chromium/base/task/sequence_manager/lazily_deallocated_deque.h

// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_TASK_SEQUENCE_MANAGER_LAZILY_DEALLOCATED_DEQUE_H_
#define BASE_TASK_SEQUENCE_MANAGER_LAZILY_DEALLOCATED_DEQUE_H_

#include <algorithm>
#include <cmath>
#include <limits>
#include <memory>
#include <utility>
#include <vector>

#include "base/check.h"
#include "base/check_op.h"
#include "base/containers/span.h"
#include "base/debug/alias.h"
#include "base/gtest_prod_util.h"
#include "base/memory/raw_ptr.h"
#include "base/memory/raw_ptr_exclusion.h"
#include "base/memory/raw_span.h"
#include "base/time/time.h"

namespace base {
namespace sequence_manager {
namespace internal {

// A LazilyDeallocatedDeque specialized for the SequenceManager's usage
// patterns. The queue generally grows while tasks are added and then removed
// until empty and the cycle repeats.
//
// The main difference between sequence_manager::LazilyDeallocatedDeque and
// others is memory management.  For performance (memory allocation isn't free)
// we don't automatically reclaiming memory when the queue becomes empty.
// Instead we rely on the surrounding code periodically calling
// MaybeShrinkQueue, ideally when the queue is empty.
//
// We keep track of the maximum recent queue size and rate limit
// MaybeShrinkQueue to avoid unnecessary churn.
//
// NB this queue isn't by itself thread safe.
template <typename T, TimeTicks (*now_source)() = TimeTicks::Now>
class LazilyDeallocatedDeque { … };

}  // namespace internal
}  // namespace sequence_manager
}  // namespace base

#endif  // BASE_TASK_SEQUENCE_MANAGER_LAZILY_DEALLOCATED_DEQUE_H_