TaskScheduler [7] SchedulerThreadPool

base/task_scheduler/scheduler_thread_pool.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_SCHEDULER_THREAD_POOL_H_
+#define BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_H_
+
+#include <stddef.h>
+
+#include <memory>
+#include <stack>
+#include <vector>
+
+#include "base/base_export.h"
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/task_runner.h"
+#include "base/task_scheduler/priority_queue.h"
+#include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/scheduler_task_executor.h"
+#include "base/task_scheduler/scheduler_worker_thread.h"
+#include "base/task_scheduler/sequence.h"
+#include "base/task_scheduler/task.h"
+#include "base/task_scheduler/task_traits.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+namespace internal {
+
+struct SequenceSortKey;
+class TaskTracker;
+
+// A pool of threads that run Tasks. This class is thread-safe.
+class BASE_EXPORT SchedulerThreadPool : public SchedulerTaskExecutor {
+ public:
+  // Callback invoked when a Sequence isn't empty after a worker thread pops a
+  // Task from it.
+  using EnqueueSequenceCallback = Callback<void(scoped_refptr<Sequence>)>;
+
+  // Destroying a SchedulerThreadPool returned by CreateThreadPool() is not
+  // allowed in production; it is always leaked. In tests, it can only be
+  // destroyed after JoinForTesting() has returned.
+  ~SchedulerThreadPool() override;
+
+  // Creates a SchedulerThreadPool with up to |max_threads| threads of priority
+  // |thread_priority|. |enqueue_sequence_callback| will be invoked after a
+  // thread of this thread pool tries to run a Task. |task_tracker| is used to
+  // handle shutdown behavior of Tasks. Returns nullptr on failure to create a
+  // thread pool with at least one thread.
+  static std::unique_ptr<SchedulerThreadPool> CreateThreadPool(
+      ThreadPriority thread_priority,
+      size_t max_threads,
+      const EnqueueSequenceCallback& enqueue_sequence_callback,
+      TaskTracker* task_tracker);
+
+  // Returns a TaskRunner whose PostTask invocations will result in scheduling
+  // Tasks with |traits| and |execution_mode| in this thread pool.
+  scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
+      const TaskTraits& traits,
+      ExecutionMode execution_mode);
+
+  // Inserts |sequence| into this thread pool's shared priority queue with
+  // |sequence_sort_key|. Must only be called from a worker thread to put
+  // |sequence| back into a PriorityQueue after running a Task from it. The
+  // worker thread doesn't have to belong to this thread pool.
+  void EnqueueSequence(scoped_refptr<Sequence> sequence,
+                       const SequenceSortKey& sequence_sort_key);
+
+  // Waits until all threads are idle.
+  void WaitForAllWorkerThreadsIdleForTesting();
+
+  // Joins all threads of this thread pool. Tasks that are already running are
+  // allowed to complete their execution. This can only be called once.
+  void JoinForTesting();
+
+  // SchedulerTaskExecutor:
+  void PostTaskWithSequence(std::unique_ptr<Task> task,
+                            scoped_refptr<Sequence> sequence) override;
+
+ private:
+  class SchedulerWorkerThreadDelegateImpl;
+
+  SchedulerThreadPool(const EnqueueSequenceCallback& enqueue_sequence_callback,
+                      TaskTracker* task_tracker);
+
+  bool Initialize(ThreadPriority thread_priority, size_t max_threads);
+
+  // Wakes up the last thread from this thread pool to go idle, if any.
+  void WakeUpOneThread();
+
+  // Adds |worker_thread| to |idle_worker_threads_stack_|.
+  void AddToIdleWorkerThreadsStack(SchedulerWorkerThread* worker_thread);
+
+  // Pops one idle worker thread from |idle_worker_thread_stack_| and returns
+  // it. Returns nullptr if |idle_worker_thread_stack_| is empty.
+  SchedulerWorkerThread* PopOneIdleWorkerThread();
+
+  // PriorityQueue from which all threads of this thread pool get work.
+  PriorityQueue shared_priority_queue_;
+
+  // All worker threads owned by this thread pool. Only modified during
+  // initialization of the thread pool.
+  std::vector<std::unique_ptr<SchedulerWorkerThread>> worker_threads_;
+
+  // Synchronizes access to |idle_worker_threads_stack_| and
+  // |idle_worker_threads_stack_cv_for_testing_|. Has |shared_priority_queue_|'s
+  // lock as its predecessor so that a thread can be pushed to
+  // |idle_worker_threads_stack_| within the scope of a Transaction (more
+  // details in GetWork()).
+  SchedulerLock idle_worker_threads_stack_lock_;
+
+  // Stack of idle worker threads.
+  std::stack<SchedulerWorkerThread*> idle_worker_threads_stack_;
+
+  // Signaled when all worker threads become idle.
+  std::unique_ptr<ConditionVariable> idle_worker_threads_stack_cv_for_testing_;
+
+  // Signaled once JoinForTesting() has returned.
+  WaitableEvent join_for_testing_returned_;
+
+  // Delegate for all worker threads in this pool.
+  std::unique_ptr<SchedulerWorkerThread::Delegate> worker_thread_delegate_;
+
+  TaskTracker* const task_tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerThreadPool);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_H_