| // 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_SEQUENCE_H_ |
| #define BASE_TASK_SCHEDULER_SEQUENCE_H_ |
| |
| #include <stddef.h> |
| |
| #include <memory> |
| #include <queue> |
| |
| #include "base/base_export.h" |
| #include "base/macros.h" |
| #include "base/memory/ref_counted.h" |
| #include "base/task_scheduler/scheduler_lock.h" |
| #include "base/task_scheduler/sequence_sort_key.h" |
| #include "base/task_scheduler/task.h" |
| #include "base/task_scheduler/task_traits.h" |
| |
| namespace base { |
| namespace internal { |
| |
| // A sequence holds tasks that must be executed in posting order. |
| // |
| // Note: there is a known refcounted-ownership cycle in the Scheduler |
| // architecture: Sequence -> Task -> TaskRunner -> Sequence -> ... |
| // This is okay so long as the other owners of Sequence (PriorityQueue and |
| // SchedulerWorkerThread in alternance and |
| // SchedulerThreadPoolImpl::SchedulerWorkerThreadDelegateImpl::GetWork() |
| // temporarily) keep running it (and taking Tasks from it as a result). A |
| // dangling reference cycle would only occur should they release their reference |
| // to it while it's not empty. In other words, it is only correct for them to |
| // release it after PopTask() returns false to indicate it was made empty by |
| // that call (in which case the next PushTask() will return true to indicate to |
| // the caller that the Sequence should be re-enqueued for execution). |
| // |
| // This class is thread-safe. |
| class BASE_EXPORT Sequence : public RefCountedThreadSafe<Sequence> { |
| public: |
| Sequence(); |
| |
| // Adds |task| at the end of the sequence's queue. Returns true if the |
| // sequence was empty before this operation. |
| bool PushTask(std::unique_ptr<Task> task); |
| |
| // Returns the task in front of the sequence's queue, if any. |
| const Task* PeekTask() const; |
| |
| // Removes the task in front of the sequence's queue. Returns true if the |
| // sequence is empty after this operation. Cannot be called on an empty |
| // sequence. |
| bool PopTask(); |
| |
| // Returns a SequenceSortKey representing the priority of the sequence. Cannot |
| // be called on an empty sequence. |
| SequenceSortKey GetSortKey() const; |
| |
| private: |
| friend class RefCountedThreadSafe<Sequence>; |
| ~Sequence(); |
| |
| // Synchronizes access to all members. |
| mutable SchedulerLock lock_; |
| |
| // Queue of tasks to execute. |
| std::queue<std::unique_ptr<Task>> queue_; |
| |
| // Number of tasks contained in the sequence for each priority. |
| size_t num_tasks_per_priority_[static_cast<int>(TaskPriority::HIGHEST) + 1] = |
| {}; |
| |
| DISALLOW_COPY_AND_ASSIGN(Sequence); |
| }; |
| |
| } // namespace internal |
| } // namespace base |
| |
| #endif // BASE_TASK_SCHEDULER_SEQUENCE_H_ |