Reference CL for the new task scheduler.

base/task_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_THREAD_POOL_H_
+#define BASE_TASK_SCHEDULER_THREAD_POOL_H_
+
+#include <set>
+#include <stack>
+#include <vector>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/task_scheduler/delayed_task_manager.h"
+#include "base/task_scheduler/priority_queue.h"
+#include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/sequence.h"
+#include "base/task_scheduler/worker_thread.h"
+#include "base/threading/platform_thread.h"
+#include "base/threading/thread_local.h"
+
+namespace base {
+struct TaskTraits;
+}  // namespace base
+
+namespace base {
+namespace internal {
+
+class SequenceSortKey;
+class ShutdownManager;
+
+// A pool of threads that run tasks. This class is thread-safe.
+class BASE_EXPORT ThreadPool {
+ public:
+  ~ThreadPool();
+
+  // Creates a pool with |num_threads| threads of priority |thread_priority|.
+  // |reinsert_sequence_callback| is invoked to reinsert a sequence in the
+  // appropriate priority queue after one of its tasks has been executed.
+  // |shutdown_manager| is used to handle shutdown behavior of tasks. Returns
+  // nullptr if it wasn't possible to create at least 1 thread.
+  static scoped_ptr<ThreadPool> CreateThreadPool(
+      ThreadPriority thread_priority,
+      size_t num_threads,
+      const WorkerThread::ReinsertSequenceCallback& reinsert_sequence_callback,
+      ShutdownManager* shutdown_manager);
+
+  // Returns the number of threads in the pool. This can be less than the number
+  // of threads requested when the pool was created.
+  size_t GetNumThreads() const;
+
+  // Returns a TaskRunner whose PostTask invocations will result in scheduling
+  // tasks within this thread pool with traits |traits| and execution mode
+  // |execution_mode|.
+  scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
+      const TaskTraits& traits,
+      ExecutionMode execution_mode);
+
+  // Reinserts |sequence| in the priority queue of this thread pool with sort
+  // key |sequence_sort_key| after one of its tasks has been executed. Note that
+  // the task could have been executed by a worker thread from this pool or from
+  // another pool.
+  void ReinsertSequence(scoped_refptr<Sequence> sequence,
+                        const SequenceSortKey& sequence_sort_key,
+                        const WorkerThread* worker_thread);
+
+  // Initiates shutdown and waits until all threads have exited. This method
+  // must not be called more than once in the lifetime of the ThreadPool.
+  void ShutdownAndJoinAllThreadsForTesting();
+
+ private:
+  ThreadPool(
+      ThreadPriority thread_priority,
+      size_t num_threads,
+      const WorkerThread::ReinsertSequenceCallback& reinsert_sequence_callback,
+      ShutdownManager* shutdown_manager);
+
+  // Invoked by |worker_thread| when it becomes idle. |worker_thread| has to
+  // belong to this thread pool.
+  void WorkerThreadBecomesIdleCallback(WorkerThread* worker_thread);
+
+  // Wakes up 1 thread from the pool if not all threads are busy.
+  void WakeUpOneThread();
+
+  // Callback invoked when a sequence is inserted in |priority_queue_|.
+  void OnSequenceInsertedInPriorityQueue();
+
+  // Signaled when the threadpool data structures are ready.
+  WaitableEvent thread_pool_ready_;
+
+  // Priority queue from which all worker threads of this pool get work.
+  PriorityQueue priority_queue_;
+
+  // All the worker threads owned by this thread pool.
+  std::vector<scoped_ptr<WorkerThread>> worker_threads_;
+
+  // Lock protecting |idle_worker_threads_stack_| and |idle_threads_set_|.
+  SchedulerLock idle_worker_threads_lock_;
+
+  // Stack of possibly idle worker threads. The last worker thread that became
+  // idle is on top of the stack. When a thread is woken up to execute single-
+  // threaded tasks, it is not removed from this stack. That means that a thread
+  // can be on this stack without actually being idle.
+  std::stack<WorkerThread*> idle_worker_threads_stack_;
+
+  // Set of worker threads that are in |idle_worker_threads_stack_|.
+  std::set<WorkerThread*> idle_worker_threads_set_;
+
+  // Indicates that no worker thread should be woken up when a sequence is
+  // inserted in |priority_queue_| by a given thread.
+  ThreadLocalBoolean disable_wake_up_thread_on_sequence_insertion_;
+
+  ShutdownManager* const shutdown_manager_;
+
+  // Manages delayed tasks posted to this thread pool.
+  DelayedTaskManager delayed_task_manager_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadPool);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_THREAD_POOL_H_