() = default;
 
   // Posts |task| with specific |traits|.
   // For one off tasks that don't require a TaskRunner.
   virtual void PostTaskWithTraits(const tracked_objects::Location& from_here,
                                   const TaskTraits& traits,
                                   const Closure& task) = 0;
 
   // Returns a TaskRunner whose PostTask invocations will result in scheduling
   // Tasks with |traits| which will be executed according to |execution_mode|.
   virtual scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
       const TaskTraits& traits,
       ExecutionMode execution_mode) = 0;
 
   // Synchronously shuts down the scheduler. Once this is called, only tasks
   // posted with the BLOCK_SHUTDOWN behavior will be run. When this returns:
   // - All SKIP_ON_SHUTDOWN tasks that were already running have completed their
   //   execution.
   // - All posted BLOCK_SHUTDOWN tasks have completed their execution.
   // - CONTINUE_ON_SHUTDOWN tasks might still be running.
   // Note that an implementation can keep threads and other resources alive to
   // support running CONTINUE_ON_SHUTDOWN after this returns. This can only be
   // called once.
   virtual void Shutdown() = 0;
 

[fdoray, 2016/08/02 15:01:29]

Maybe write a comment that applies to both CreateAndSetDefaultTaskScheduler and
SetInstance, and then have simpler comments that explain the particularities of
each method? Or explicitly say that this method calls SetInstance?

See
https://chromium.googlesource.com/chromium/src/+/67ecfb55741b310db7758a594ca1...

[robliao, 2016/08/02 19:29:00]

Done.

+  // Creates and sets a default task scheduler. CHECKs on failure.
+  // |worker_pool_params_vector| describes the worker pools to create.
+  // |worker_pool_index_for_traits_callback| returns the index in |worker_pools|
+  // of the worker pool in which a task with given traits should run.
+  static void CreateAndSetDefaultTaskScheduler(
+      const std::vector<SchedulerWorkerPoolParams>& worker_pool_params_vector,
+      const WorkerPoolIndexForTraitsCallback&
+          worker_pool_index_for_traits_callback);
+
   // Registers |task_scheduler| to handle tasks posted through the post_task.h
   // API for this process. The registered TaskScheduler will only be deleted
   // when a new TaskScheduler is registered (i.e. otherwise leaked on shutdown).
   // This must not be called when TaskRunners created by the previous
   // TaskScheduler are still alive. This method is not thread-safe; proper
   // synchronization is required to use the post_task.h API after registering a
   // new TaskScheduler.
   static void SetInstance(std::unique_ptr<TaskScheduler> task_scheduler);
 
   // Retrieve the TaskScheduler set via SetInstance(). This should be used very

[fdoray, 2016/08/02 15:01:29]

via SetInstance() or CreateAndSetDefaultTaskScheduler()

[robliao, 2016/08/02 19:29:00]

Done.

   // rarely; most users of TaskScheduler should use the post_task.h API.
   static TaskScheduler* GetInstance();
 };
 
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_SCHEDULER_H_