TaskScheduler [6] SchedulerWorkerThread

base/task_scheduler/worker_thread.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_WORKER_THREAD_H_
+#define BASE_TASK_SCHEDULER_WORKER_THREAD_H_
+
+#include <iosfwd>
+
+#include "base/atomicops.h"
+#include "base/base_export.h"
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/task_scheduler/priority_queue.h"
+#include "base/task_scheduler/sequence.h"
+#include "base/task_scheduler/task_traits.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+namespace internal {
+
+class TaskTracker;
+
+// A thread that runs Tasks from a shared and a single-threaded PriorityQueue.
+//
+// There is no guarantee that a WorkerThread will run work from its shared
+// PriorityQueue unless WakeUp() is called after the work is added. This allows
+// a ThreadPool to choose which WorkerThread should run the new work. On the
+// other hand, a WorkerThread is woken up automatically when Tasks are added to
+// its single-threaded PriorityQueue.
+//
+// This class is thread-safe.
+class BASE_EXPORT WorkerThread : public PlatformThread::Delegate {
+ public:
+  // Possible states for a WorkerThread.
+  enum class State {
+    BUSY,
+    IDLE,
+  };
+
+  // Callback invoked to indicate that a shared |sequence| is not empty after
+  // |worker_thread| has popped a Task from it.
+  using SharedSequenceStillHasTasksCallback =
+      Callback<void(const WorkerThread* worker_thread,
+                    scoped_refptr<Sequence> sequence)>;
+
+  // Callback invoked when the state of |worker_thread| becomes |state|. This is
+  // always invoked within the scope of an active |shared_priority_queue_|
+  // Transaction. If |state| is IDLE, it is guaranteed that
+  // |shared_priority_queue_| is empty (this can't change during the callback
+  // invocation because of the active Transaction).
+  using StateChangedCallback =
+      Callback<void(WorkerThread* worker_thread, State state)>;
+
+  // Creates a WorkerThread with priority |thread_priority| that runs Tasks from
+  // its single-threaded PriorityQueue and from |shared_priority_queue|.
+  // |shared_sequence_still_has_tasks_callback| is invoked when a Sequence
+  // extracted from |shared_priority_queue| isn't empty after the WorkerThread
+  // has popped a task from it. |state_changed_callback| is invoked when the
+  // WorkerThread becomes IDLE or BUSY. |task_tracker| is used to handle
+  // shutdown behavior of Tasks.
+  static scoped_ptr<WorkerThread> CreateWorkerThread(
+      ThreadPriority thread_priority,
+      PriorityQueue* shared_priority_queue,
+      const SharedSequenceStillHasTasksCallback&
+          shared_sequence_still_has_tasks_callback,
+      const StateChangedCallback& state_changed_callback,
+      TaskTracker* task_tracker);
+
+  // Destroying a WorkerThread in production is not allowed; it is always
+  // leaked. In tests, it can only be destroyed after JoinForTesting() has
+  // returned.
+  ~WorkerThread() override;
+
+  // Wakes up this WorkerThread. When this is called, this WorkerThread will run
+  // until both its PriorityQueues become empty.
+  void WakeUp();
+
+  // Returns a SingleThreadTaskRunner whose PostTask invocations will result in
+  // scheduling Tasks with |traits| on this WorkerThread.
+  scoped_refptr<SingleThreadTaskRunner> CreateTaskRunnerWithTraits(
+      const TaskTraits& traits);
+
+  // Joins this WorkerThread. If a Task is already running, it will be allowed
+  // to complete its execution. This can only be called once.
+  void JoinForTesting();
+
+ private:
+  WorkerThread(ThreadPriority thread_priority,
+               PriorityQueue* shared_priority_queue,
+               const SharedSequenceStillHasTasksCallback&
+                   shared_sequence_still_has_tasks_callback,
+               const StateChangedCallback& state_changed_callback,
+               TaskTracker* task_tracker);
+
+  // Sets the state of this WorkerThread.
+  void SetState(State state);
+
+  // PlatformThread::Delegate:
+  void ThreadMain() override;
+
+  bool should_exit_for_testing() const {
+    base::subtle::MemoryBarrier();
+    return should_exit_for_testing_;
+  }
+
+  // Platform thread managed by this WorkerThread.
+  PlatformThreadHandle thread_handle_;
+
+  // Current state of this WorkerThread.
+  State state_ = State::BUSY;
+
+  // Event signaled to wake up this WorkerThread.
+  WaitableEvent wake_up_event_;
+
+  // The single-threaded PriorityQueue from which this WorkerThread gets work.
+  PriorityQueue single_thread_priority_queue_;
+
+  // The shared PriorityQueue from which this WorkerThread gets work.
+  PriorityQueue* const shared_priority_queue_;
+
+  const SharedSequenceStillHasTasksCallback
+      shared_sequence_still_has_tasks_callback_;
+  const StateChangedCallback state_changed_callback_;
+  TaskTracker* const task_tracker_;
+
+  // True once JoinForTesting() has been called.
+  bool should_exit_for_testing_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(WorkerThread);
+};
+
+BASE_EXPORT std::ostream& operator<<(std::ostream& os,
+                                     WorkerThread::State state);
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_WORKER_THREAD_H_