79 lines
2.6 KiB
C++
79 lines
2.6 KiB
C++
// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_TASK_SCHEDULER_SEQUENCE_H_
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#define BASE_TASK_SCHEDULER_SEQUENCE_H_
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#include <stddef.h>
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#include <memory>
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#include <queue>
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#include "base/base_export.h"
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#include "base/macros.h"
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#include "base/memory/ref_counted.h"
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#include "base/task_scheduler/scheduler_lock.h"
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#include "base/task_scheduler/sequence_sort_key.h"
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#include "base/task_scheduler/task.h"
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#include "base/task_scheduler/task_traits.h"
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namespace base {
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namespace internal {
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// A sequence holds tasks that must be executed in posting order.
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//
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// Note: there is a known refcounted-ownership cycle in the Scheduler
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// architecture: Sequence -> Task -> TaskRunner -> Sequence -> ...
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// This is okay so long as the other owners of Sequence (PriorityQueue and
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// SchedulerWorker in alternation and
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// SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::GetWork()
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// temporarily) keep running it (and taking Tasks from it as a result). A
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// dangling reference cycle would only occur should they release their reference
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// to it while it's not empty. In other words, it is only correct for them to
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// release it after PopTask() returns false to indicate it was made empty by
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// that call (in which case the next PushTask() will return true to indicate to
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// the caller that the Sequence should be re-enqueued for execution).
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//
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// This class is thread-safe.
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class BASE_EXPORT Sequence : public RefCountedThreadSafe<Sequence> {
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public:
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Sequence();
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// Adds |task| at the end of the sequence's queue. Returns true if the
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// sequence was empty before this operation.
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bool PushTask(std::unique_ptr<Task> task);
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// Returns the task in front of the sequence's queue, if any.
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const Task* PeekTask() const;
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// Removes the task in front of the sequence's queue. Returns true if the
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// sequence is empty after this operation. Cannot be called on an empty
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// sequence.
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bool PopTask();
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// Returns a SequenceSortKey representing the priority of the sequence. Cannot
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// be called on an empty sequence.
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SequenceSortKey GetSortKey() const;
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private:
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friend class RefCountedThreadSafe<Sequence>;
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~Sequence();
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// Synchronizes access to all members.
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mutable SchedulerLock lock_;
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// Queue of tasks to execute.
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std::queue<std::unique_ptr<Task>> queue_;
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// Number of tasks contained in the sequence for each priority.
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size_t num_tasks_per_priority_[static_cast<int>(TaskPriority::HIGHEST) + 1] =
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{};
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DISALLOW_COPY_AND_ASSIGN(Sequence);
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};
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} // namespace internal
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} // namespace base
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#endif // BASE_TASK_SCHEDULER_SEQUENCE_H_
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