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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/IntrusiveList.h>
#include <AK/OwnPtr.h>
#include <AK/SinglyLinkedList.h>
#include <AK/Vector.h>
namespace AK {
template<typename T, int segment_size = 1000>
class Queue {
public:
Queue() = default;
~Queue()
{
clear();
}
size_t size() const { return m_size; }
bool is_empty() const { return m_size == 0; }
template<typename U = T>
void enqueue(U&& value)
{
if (m_segments.is_empty() || m_segments.last()->data.size() >= segment_size) {
auto segment = new QueueSegment;
m_segments.append(*segment);
}
m_segments.last()->data.append(forward<U>(value));
++m_size;
}
T dequeue()
{
VERIFY(!is_empty());
auto value = move(m_segments.first()->data[m_index_into_first++]);
if (m_index_into_first == segment_size) {
delete m_segments.take_first();
m_index_into_first = 0;
}
--m_size;
if (m_size == 0 && !m_segments.is_empty()) {
// This is not necessary for correctness but avoids faulting in
// all the pages for the underlying Vector in the case where
// the caller repeatedly enqueues and then dequeues a single item.
m_index_into_first = 0;
m_segments.last()->data.clear_with_capacity();
}
return value;
}
const T& head() const
{
VERIFY(!is_empty());
return m_segments.first()->data[m_index_into_first];
}
void clear()
{
while (auto* segment = m_segments.take_first())
delete segment;
m_index_into_first = 0;
m_size = 0;
}
private:
struct QueueSegment {
Vector<T, segment_size> data;
IntrusiveListNode<QueueSegment> node;
};
IntrusiveList<QueueSegment, RawPtr<QueueSegment>, &QueueSegment::node> m_segments;
size_t m_index_into_first { 0 };
size_t m_size { 0 };
};
}
using AK::Queue;
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