TaskScheduler: Make the worker pools of TaskSchedulerImpl configurable

base/task_scheduler/task_scheduler_impl.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_IMPL_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 
+#include <stddef.h>
+
 #include <memory>
+#include <string>
+#include <vector>
 
 #include "base/base_export.h"
+#include "base/callback.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/task_runner.h"
 #include "base/task_scheduler/delayed_task_manager.h"
+#include "base/task_scheduler/scheduler_worker_pool_impl.h"
 #include "base/task_scheduler/sequence.h"
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/task_scheduler/task_tracker.h"
 #include "base/task_scheduler/task_traits.h"
+#include "base/threading/thread.h"
 
 namespace base {
 namespace internal {
 
 class SchedulerServiceThread;
-class SchedulerWorkerPoolImpl;
 
 // Default TaskScheduler implementation. This class is thread-safe.
 class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
  public:
+  struct WorkerPoolCreationArgs {
+    // Name of the pool. Used to label the pool's threads.
+    std::string name;
+
+    // Priority of the pool's threads.
+    ThreadPriority thread_priority;
+
+    // Whether I/O is allowed in the pool.
+    SchedulerWorkerPoolImpl::IORestriction io_restriction;
+
+    // Maximum number of threads in the pool.
+    size_t max_threads;
+  };
+
+  // Returns the index of the worker pool in which a task with |traits| should
+  // run.

[robliao, 2016/06/23 22:37:03]

Also document that this should be coded in a future-proof way. New traits should
gracefully map to a default pool.

[fdoray, 2016/06/27 19:45:04]

Done.

+  using WorkerPoolIndexForTraitsCallback =
+      Callback<size_t(const TaskTraits& traits)>;
+
   // Creates and returns an initialized TaskSchedulerImpl. CHECKs on failure to
-  // do so (never returns null).
-  static std::unique_ptr<TaskSchedulerImpl> Create();
+  // do so (never returns null). |worker_pools| is a list of worker pools to

[robliao, 2016/06/23 22:37:03]

Nit: "CHECKs on failure" is sufficient.

[fdoray, 2016/06/27 19:45:04]

Done.

+  // create. |worker_pool_index_for_traits_callback| returns the index in

[robliao, 2016/06/23 22:37:03]

|worker_pools| describes the worker pools to create.

[fdoray, 2016/06/27 19:45:04]

Done.

+  // |worker_pools| of the worker pool in which a task with given traits should
+  // run.
+  static std::unique_ptr<TaskSchedulerImpl> Create(
+      const std::vector<WorkerPoolCreationArgs>& worker_pools,
+      const WorkerPoolIndexForTraitsCallback&
+          worker_pool_index_for_traits_callback);
 
   // Destroying a TaskSchedulerImpl is not allowed in production; it is always
   // leaked. In tests, it can only be destroyed after JoinForTesting() has
   // returned.
   ~TaskSchedulerImpl() override;
 
   // TaskScheduler:
   void PostTaskWithTraits(const tracked_objects::Location& from_here,
                           const TaskTraits& traits,
                           const Closure& task) override;
   scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
       const TaskTraits& traits,
       ExecutionMode execution_mode) override;
   void Shutdown() override;
 
   // Joins all threads of this scheduler. Tasks that are already running are
   // allowed to complete their execution. This can only be called once.
   void JoinForTesting();
 
  private:
-  TaskSchedulerImpl();
+  TaskSchedulerImpl(const WorkerPoolIndexForTraitsCallback&
+                        worker_pool_index_for_traits_callback);
 
-  void Initialize();
+  void Initialize(const std::vector<WorkerPoolCreationArgs>& worker_pools);
 
   // Returns the worker pool that runs Tasks with |traits|.
   SchedulerWorkerPool* GetWorkerPoolForTraits(const TaskTraits& traits);
 
   // Callback invoked when a non-single-thread |sequence| isn't empty after a
   // worker pops a Task from it.
   void ReEnqueueSequenceCallback(scoped_refptr<Sequence> sequence);
 
   // Callback invoked when the delayed run time is changed from the
   // DelayedTaskManager.
   void OnDelayedRunTimeUpdated();
 
   TaskTracker task_tracker_;
   DelayedTaskManager delayed_task_manager_;
-
-  // Worker pool for BACKGROUND Tasks without file I/O.
-  std::unique_ptr<SchedulerWorkerPoolImpl> background_worker_pool_;
-
-  // Worker pool for BACKGROUND Tasks with file I/O.
-  std::unique_ptr<SchedulerWorkerPoolImpl> background_file_io_worker_pool_;
-
-  // Worker pool for USER_VISIBLE and USER_BLOCKING Tasks without file I/O.
-  std::unique_ptr<SchedulerWorkerPoolImpl> normal_worker_pool_;
-
-  // Worker pool for USER_VISIBLE and USER_BLOCKING Tasks with file I/O.
-  std::unique_ptr<SchedulerWorkerPoolImpl> normal_file_io_worker_pool_;
-
+  const WorkerPoolIndexForTraitsCallback worker_pool_index_for_traits_callback_;
+  std::vector<std::unique_ptr<SchedulerWorkerPoolImpl>> worker_pools_;
   std::unique_ptr<SchedulerServiceThread> service_thread_;
 
 #if DCHECK_IS_ON()
   // Signaled once JoinForTesting() has returned.
   WaitableEvent join_for_testing_returned_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(TaskSchedulerImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_