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105 lines
3.5 KiB
C++
105 lines
3.5 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_TASK_SCHEDULER_PRIORITY_QUEUE_H_
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#define BASE_TASK_TASK_SCHEDULER_PRIORITY_QUEUE_H_
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#include <memory>
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#include <queue>
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#include <vector>
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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/task_scheduler/scheduler_lock.h"
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#include "base/task/task_scheduler/sequence.h"
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#include "base/task/task_scheduler/sequence_sort_key.h"
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namespace base {
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namespace internal {
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// A PriorityQueue holds Sequences of Tasks. This class is thread-safe.
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class BASE_EXPORT PriorityQueue {
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public:
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// A Transaction can perform multiple operations atomically on a
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// PriorityQueue. While a Transaction is alive, it is guaranteed that nothing
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// else will access the PriorityQueue.
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//
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// A Worker needs to be able to Peek sequences from both its PriorityQueues
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// (single-threaded and shared) and then Pop the sequence with the highest
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// priority. If the Peek and the Pop are done through the same Transaction, it
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// is guaranteed that the PriorityQueue hasn't changed between the 2
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// operations.
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class BASE_EXPORT Transaction {
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public:
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~Transaction();
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// Inserts |sequence| in the PriorityQueue with |sequence_sort_key|.
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// Note: |sequence_sort_key| is required as a parameter instead of being
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// extracted from |sequence| in Push() to avoid this Transaction having a
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// lock interdependency with |sequence|.
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void Push(scoped_refptr<Sequence> sequence,
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const SequenceSortKey& sequence_sort_key);
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// Returns a reference to the SequenceSortKey representing the priority of
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// the highest pending task in this PriorityQueue. The reference becomes
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// invalid the next time that this PriorityQueue is modified.
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// Cannot be called on an empty PriorityQueue.
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const SequenceSortKey& PeekSortKey() const;
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// Removes and returns the highest priority Sequence in this PriorityQueue.
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// Cannot be called on an empty PriorityQueue.
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scoped_refptr<Sequence> PopSequence();
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// Returns true if the PriorityQueue is empty.
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bool IsEmpty() const;
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// Returns the number of Sequences in the PriorityQueue.
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size_t Size() const;
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private:
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friend class PriorityQueue;
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explicit Transaction(PriorityQueue* outer_queue);
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// Holds the lock of |outer_queue_| for the lifetime of this Transaction.
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AutoSchedulerLock auto_lock_;
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PriorityQueue* const outer_queue_;
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DISALLOW_COPY_AND_ASSIGN(Transaction);
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};
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PriorityQueue();
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~PriorityQueue();
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// Begins a Transaction. This method cannot be called on a thread which has an
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// active Transaction unless the last Transaction created on the thread was
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// for the allowed predecessor specified in the constructor of this
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// PriorityQueue.
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std::unique_ptr<Transaction> BeginTransaction();
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const SchedulerLock* container_lock() const { return &container_lock_; }
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private:
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// A class combining a Sequence and the SequenceSortKey that determines its
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// position in a PriorityQueue.
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class SequenceAndSortKey;
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using ContainerType = std::priority_queue<SequenceAndSortKey>;
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// Synchronizes access to |container_|.
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SchedulerLock container_lock_;
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ContainerType container_;
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DISALLOW_COPY_AND_ASSIGN(PriorityQueue);
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};
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} // namespace internal
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} // namespace base
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#endif // BASE_TASK_TASK_SCHEDULER_PRIORITY_QUEUE_H_
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